Fabrication of Aluminum Alloys

## **Chapter 3**

## Quality Assurance of Aluminium Extrusion for 6xxx Series Alloys

*Ying Pio Lim and Heng Kam Lim*

## **Abstract**

Aluminium extrusion of 6xxx series alloys is gaining more and more importance and indispensable in the market for applications in automotive (great potential for EV in the near future by 2030), construction, architecture, electronics, marine and rail transport. The 6000 series alloys can be divided into soft alloy (e.g. 6060, 6063) and hard alloy (e.g. 6005A, 6061, 6082) for different applications based on customer's requirements for tensile strength, yield strength, elongation, surface finishing (powder coating and anodizing) and heat treatment. To produce good quality extrudates with quality that can meet customer's stringent requirements has become a challenging job nowadays for extruders in developing country like Malaysia. In order to be competitive in the global market, the products have to be produced at minimum cost and just-in-time to meet the committed delivery date. This will require a very good implementation of quality system in the production to ensure customer's satisfaction is achieved from time to time. Based on the real experiences of working in an international scale extruder, the effective methods taken to improve product quality and productivity are elaborated throughout the chapter.

**Keywords:** aluminium alloy, extrusion, defects, quality assurance, material handling

## **1. Introduction**

Aluminium alloy can be defined as a substance having metallic properties and composed of two or more alloying elements of which the base metal is aluminium. Most aluminium alloys contain 90–96% aluminium, with one or more other elements added to provide a specific combination of properties and characteristics. It is quite usual to have several minor alloying elements in addition to one or two major alloying elements to impart special fabrication or performance characteristics for the sake of manufacturability and desired mechanical properties. The 6xxx series alloys have both magnesium and silicon as their main alloying elements, which combine as magnesium silicide (Mg2Si) following solid solution [1]. Alloys in this series are heat treatable. This series of aluminium alloys can be divided into soft alloy and hard alloy (jargon used by production people to indicate the tensile strength of the alloys, soft alloy has maximum tensile strength 215 MPa, while hard alloy has maximum tensile strength 310 MPa). Examples of soft alloy are 6063, 6061 and 6463, while the hard alloy encompasses 6061, 6005A and 6082 for the most common applications in consumer products, architectural structures and construction. **Figure 1** indicates

#### **Figure 1.**

*6xxx series alloy types and their Magnesium and Silicon weight percentages.*

the category of 6xxx series alloys according to their silicon and magnesium contents, which corresponds to their mechanical properties.

The 6xxx series alloys are especially suitable for hot extrusion process because of its extrudability to form solid or hollow/semi-hollow cross sections. The alloys are also heat treatable with artificial aging process to achieve the desired tensile strength, yield strength and elongation. There are a number of reasons why the 6xxx series are popular for various applications in extruded profiles, as stated below [2]:


### *Quality Assurance of Aluminium Extrusion for 6xxx Series Alloys DOI: http://dx.doi.org/10.5772/intechopen.109188*

In this book chapter, the focus is on conventional direct hot extrusion process. The word "hot" is referring to the preheating of the billet before the direct extrusion process. The basic process consists of forcing a preheated billet of round shape which is loaded into a container by a hydraulic ram with dummy block at its front end. The ram is linked to the main piston of a main cylinder powered by hydraulic system [3]. The aluminium billet can be preheated from 400 to 500°C in a preheat-oven designed with 3–4 heating zones. The temperature settings are in increasing trend from inlet zone to outlet zone. The billet will be forced to squeeze through a die which is also preheated to about 450–480°C to form a uniform cross-section profile either in solid, hollow or semi-hollow shape according to specific product design. The extruded profile will be subjected to air- or water-cooling process according to its temper requirements [4]. The run-out table on which the profile is placed is installed with cooling fans to blow the profile for continuous cooling process until it is stretched to straighten the material in the long length (ranging from 20 to 40 m). The stretching process also serves to impose strain hardening effect on the material for subsequent effective natural and artificial aging to achieve the desired mechanical properties. The stretched profile will be moved by conveyor to the cutting station to be cut into the desired order length (with tolerance of ±5 mm) and the material will be loaded into trolley and stacked into layers separated by spacer bars.

## **2. Defects in extrusion**

Aluminium alloy in extruded form is easily subject to damage due to external forces because the surface is relatively soft and requires extra precaution to prevent the unwanted damage that can cause the extruded profile deemed to be a reject (unacceptable product that does not fulfil standard or customer specifications). The defects in extrusion can be caused by multiple factors in the process related to the 4Ms in root cause analysis technique, namely man, machine, material and method. There are four main reasons that contribute to the defect's formation in the extruded products [5].


A local extruder from Malaysia (company's name is not to be disclosed) is willing to share with the authors the extrusion rejection data from Jan till Sept 2022. The data is shown in **Figure 2**.

The top 10 defects in extrusion in descending order are dented surface, bubble/ blister, tearing, scratches, die broken, water mark, streaking line, shape out, backend defect and soda mark.

## **Figure 2.**

To ease understanding, each of the defects are briefly explained below and illustrated with pictures.


**Figure 3.** *Dented mark on extrudate.*

**Figure 4.** *Bubble or blister appearing on extrudate surface.*

**Figure 5.** *Tearing.*


**Figure 6.** *Scratches.*

**Figure 7.** *Die broken.*


*Quality Assurance of Aluminium Extrusion for 6xxx Series Alloys DOI: http://dx.doi.org/10.5772/intechopen.109188*

**Figure 8.** *Water mark.*

**Figure 9.** *Streaking lines.*

> The basic cause of this streaking is a difference in microstructure between the streaked portion of the extrudate surface and the remainder, which leads to a difference in response in etching and anodizing.

viii.**Shape out**. Basically, it is dimension out of spec, linear or angular dimension, **Figure 10**. This is more inclined to happen on hollow profiles than solid profiles. Deflection of mandrel due to high pressure is one of the major causes.

**Figure 10.** *Shape out.*


**Figure 11.** *Backend defect.*

**Figure 12.** *Soda mark.*

## **3. Customer's requirements for extrudates**

As an extruder who is highly reputable for its quality products that can meet the requirements of global customers with competitiveness in quality, delivery and after-sales service, the company is used to gaining the customer's confidence and provide quality assurance by signing agreement with customer for the high volume of orders received. The agreement entrusts the company to manufacture and deliver the aluminium profiles all according to the terms and conditions contained in the agreement. The company must be ISO 9001 certified and undertakes to manufacture the products in strict compliance with all provisions of the agreement signed. Therefore, it is necessary for the manufacturer to understand the quality requirements of the customer thoroughly and execute effective quality management system to fulfil the requirements to ensure customer's satisfaction is achieved to secure long term business relationship.

The extruded products can be categorized into three main categories, namely mill finish profiles, powder coated profiles and anodized profiles. In this chapter, the focus is on mill finish profiles. The mill finish profiles to be used in painting and anodizing applications are required to comply with standards EN 12020-2, EN 755 and EN 573. The dimensional, mechanical and surface aspect requirements are usually specified in the product drawings and quality documents provided by customers.

Aluminium profiles are not only meant to work as structural support, but more importantly they are also for decorative purpose. Therefore, cosmetic criteria for surface of the profile are very important. The surface inspection can be categorized into three types:


• Non-visible—Non visible surface which is hidden from normal observation angle.

Typical surface defects characteristics are listed in **Table 1** with their inspection criteria.

Every extruded profile has a specific material specified in the drawing. The correct material must be used (e.g. 6063) and its chemical compositions must be verified by spark test (using arc/spark optical emission spectrometry (OES) analyser). The chemical compositions must comply with EN 755-2 or ASTM B221-14. The customer has the right to cut sample from the delivered lots and send to a third-party laboratory to verify its chemical compositions. Dispute will arise if the compositions vary from the results stated on the mill-cert of supplier. In that situation, the sample will be sent back to supplier for inhouse testing and another third-party testing.


#### **Table 1.**

*Extrusion surface defects characteristic.*

### *Quality Assurance of Aluminium Extrusion for 6xxx Series Alloys DOI: http://dx.doi.org/10.5772/intechopen.109188*

Mechanical property is an essential requirement of the extruded profiles. The specifications of mechanical property can be found in EN 755-2 or ASTM B221-14. Usually, the supplier has to possess a calibrated static tensile test machine of 100 kN capacity to do the test internally. On special request, the test can be done externally by a certified test service provider and certified test report is produced. The test results will be included in the mill-cert of the product. Usually the ultimate tensile strength, yield strength and elongation will be reported to qualify the product. The test specimen's dimensions must follow international standard such as that specified in ASTM B557M-15. The mechanical property is related to the temper of the alloy. 6xxx series aluminium alloy is heat-treatable. The correct process must be done to achieve the desired temper. When the products are supplied for marine applications, the mechanical property requirements will have to comply with either Bureau Veritas (BV) Rules on Materials and Welding for the Classification of Marine Units NR216 or American Bureau of Shipping (ABS) Rules for Materials and Welding (Part 2). The standards have specific test specimen's dimensions different from that of ASTM. The tests required to do include tensile test and drift expansion test (to test compression strength). The most common materials used for marine applications are 6061-T6 and 6082-T6.

Dimensional tolerances of the extruded profiles are critical to meet the customer requirements as first priority. Malaysia's extruders are used to following the JIS H 4100 standard for dimensional tolerances. The standard provides clear guidance on linear length, angle, straightness, flatness and twist. Advanced measuring machine like Romidot Vision H300 is used to measure the linear and angular dimensions of the profiles. The profiles have to be cut and deburred before measurement. Measurement of straightness, flatness and twist has to be done on a granite measuring table that has to be calibrated for levelling.

Quality can be defined by the degree of consumer satisfaction where the products are produced according to all technical specifications stipulated on drawings and customer-supplier quality agreement. Quality is also considered as faultless products where fewer defects is equivalent to lower costs. Hence, to satisfy customer needs and ensure product delivery according to their requirements, it is necessary to find solutions to overcome quality issues by gathering information about the entire production chain, analysing it, and making better decisions to implement continuous improvement by using PDCA methodology. It can help companies improve their operational efficiency and overall product quality [6].

## **4. Quality assurance activities in extrusion**

The company is specialized in the development and production of aluminium profiles for applications in engineering, architectural and industrial works in general. The products are supplied to local market and also to global market in South East Asia, North America, Europe and Australia. The company's quality policy is aimed at absolute customer satisfaction with punctual delivery and meeting the product functional requirements. The company's pursuit of excellence is a constant pursuit to strengthen business relationship, committed to developing and continuously improving the product quality and satisfactory after sales service. Therefore, Quality Management System (QMS) is its central pillar and various quality assurance activities have to be planned and implemented systematically to achieve the quality objectives. The following sub-sections will elaborate activities that have been implemented in the production system to ensure the right product quality at the right cost.

## **4.1 Control plan**

A control plan describes the methods for controlling product and process variation in order to produce quality parts that meet customer requirements. Control plans are a critical part of the overall quality process. They are living documents that are updated as processes change and improve throughout the product lifecycle [7]. The product control plan consists of process flow in its second column; therefore, it is also considered as process control plan incorporated. The control plan is designed specifically for a customer who has stringent quality requirements and they will conduct supplier audit to confirm that their products have product/process control plan to ensure good quality. Technical specifications are specified in the control plan which include process parameters, QC inspection criteria and chemical compositions. Control points are the location where measurement is done and specific equipment is listed. Related document or record is also specified and responsible persons are stated. **Figure 13** shows an extracted example of control plan (specific data is obscured for confidential purpose).

## **4.2 FMEA**

Failure Mode and Effects Analysis (FMEA) is a guide to the development of a complete set of actions that will reduce risk associated with the system, subsystem, and component or manufacturing or assembly process to an acceptable level [8]. The FMEA concerned here is Process FMEA (PFMEA) which is used to analyse the already developed or existing processes. PFMEA focuses on potential failure modes associated with both the process safety/effectiveness/efficiency, and the functions of a product caused by the process problems. PFMEA is a structured approach designed to achieve the following objectives:

• Predict failures and prevent their occurrence in manufacturing and other functional areas that generate defects.


**Figure 13.** *Product control plan.*


A partially extracted example of PFMEA for extrusion process is shown in **Figure 14**.


**Figure 14.** *Extrusion FMEA.*

## **4.3 Preventive maintenance**

The extrusion process is a heavily mechanical process involving the extrusion press machine and other accessories that construct the whole extrusion line. Poor preventive maintenance will cause extensive unscheduled downtime and reduce productivity. Bad condition of machine and accessories will also cause quality problem. The extrusion run-out table is mainly consisting of roller and belt conveyor. The fibre material of the roller and belt are subject to wear and tear after some time. The aluminium profiles are inevitably touching with the roller and belt during material handling process. Poor surface of the fibre material will cause scratches on the aluminium profiles. Therefore, the roller and conveyor belt must be changed whenever the surface has deteriorated. The extrusion press consists of many hydraulic cylinders as its major mechanical force. Oil leakage is a major issue and weekly inspection must be done on the main cylinder, side cylinders, container cylinders and shear cylinder. The line filters for servo control and oil cooler must be changed periodically before they are clogged. The shear blade of extrusion press that cut the butt end and the shear blade of billet preheat oven must be replaced when the blades are blunt. The water volume and pressure of the cooling chamber (usually mist spray at high pressure) must be inspected to be working in good condition because effective cooling is important to T6 tempered products. Rough saw cutting station must be maintained to be free of chips sticking to the conveyor belt and roller to prevent scratches. Operators are asked to always blow the chip off and do thorough cleaning every end of shift. **Figure 15** below shows the good vs. bad conditions in a typical extrusion press.

## **4.4 Material handling**

Aluminium surface is fragile and susceptible to scratched and dented damages when handled improperly. The extruded profile is long ranging from 20 to 40 m.

**Figure 15.** *Good vs. bad conveyor.*

**Figure 16.** *Good vs. bad materials stacking on conveyor table.*

Due to asymmetric contraction after cooling the profile tends to be in banana shape on the cooling table. Such a long profile needs two operators to handle at both ends. However, sometimes the operator handles it alone at one end, he will flip the profile and drag it on the belt conveyor surface, and this inclines to cause scratches and dented marks on the profile. When the operators are doing stretching, they have to carry the profile to the stretcher clamping platform, they are not able to lift up the profile from the table but to drag it for positioning and damages will be incurred if the handling is rough. Therefore, the supervisor and line leader are instructed to train their operators to do proper material handling on the conveyor table. The profiles must also align with proper distance in between them on the conveyor table to prevent knocking each other. **Figure 16** shows an example of the improper material handling and arrangement on the conveyor table that prone to cause damages.

## **4.5 8D report**

Defects detected in the shipment lots to customer will trigger "general customer complain report" (GCCR) if a single profile records a defect of 2% out of the total delivered quantity. QA department is responsible to answer the GCCR in 7 days after confirmation of the defects by sales department. The QA engineer has to investigate the complaint by requesting physical sample from customer (for testing purpose) or high-definition pictures. Based on the basic information of sale order no and delivery no, the QA engineer will extract data from SAP system to obtain the information of delivery date, manufacturing date (extrusion, anodizing, powder coating, fabrication or packing), alloy type, surface finishing specification, aging report and QC inspection report. The QA engineer will then do root cause analysis and fill in the 8D report in the GCCR reply form. The 8D report consists of 8 sections of team members, problem description, containment action, define the root cause, implement the corrective actions, implement the horizontal corrective actions, and verify effectiveness

of actions and preventive actions for recurrence. Sometimes, the company will send QC inspectors to customer's premise to do sorting or rework. If the reject quantity is huge, materials might be sent back for rework or scrap. The practice of 8D report will be recorded to the drawing file of the profile to alert the production and QC inspector of the complaint so as to take precaution in manufacturing and inspection process in

**Figure 17.**

subsequent orders to prevent the recurrence of defects. The drawing file is uploaded in the server and the production and QC staff will always access to the latest copy of drawing to check historical customer complaint record when that particular profile is being extruded. An example of 8D report is shown in **Figure 17**.

## **4.6 Quality campaign**

The company has launched a quality campaign with the objective to cultivate quality awareness among the employees to achieve the company's goals of quality products, excellence of services and on-time delivery as the cornerstone of promoting quality culture. Quality campaign involves top and medium management to disseminate some ideas to the workers to help them enhance their quality awareness. One of them is to "look-think-act". When a worker sees something abnormal, he has to think why it happens so? And to take action to do something right. The worker should not be ignorant of what is happening around him. He has to be always concerned about the machine is running properly, process parameters are correct, quality of products are good with minimum rejection, workplace is in proper 5S condition etc. Workers are taught to understand that quality is everyone's responsibility. Quality does not happen by chance; it is the outcome of coordinated efforts from all people involved in the process. Do not finger pointing but to work together for solutions whenever there is problem. After launching the campaign, the campaign committee conducted 5S audits at extrusion, anodizing, powder coating and fabrication departments. Research has shown that 5S is able to improve productivity and quality. Top winner of 5S of the

**Figure 18.** *Quality with integrity.*

workstation's workers will be given certificate of appreciation, souvenir and free meal coupon. Banner and poster of quality campaign are printed and displayed at many places in office and production areas. The slogan of the quality campaign is "Quality with Integrity", **Figure 18**.

## **4.7 Training**

Aluminium extrusion is a process that requires comprehensive knowledge to understand the critical success factors that contribute to quality and productivity. The workers are not solely required to do labour intensive job but also to understand many technical aspects of the process and product. They have to understand the importance of process parameters like billet preheat temperature, die preheat temperature, die exit temperature, container temperature, ram speed, extrusion cooling rate and stretching rate. The billet quality and its impact on product's metallurgy and mechanical properties have to be understood also. The QC inspectors must be able to identify all extrusion defects and have some basic knowledge of the possible causes of defects. The QC inspectors play an important role to verify defects and instruct production to stop and change die whenever necessary to prevent over-production of defective products. The QA department has taken initiative to write a QC Handbook for all QC inspectors to understand and practice. The handbook also serves as a training material to new staff. The company also conducted internal and external training for engineers on the topics of leadership, root cause analysis and problem solving, ISO9001 QMS Awareness, Report Writing Skills, etc.

## **4.8 Extrusion process parameters control**

Hot extrusion is a thermal deformation process done on the solid phase of billet. The management of temperature is significant to the extrusion quality and also productivity. Different alloys of billet must be preheated according to their individual upper limit temperatures. An empirical guideline is given in **Figure 19**, quoted from ASTM B807M-06. The extrusion speed is dependent on the billet temperature. The billet temperature is controlled by setting the temperatures of heating zones in the billet preheat oven. There is a region where we aim to achieve so we can maximize the extrusion efficiency as indicated in **Figure 20**. The die exit temperature is also very important because overheating will cause tearing defect on the surface due to localized melting spot when the material passed through the bearing surface; while lower exit temperature will cause insufficient cooling slope and hence inferior


#### **Figure 19.** *Extrusion billet temperature high limits.*

*Quality Assurance of Aluminium Extrusion for 6xxx Series Alloys DOI: http://dx.doi.org/10.5772/intechopen.109188*

#### **Figure 20.**

*Extrusion speed and billet temperature windows. Courtesy R. Peris.*


#### **Figure 21.**

*Extrusion die exit temperature and cooling rate.*

mechanical property. If it is T6 tempered material, minimum cooling rate has to be achieved to obtain the desired tensile and yield strength after artificial aging. The ASTM B807M-06 provides guideline on exit temperatures and cooling rates for different alloys as shown in **Figure 21**. The die exit temperature can be monitored by installing Infrared Radiation (IR) pyrometer at the machine as shown in **Figure 22**. Die exit temperature is correlated with billet preheat temperature and extrusion ram speed. These two parameters will be controlled by the operators to achieve the desired die exit temperature which is monitored in real-time by the IR pyrometer.

#### **4.9 7S Lean workplace**

The company is promoting the awareness of 7S lean workplace. 7S is defined as sort (seiri), set in order (seiton), shine (seiso), standardize (seiketsu), sustain (shitsuke), safety and spirit. It is a combination of Japanese 5S with two new elements of safety and spirit. The objectives of 7S are:


It is believed that a company that cares for its employee's safety will truly care for the product quality of its customers. An unsafe workplace will incur threat of life and stress of mind on the workers and cause disruption on their performance. Quality and productivity both suffer when employees are under stress, unsatisfied, or unable to complete their mission due to injury. But when the workplace is safe, it frees up employees to focus on their quality and their productivity. The 5S Method is a standardized process that when properly implemented creates and maintains an organized, safe, clean and efficient workplace. Improved visual controls are implemented

**Figure 22.** *Extrusion billet infrared temperature recorder.*

as part of 5S to make any process non-conformance obvious and easily detectable [9]. Spirit refers to cultivating the interest and passion in 7S through audit, competition and reward; also to strengthen the spirit of team work among workers from top to down. The audit on safety and 5S will be conducted continuously for one week in the department and score will be given to the outcome of audit. The top scorer will be announced and presented with honorarium and certificate of appreciation.

## **5. Conclusions**

The product quality of 6xxx series aluminium extrusion is dependent on multiple factors in the whole process stream. There are technical and management aspects that play the equivalent importance in ensuring quality and customer satisfaction. The production and QC teams must first be able to identify the extrusion defects correctly and do segregation of defects to prevent them from flowing to downstream process and wasting resources to process defective materials. PFMEA is important to guide production and maintenance team to take appropriate actions to prevent suboptimal process that will contribute to generating defects. There is sufficient knowledge base to determine the correct process parameters especially the temperature settings and control. The process must be stabilized within the controlled windows and operators must be trained to respond to anomaly in process by taking immediate actions to stop process and investigating the root cause to prevent continuous generation of defects. Historical data shows that the top five defects always dominated by scratches and dented damage which are due to improper material handling on conveyor table and trolley stacking. Intensive education and training have been provided to workers to improve their material handling. Quality can be viewed as a culture to cultivate in the workers. The company has taken initiative to launch quality campaign and 7S lean workplace campaign to promote the awareness of quality and importance of safety and housekeeping on product quality, productivity and morale. It is very important to cultivate the attitudes of continuous improvement and lifelong learning because we should not feel complacent with our current achievement and forget to make changes to cope with emerging challenges coming in our way. The extrusion industry has to grow and prosper in a sustainable manner with the commencement from optimizing its internal manufacturing process to improve quality, efficiency and reducing waste.

## **Author details**

Ying Pio Lim\* and Heng Kam Lim PMB Aluminium Sdn Bhd, Kapar, Malaysia

\*Address all correspondence to: limyp@pressmetal.com.my

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

## **References**

[1] Zolotorevsky VS, Belov NA, Glazoff MV. Casting Aluminum Alloys. 1st ed. Oxford: Elsevier; 2007. p. 45

[2] Misiolek WZ, Kelly RM. Extrusion of aluminum alloys. In: ASM Handbook, Metalworking: Bulk Forming. Vol. 14A. Materials Park, Ohio: ASM International; 2005. pp. 522-527. DOI: 10.1361/ asmhba0004015

[3] Pradip S. Aluminum Extrusion Technology. 1st ed. US: ASM International; 2000. pp. 1-3

[4] Uzun O, Rajendrachari S. Fundamentals of Materials Engineering—A Basic Guide. 1st ed. U.A.E: Bentham Science Publishers; 2021. DOI: 10.2174/97898114892281210101

[5] Arif AFM, Sheikh AK, Qamar SZ, Raza MK, Al-Fuhaid KM. Product defects in aluminum extrusion and its impact on operational cost. The 6th Saudi Engineering Conference, KFUPM Dharan. 2002;**5**:137-154

[6] Shamanth B, Prakash H, Subramanyam SS, Yogesh HK, Veerabhadrappa, Aravindrao MY, et al. Study of defects in aluminium extrusion process and evaluation by using quality tools. International Journal of Scientific and Engineering Research. 2021;**12**(7):355-366

[7] Hartwell J. Process Control Plan [Internet]. 2019. Available from: https:// www.iqasystem.com/news/control-plan

[8] Juran. Guide to Failure Mode and Effect Analysis—FMEA [Internet]. 2018. Available from: https://www.juran.com/ blog/guide-to-failure-mode-and-effectanalysis-fmea

[9] Quality-One. 5S Methodology [Internet]. 2022. Available from: https://quality-one.com/5s

## **Chapter 4**

## Low- and High-Pressure Casting Aluminum Alloys: A Review

*Helder Nunes, Omid Emadinia, Manuel F. Vieira and Ana Reis*

## **Abstract**

Low- pressure casting and high-pressure casting processes are the most common liquid-based technologies used to produce aluminum components. Processing conditions such as cooling rate and pressure level greatly influence the microstructure, mechanical properties, and heat treatment response of the Al alloys produced through these casting techniques. The performance of heat treatment depends on the alloy's chemical composition and the casting condition such as the vacuum required for highpressure casting, thus, highlighting the low-pressure casting application that does not require a vacuum. The level of pressure applied to fill the mold cavity can affect the formation of gas porosities and oxide films in the cast. Moreover, mechanical properties are influenced by the microstructure, i.e., secondary dendritic arm spacing, grain size, and the morphology of the secondary phases in the α-matrix. Thus, the current study evaluates the most current research developments performed to reduce these defects and to improve the mechanical performance of the casts produced by low- and high-pressure casting.

**Keywords:** aluminum alloys, low-pressure casting, high-pressure die casting, microstructure, mechanical properties

## **1. Introduction**

Low-pressure casting (LPC) involves feeding the molten material, typically a light metal alloy such as aluminum or magnesium, into the mold cavity by applying a gas pressure onto the melt surface. This causes the melt to rise through a riser tube, placed in a crucible, and fill the mold cavity located above the furnace. This mold can be a permanent one (LPDC, low-pressure die casting) or made of sand (LPSC, lowpressure sand casting), affecting the solidification rate [1, 2]. This process can be applied to produce a vast range of components with complex geometries, such as wheels and engine crankcases [3]. Although this process requires a higher capital cost than gravity casting, it becomes more competitive by producing better-quality melts and castings with fewer defects, especially in small or medium series, which has greater production yield and allows the application of heat treatments, unlike other processes, such as high-pressure die casting [4, 5].

High-pressure casting is an established casting process for low melting temperature alloys representing about 60% of all castings used in the automotive industries. Due to its high pressure, only permanent molds can be used, and thus it is called highpressure die casting (HPDC). This process is characterized by a short process cycle and high productivity alongside the ability to produce parts with complex geometry, thin sections, and good surface quality. The major disadvantage of HPDC is the high cost of the equipment and dies. However, this can be compensated with production series above 5000–10,000 castings/year [6–8].

This book chapter mainly aims at comparing the process and metallurgical aspects as well as the mechanical properties of Al alloys produced by LPC and HPDC. Finally, some of the most recent developments in the casting process are discussed.

## **2. Metallurgy aspects of casting Al alloys**

The properties of Al-Si alloy castings are significantly influenced by several microstructure features, including secondary dendrite arm spacing (SDAS), bifilms, and porosities [9].

#### **2.1 Alloys**

Aluminum alloys used in casting are often Al-Si or Al-Si-Mg, series 4xx.x and 3xx. x, respectively. The presence of silicon is critical in these alloys, since it increases the melt fluidity and decreases the coefficient of thermal expansion, facilitating casting and improving mechanical properties. The quantity of silicon added to the aluminum depends on the casting process, regarding HPDC, because of the high solidification rate, silicon contents required are between 8 and 12%, whereas, in LPSC, silicon contents between 5 and 7% are typically used. Thus, the most used and researched alloy for LPC is the A356 alloy, also known as ISO AlSi7Mg0.3 whose chemical composition can be found in **Table 1** [2, 11].

**Figure 1** presents an overview of the mechanical properties obtained by various researchers of the AlSi7Mg0.3 alloy produced by LPC [4, 5, 12–18]. Most of these researchers applied the heat treatment T6 (solution heat treatment followed by water quenching and then artificial age hardening) with the aim of enhancing the mechanical properties. In this graph, Quality Index (QI) values are also represented. This index is calculated through eq. (1):

$$QI = UTS + d \* \log\_{10}(A \text{\textquotedblleft}) \tag{1}$$

where ultimate tensile strength (UTS) is in MPa, A% is the elongation, and d is a constant dependent of the alloy, and for the Al-Si-Mg system *d* it is usually 150 [19].

Regarding HPDC, the most widely used alloy is AlSi9Cu3(Fe) which is normally a secondary alloy, and the chemical composition of this alloy includes some Fe as shown in **Table 2**. The effects of the presence of Fe are discussed in the next sections.

**Table 3** represents some of the mechanical properties of this alloy defined in the standard NP-EN 1706 (2000) [10] and some results from different studies [20–22].


**Table 1.**

*Chemical composition of the AlSi7Mg0.3 (in wt.%) alloy requirements of the EN 1706 standard [10].*

**Figure 1.** *State of the art of mechanical properties of the A356 with T6 alloy produced by LPC.*


#### **Table 2.**

*Chemical composition of the AlSi9Cu3 (in wt.%) alloy requirements of the EN 1706 standard [10].*


#### **Table 3***.*

*Mechanical properties of the HPDC AlSi9Cu3(Fe) alloy*.

The biggest difference between the properties of LPC and HPDC is the elongation values, expecting lower values of elongation due to the effect of porosities. For the AlSi9Cu3(Fe) alloy, the QI can be calculated through eq. 2 [21]:

$$QI = \text{YS} + 2\mathbf{10} \* \log\_{10}(A\text{96}) + \mathbf{13} \tag{2}$$

### **2.2 Microstructures**

**Figure 2** illustrates the microstructure of the AlSi7Mg0.3 alloy produced by LPDC. The as-cast microstructure (**Figure 2 a** and **b**) consist of dendrites of α-Al with the eutectic phases formed in the interdendritic spaces. In this case, the eutectic is composed of fine Si particles distributed in Al resulting from the eutectic reaction. Finally, it is also possible to identify coarse dark Mg2Si particles (identified in the figure with red circles and arrows). As mentioned before, these types of alloys are normally

#### **Figure 2.**

*Microstructure of the alloy A356.2 produced by LPDC: (a) and (b) as cast state; (c) and (d) after solubilization and quenching; (e) and (f) aged state [9].*

submitted to a T6 heat treatment. The initial stages of solubilization (540°C for 6 h), quenching in water (at 40°C), and finally artificial aging (155°C for 200 min) resulted in a similar microstructure as before. However, the Si particles become coarser and more rounded, as shown in **Figure 2** f. With the increase in aging time and temperature, the UTS and yield strength (YS) tend to increase and elongation decreases due to the precipitation of very fine Mg2Si phases, which are not possible to observe by optical microscopy [9].

Concerning the HPDC parts, the microstructure is more refined than other casting methods due to the rapid filling and fast solidification. When observing the cross section of a cylindrical casting produced by HPDC, three zones with distinct microstructures can be identified: skin layer, segregation band, and central zone (in the opposite direction of heat dissipation). When the molten Al is inside the shot sleeve, the α-Al phase starts to nucleate and grow from the walls that are commonly referred to as externally solidified crystals (ESCs). During the filling process, these crystals are forced to the center zone; thus, the solidified microstructure in this zone is composed of several coarse dendritic ESCs with sizes larger than 10 μm. Inside the die cavity, the

### *Low- and High-Pressure Casting Aluminum Alloys: A Review DOI: http://dx.doi.org/10.5772/intechopen.109869*

α-Al phase continues to form however in small sizes, normally smaller than 5 μm. The high cooling rate of the melt due to the interaction with the cooler die cavity surface creates larger undercooling, promoting rapid nucleation of the α-Al phase and originating the skin layer. With ESCs continuously growing and partially interlocked during filling, liquid segregation between the central and skin zones is promoted and forms an inhomogeneous microstructure zone known as a segregation band. In this zone, the α-Al phase content is relatively low, and other phases, such as eutectic Si and intermetallic compounds, are present in larger quantities [7, 23–25].

### *2.2.1 Fe-rich phases*

Fe is the most prejudicial contamination of Al alloys. The incorporation of these impurities occurs mainly during the recycling process and is impossible to remove by conventional methods, such as pyrometallurgy. Fe tends to react with Al to form hard and brittle intermetallic phases with a wide range of chemical formulas, sizes, and shapes. The β-Al5FeSi is the most detrimental phase due to its plate-like shape that works as a stress concentration source and fragilizes the alloys. Recycled alloys, known as secondary aluminum alloys (SAAs), are mainly used in casting due to lower chemical restrictions needed in these processes when compared with wrought alloys. However, since the SAAs in the present recycling system is the last sink of the recycled Al alloys, a scrap surplus is expected to occur soon. Thus, it is necessary to enhance the applicability of these alloys by reducing the negative effects of the Fe-rich and obtaining SAAs with mechanical properties comparable to the primary alloys [26–28].

Even though in HPDC, the Fe can aid the ejection of the casting part from the die and prolong the die life by avoiding soldering between the two materials, and the brittle Fe-rich phases also negatively affect the mechanical properties of the alloys. In this process, the Fe-rich phases, specifically α-Al(Fe, Mn)Si can form as early as in the shot sleeve stage by nucleating in oxides from the melting furnace as Jiao et al. [24] reported in a study with AlSi10MnMg alloy. Two types of morphology were distinguished in this case, and the particles formed in the shot sleeve presented a shape like a hexahedron with a size of around 14 μm alongside the particles formed inside the cavity due to the higher cooling rate had smaller sizes, around 6 μm, with a spherical shape. In another study [7] using the same alloy, three different morphologies of the Fe-rich phase shapes were identified: polyhedral – a well-defined cube; fine compact – a claw-like shape; and Chinese script-type shape – similar to a compact skeletal structure. However, to the author's knowledge, only a few articles that study the effects of these phases on alloys produced by LPC or HPDC have been published. Thus, a more in-depth understanding of the process parameter effects on the formation of the Fe-rich phases is needed to enhance the applicability of the SAAs.

## **2.3 Defects**

The hydrogen pickup by the melt and the formation of defects such as bifilms are the two most severe issues in Al-casting. In the LPC process, the alloy is usually heated and melted under an inert gas flux, such as argon, excessive melt oxidation, and hydrogen pickup are minimized and may provide a cleaner melt. However, the material and all equipment must be dried to remove any moisture, and the slag must be removed before casting. Since it is possible to vary the casting velocity by altering the pressure supplied to the melt, this technique is distinguished by smooth filling and good feeding capabilities. An uncontrolled filling of the mold cavity provokes a melt

with high turbulence and promotes the entrapment of air. This turbulence also facilitates the molten metal to fold onto itself, which is unable to join due to the oxide layer and creates long and thin defects known as bifilms. These surfaceentrained defects have been shown as the primary factor for porosity formation in LPC [6]. As a result, it is critical to ensure many processes features in the mold design and casting methods, such as preventing "waterfall" effects, which occur when molten metal falls into a depression and providing a melt velocity in the mold cavity of fewer than 0.5 m/s. These are some examples of guidelines established by Campbell to limit the melt turbulence and the number of defects [3, 7].

In the HPDC process, it is commonly verified that scrap rates of 5 to 10% due to the occurrence up to 30 specific types of defects can occur. Some of the most common defects that have a direct effect on mechanical properties are gas porosity and oxide films, similar to LPC [6, 8, 29]. Other defects can occur when further processes are applied to HPDC parts, specifically heat treatment. The high pressure associated with this process creates a high quantity of entrapped gasses in the Al. These gasses are originated from the decomposition of the die lubricants and from the entrapped air during the injection. During heat treatment, especially due to the high temperatures of the solution treatment stage, the gasses expand forming the defect known as blisters turning the piece unsuitable to use. And thus, commonly the alloys produced by HPDC are considered as not heat treatable [30].

## **3. LPC and HPDC methodologies and processing parameters**

In this section, process cycles, working parameters, and recent advancements in LPC and HPDC are presented, as well as some effects of these aspects on the microstructure and mechanical properties of the alloys.

## **3.1 Equipment**

The equipment used in LPC and cold chamber HPDC is shown in **Figure 3**. A furnace, a mold – which may be composed of metal or sand – and a feeder tube – which lets the metal rise from the crucible to the mold cavity – are the most common parts of the equipment required for LPC. Whereas, a shot sleeve with a hydraulic operated plunger, an intricate, and costly metal die, as well as complex systems for mold fixing, part ejection, and die cooling are the main equipment components for cold chamber HPDC [32].

#### **3.2 Process cycle**

A comparison between the two process cycles of LPC and HPDC is represented in **Figures 4** and **5**, respectively. Some similarities can be observed which are mainly the stages of filling and solidification under pressure. LPC consists initially of melting the alloy inside the furnace used for casting or by the loading of already molten Al by a ladle. When the molten is prepared for casting, the feeder tube and mold are placed on top of the furnace. By applying gas pressure, commonly with Ar, the melt rises through the feeder tube and fills the mold cavity. The pressure is maintained during the solidification of the material inside the mold. When the pressure is released, the remaining molten material falls back into the crucible. The mold is then opened when *Low- and High-Pressure Casting Aluminum Alloys: A Review DOI: http://dx.doi.org/10.5772/intechopen.109869*

**Figure 3.** *General scheme: (a) LPC and (b) cold chamber HPDC (adapted from [31]).*

**Figure 4.** *General scheme of the LPC cycle [33].*

dies are used, or the sand mold is destroyed by vibrations. Finally, parts can be moved to post-processing, such as heat treatment and sand-blasting [33].

The HPDC cycle mainly includes five steps, as shown in **Figure 5**: spraying and closing of the die; dosing of molten Al into the shot sleeve; injection of the melt by the application of pressures between 7 and 140 MPa through a plunger; solidification under pressure; and the opening of the die and the ejection of the part. Then the part follows to post-process, such as trimming. Mostly, the die is clamped to securely close together the two halves of the die that are already attached to the casting machine with enough force to guarantee that the die does not open during injection of the molten metal or solidification. The surface of these dies must be clean and lubricated

**Figure 5.** *General scheme of the HPDC cycle. Adapted from [31].*

**Figure 6.** *Fluid velocity vector of the cylindrical riser tube (left) and the cone-shaped tube (right) [33].*

to facilitate the ejection of the parts. The molten Al that was previously transferred into a chamber and part of this is then injected into the die cavity [6].

## **3.3 Design of die for LPC**

One of the most recent studies about LPC is regarding the geometry design of the transition zone from the feeder tube to the mold cavity. While HPDC's most recent studies focus on applying a vacuum in the casting process.

Different numerical studies have been carried out to investigate the effects of geometrical parameters of the die design and the feeder tube. Yaki [33] evaluated the influence of cylindrical and cone-shaped riser tubes on liquid rising pressure and stability. The later geometry promotes a lower liquid pressure during rising and a more stable filling. This can be observed in **Figure 6**, which represents the velocity vector diagram of liquid at 10s of rising. In the case of the cylindrical tube, it is possible to observe a vortex inside the tube that increases the turbulence of the melt.

This does not occur with a conic riser tube allowing the melt to rise with more stability.

Bedel et al. [34] evaluated the impact of die geometry on filling dynamics through simulation and experimentation. Another study [35] observed that the horizontal section's geometric parameters of the furnace, the rising tube, and the mold cavity were responsible for oscillation during filling. According to specific geometric parameters studied, the section changes ratio and the section transition height impacted filling dynamics, concluding that the melt flow will be more unstable by applying greater pressure ramp and section change between the furnace and feeder tube. Thus, these researchers [34] aimed at designing an algorithm to be applied in LPC. This algorithm may be used to construct the filling system to find the proper filling pressure ramp for any complicated component. Some processes on this algorithm consist of determining the possible orientation of the parts, computation of the maximal vertical section change for each orientation, and selection of the orientation with the lowest corresponding value. It can be useful for the determination of the transition height (trans) and the actual section change (R) in a filling system to be used with a specific feeder tube. With the 3D map developed by Bedel et al. or any equivalent Lagrangian model, the maximal pressure ramp can be determined as a function of the R and trans-values. And thus, the maximum filling pressure ramp and the minimum filling system height can be determined for any component.

## **3.4 Vacuum-assisted HPDC**

Vacuum-assisted high-pressure die casting (VHPDC) has been studied with the main purpose of reduction of entrapped air and quantities of oxide films in the cast. This is done by applying a low atmospheric pressure in the shot sleeve and cavity during injection and filling [36]. With applying vacuum, some process parameters are altered, such as the filling time, which tends to be faster. In a simulation study, Kan et al. [37], employing 500 Pa of pressure and a melt speed of 1 m/s, verified that the mold cavity under vacuum was filled in 0.95 seconds whereas the filling process took 1.2 seconds in the non-vacuum study. These results for vacuum and non-vacuum real experiments were 0.6 and 0.8 s, respectively, thus, saving about 21% of the time cycle.

In **Figure 7**, it is possible to observe the microstructures of AlSi9Cu3(Fe) alloy produced by VHPDC. These images did not show any grain size deference from similar microstructures of alloys produced without vacuum, as shown in **Figure 8** from the same study [25]. The phases α-Al, eutectic Si, and Fe-rich phases also did not

#### **Figure 7.**

*Microstructure of the AlSi9Cu3(Fe) cast by VHPDC (a) skin layer; (b) central region; and (c) observation of micro-porosities [25].*

**Figure 8.**

*Microstructure of the AlSi9Cu3(Fe) cast by HPDC (a) at the surface; (b) central region; and (c) porosities defects [25].*

vary significantly with the usage of vacuum. Thus, the main differences were porosity levels and thus increased casting integrity. Reducing trapped air allows the application of heat treatment to the cast without causing the blister defects mentioned above [36]. The pores tended to be fewer and smaller, with a decrease in volumetric porosity, from 0.34 to 0.09%, and were distributed more evenly with VHPDC. This reduction in porosity enhanced the fatigue life (about 16%) of the alloy with a 4% increase in fatigue strength. The static tensile properties were improved slightly, especially UTS from 314 to 326 MPa and elongation from 2.11 to 2.81% [25]. In another study, Hu et al. [38] proved that increasing the vacuum levels can indeed improve the YS of the alloys with the reduction in pores volume.

In a study of the effect of T6 heat treatment on the alloy AlSi11MgMn, Liu et al. [39] observed a decrease in UTS, while the elongation increased for alloys produced by VHPDC. In this alloy, the microcracks formed near the large α-Fe intermetallic and not due to the eutectic Si particles. The heat treatment could change Si morphology from fibrous particles to more globular shapes. Thus, the type of fracture observed corresponded to a more ductile behavior than the fracture of the non-heat-treated alloy.

#### **3.5 Melt treatments**

In LPC, some processes should be performed on the molten alloy to guarantee good melt quality such as grain refinement and eutectic silicon modification to provide the desired mechanical properties. Grain refining of α-Al grains seeks to improve the alloys' mechanical properties, such as ultimate tensile strength and fatigue strength. It is commonly accomplished by adding B and Ti via master alloys, constituted by Al-Ti-B compounds, by the creation of Al3Ti and/or TiB particles as nucleation agents during solidification. Although the performance of the latter type is mostly reported, a recent study revealed the better performance of Al2.2Ti1B-Mg grain refiner. This master alloy leads to the growth of an Al2.2Ti1B-Mg layer on the TiB2 particles. Decreasing the mismatches between TiB2 and Al promotes the nucleation of α-Al and results in a higher efficiency refining process than the other master alloys [40].

Besides, the primary goal of silicon modification is to reduce the size and form of eutectic particles to increase elongation values. The eutectic silicon modification is also done by master-alloy additions containing specific elements, such as Sr. or Na,

*Low- and High-Pressure Casting Aluminum Alloys: A Review DOI: http://dx.doi.org/10.5772/intechopen.109869*

that force the nucleation of the eutectic silicon to occur after the formation of eutectic aluminum. The presence of these elements guarantees that silicon grows between these α-Al grains and acquires a fibrous morphology, and shorter length [41]. However, the effect of these additions on defect formation is not yet thoroughly studied, with several studies showing contradictory observations. Sr additions influence the number of bifilms and the size of the pores, whereas B stimulates the formation of defects in the castings' cores. Furthermore, the Sr combines with the Al2O3 to generate the spinel Sr.Al2O3, facilitating the oxides to break into smaller ones [4, 42, 43]. Therefore, the additions using master alloys are a significant step in the casting process to enhance the mechanical properties by modifying the microstructures of the alloys. Moreover, alloys modified and refined have been shown to present lower porosities and higher density values than alloys without these treatments [44]. To avoid excessive porosity originating from the dissolved hydrogen, normally degassing processes are carried out before casting. Several technologies can be applied to degas the melt such as rotor degassing with argon and ultrasonic melt treatment [45, 46].

### **3.6 Effects of process parameters**

In LPC, several parameters have a notorious effect on the properties and quality of the alloys. Some of these parameters include the mold material, the filling conditions, and the holding pressure (HP).

The type of materials used in the casting molds affects the cost and quality of the castings. Sand molds are typically less often used than permanent ones, and the use of dies allows higher productivity. However, compared to sand molds, this kind of mold requires a higher capital investment. The mechanical properties might also be impacted by the type of mold. The refined of α-Al phase, which exhibits smaller dendritic arm spacing, and eutectic Si particles in the metallic dies to induce higher values of UTS and elongation. This refinement is attributed to shorter solidification times [4].

Puga et al. [12] evaluated the effects of mold-filling parameters effects on the mechanical properties of an LPSC AlSi7Mg0.3 alloy. In this study, two different pressure-time curves were evaluated for two temperatures (650 and 700°C). The main difference in these curves is the number of ramps. While one curve only has two ramps, the other curve presents an intermediate third ramp which controls and reduces the filling velocity to smaller than 0.5 m/s. This last curve allowed a smoother filling with lower pressurized speed (Pa/s) and created a casting with fewer defects, such as porosities and oxides. And thus, the casting produced with a 3-ramp curve at 650°C presented the highest values of UTS (253 9 MPa), yield strength (YS = 215 5 MPa), and elongation (2.4 0.2%). These authors revealed that the application of ultrasonic degassing treatment promoted the refinement of the alloys. This treatment at the lowest temperature (650°C) provoked a more intensive grain refinement and a more globular microstructure and enhanced the mechanical properties.

The LPC allows solidification to occur under a certain pressure known as holding pressure (HP). Several researchers, for example, Timelli et al. [47] and Wu et al. [16], reported a relation between HP with several characteristics such as SDAS and porosity. The local cooling rate during solidification has an impact on SDAS, which is a commonly used aspect to determine the grain size in casting alloys. Smaller SDAS values indicate a more refined microstructure, which improves some mechanical

properties [48]. Timelli et al. concluded that by increasing HP from 35 to 50 kPa, the SDAS decreased from 67 to 58 μm and the porosity levels reduced from 0.3 to 0.1%. On the other hand, Wu et al. studied an even higher HP of 85 at 300 kPa. With the highest pressure, the researchers obtained SDAS values of 39 6 μm (for a cooling rate of 1°C/s) and 21 2 μm (for a cooling rate of 10°C/s). The density of the alloys also reached the highest values for these conditions. With the smallest SDAS and lowest porosity levels, the alloy solidified under the highest pressure and cooled faster, presenting the highest UTS value (293 11 MPa) and elongation (14 1%) of all the alloys studied.

It has been widely reported that the process parameters of HPDC affect the mechanical properties and microstructures of the alloys. Cho et al. [49] observed a strong proportional relationship between dendrite arm spacing and cooling rate. With the increase of the cooling rate from 15 to 100°C/sec, the dendrite arm spacing of AlSi9Cu3 and AlSi11Cu3 alloys reduced to more than half, from 12 to 5 μm and from 8 to 5 μm, respectively.

Santos et al. [50] observed no clear correlation between pressure (35 or 70 MPa) and injection temperature (579, 643, or 709°C) with the porosity of the AISi9Cu3(Fe) alloy produced by HPDC. Samples with 70 MPa have the lowest and highest values of porosity, 3 1 (579°C) and 5 1 (709°C). Moreover, these parameters had some effects on the microstructure of the alloys, specifically the α-Al phase. Higher temperatures promoted a refinement of this phase, while at lower temperatures the dendrite structure tends to be fragmented. The injection temperature seems to have no significant effect on mechanical properties, but the highest values of UTS were absorbed with the highest temperature (244 12 and 265 8 MPa, with 35 and 70 MPa injection pressure, respectively). The elongation values were constant, between 4 and 5%, in all alloys. However, no correlation between UTS and YS could be determined with these parameters. In another study of the same alloy, Obieka et al. [51] concluded that a higher pressure of about 140 MPa provoked an increase in all the mechanical properties of the alloy: UTS, YS, elongation, hardness, and impact strength. These results were mainly attributed to the refinement of the microstructure and the various phases.

## **4. Conclusions**

This book chapter allowed for some direct comparisons between low-pressure casting and high-pressure die casting, as follows:


*Low- and High-Pressure Casting Aluminum Alloys: A Review DOI: http://dx.doi.org/10.5772/intechopen.109869*

• Some of the most recent developments in both processes were analyzed. In recent studies, algorithms have been defined to establish rules for die design dies for LPC. In HPDC, applying a vacuum has been studied to improve some mechanical properties and to allow the application of heat treatments.

## **Acknowledgements**

The authors gratefully acknowledge FCT – Portuguese Foundation for Science and Technology (2022.11466.BD), the funding of Project AM2R – Agenda Mobilizadora para a inovação empresarial do setor das Duas Rodas (C644866475-00000012) and, Hi-rEV – Recuperação do Setor de Componentes Automóveis (C644864375-00000002), cofinanced by Plano de Recuperação e Resiliência (PRR), República Portuguesa through NextGeneration EU.

## **Conflict of interest**

The authors declare no conflict of interest.

## **List of abbreviations**


*Recent Advancements in Aluminum Alloys*

## **Author details**

Helder Nunes1,2, Omid Emadinia1 \*, Manuel F. Vieira1,2 and Ana Reis1,2

1 LAETA/INEGI, Institute of Science and Innovation in Mechanical and Industrial Engineering, Porto, Portugal

2 Faculty of Engineering of the University of Porto, Porto, Portugal

\*Address all correspondence to: oemadinia@inegi.up.pt

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Low- and High-Pressure Casting Aluminum Alloys: A Review DOI: http://dx.doi.org/10.5772/intechopen.109869*

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[44] Tunçay T. The effect of modification and grain refining on the microstructure and mechanical properties of A356 alloy. Acta Physica Polonica A. 2017;**131**(1): 89-91

[45] Puga H, Barbosa J, Seabra E, Ribeiro S, Prokic M. The influence of processing parameters on the ultrasonic degassing of molten AlSi9Cu3 aluminium alloy. Materials Letters. 2009;**63**(9):806-808

[46] Schmitz C. Handbook of Aluminium Recycling (2nd Edition) - Mechanical Preparation - Metallurgical Processing - Heat Treatment. Germany: Vulkan Verlag; 2014

[47] Timelli G, Caliari D, Rakhmonov J. Influence of process parameters and Sr addition on the microstructure and casting defects of LPDC A356 alloy for engine blocks. Journal of Materials Science & Technology. 2016;**32**(6): 515-523

[48] Li Y, Liu J, Zhou H, Huang W. Study on the distribution characteristics of microstructure and mechanical properties within the cylinder head of low-pressure sand cast aluminum alloy. International Journal of Metalcasting. 2021;**16**:1252-1264

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[51] Obiekea K, Aku S, Yawas D. Effects of pressure on the mechanical properties and microstructure of die cast aluminum A380 alloy. Journal of Minerals and Materials Characterization and Engineering. 2014;**02**:248-258

## **Chapter 5**

## Additively Manufactured High-Strength Aluminum Alloys: A Review

*Fahad Zafar, Ana Reis, Manuel Vieira and Omid Emadinia*

## **Abstract**

This chapter summarizes the recent advances in additive manufacturing of high-strength aluminum alloys, the challenges of printability, and defects in their builds. It further intends to provide an overview of the state of the art by outlining potential strategies for the fabrication of bulk products using these alloys without cracking. These strategies include identifying a suitable processing window of additive manufacturing using metallic powders of conventional high-strength aluminum alloys, pre-alloying the powders, and developing advanced aluminum-based composites with reinforcements introduced either by *in situ* or *ex situ* methods. The resulting microstructures and the relationship between these alloys' microstructure and mechanical properties have been discussed. Since post-processing is inevitable in several critical applications, the chapter concludes with a brief account of postmanufacturing heat treatment processes of additively manufactured aluminum alloys.

**Keywords:** additive manufacturing, high strength, aluminum alloy, advanced processing, challenges, defects, advanced composites

## **1. Introduction**

Additive manufacturing (AM) of aluminum (Al) alloys has found industrial applications and now has become a firmly established field. The number of research publications regarding Laser Powder Bed Fusion (L-PBF), one of the most popular AM processes, has shown an exponential increase during the last decade [1]. This trend is certainly not unpredictable, considering the prior wide industrial use of conventional Al-alloys due to their lightweight, high specific strength, and corrosion resistance. AM further broadens the horizon of applications for Al-alloys by its ability to produce complex geometric shapes with hollow sections for weight reductions [2]. The high-strength aluminum alloys (HSAAs) are particularly interesting in the aerospace and automotive industries. Special efforts have been directed at AM of HSAAs, and interesting advances have been made in this field [3, 4], especially in the last decade. Since the L-PBF technique has attracted the most research interest and shown promising results with HSAAs, most of the discussion and references made in this chapter will be focused on L-PBF of HSAAs, limitations in processing, strengthening

mechanisms, recent achievements, defects in printed materials, and possible strategies to overcome them.

Directed energy deposition (DED) [5] and wire arc additive manufacturing [6] processes have also been utilized for the manufacturing of HSAAs. Since DED offers freedom from restriction to use a closed chamber and offers the possibility of printing large structures, a brief review of DED of HSAAs is presented in this chapter.

## **2. Laser powder bed fusion of aluminum alloys**

Most of the foundry alloys, especially those designed for casting with near-eutectic compositions, are readily printable with negligible risk of cracking, sufficient fluidity, and minimal hot tearing susceptibility (HTS). These favorable characteristics have attracted immense research interest and led to accelerated development in AM of Al-Si alloys. But these alloys could only achieve a low-medium yield strength of <300 MPa. In contrast, some wrought alloys (2xxx, 7xxx series) can achieve far higher (300–500 MPa) yield strength. However, these alloys have not been found readily printable by L-PBF [7, 8].

## **2.1 Limitations in processing**

The L-PBF production of HSAAs faces challenges such as characteristic columnar microstructure eventually promoting hot cracking susceptibility (HCS) [9, 10], wide solidification range [11], solute loss due to evaporation [12], limited scanning speed to avoid cracking [13], balling, oxidation, and gas porosity.

Columnar grain growth is typically observed in L-PBF processing of Al-alloys due to the direction of the maximum thermal gradient [14]. In addition, for a certain set of L-PBF process parameters, multiple ratios of temperature gradient (G) and growth rate (R) may exist in the melt pool favoring columnar growth (either in cellular, planar, or dendritic mode). This columnar growth, more specifically the cellular or dendritic growth, leads to poor strain accommodation, and degraded liquid permeability eventually leading to high HCS [15] as shown in **Figure 1a–f**.

**Figure 1.** *(a–f) Solidification cracking observed in AlMg4.5Mn0.7 (re-printed from [16]).*

## *Additively Manufactured High-Strength Aluminum Alloys: A Review DOI: http://dx.doi.org/10.5772/intechopen.109697*

HSAAs tend to have a wide solidification range (or freezing interval), which results in diminished backfill of liquid between coarse columnar crystals [17]. Solute loss occurs due to high processing temperatures during L-PBF, lower boiling points of certain alloying elements and their associated higher equilibrium vapor pressures (than that of aluminum). **Table 1** gives numerical figures for the evaporation of Zn and Mg in three different Al-alloys during L-PBF [12].

In metal deposition during additive manufacturing, liquid metal may not wet the impinging layer (or substrate) due to the surface tension of the liquid. To minimize the surface energy, the deposited liquid metal takes a spherical shape, termed *balling* (see **Figure 2a**).


#### **Table 1.**

*Solute element concentration before and after L-PBF [12].*

#### **Figure 2.**

*(a–i) Micrographs of selective laser-melted AZ61 magnesium alloy under different laser scanning speeds showing balling and porosity defects (re-printed from [18]).*

Being highly reactive toward atmospheric oxygen, aluminum alloys tend to oxidize readily by reaction with a small quantity of oxygen trapped in the air gaps between aluminum powders, which causes inferior quality in L-PBF deposited HSAAs [19].

Porosity defect has been widely reported as well as investigated in Al-alloys, and a porosity of 0.5% is generally termed acceptable in AM Al-alloys [20]. Insufficient melting of powder (or lower than the optimum volume energy density of laser) [21], moisture absorption in Al-powder from the atmosphere [21], spatter and smoke formation during AM process [22], and use of helium as inert gas for the process [23] can increase the porosity of resulting AM product.

## **2.2 Trends in the elimination of defects**

Continued efforts have been made in the past decade to over the problems discussed above. Broadly, three main strategies have gained particular attention, showing promising results with HSAAs. These strategies are briefly listed below, and a discussion of their application and limitations will follow:


Though designers prefer to utilize existing materials with sufficient reliable property data, it should be kept in mind that even well-established alloys present a significantly different microstructure after additive manufacturing due to rapid thermal processing. While in the previous discussion, three different strategies are presented for the elimination of defects in HSAAs, there is some overlap in these strategies to achieve an acceptable set of properties in the AM HSAAs. Moreover, there are several interdependent factors that affect the printability and the quality of the final AM product, which cannot all be discussed at length here, provided the scope of this text. **Figure 3** presents these factors, stemming either from the raw materials or the AM processing strategy.

### **2.3 Grain refinement strategy**

The addition of nucleating agents to achieve the heterogeneous nucleation of aluminum grains upon the potent primary particles is utilized for grain refinement in *Additively Manufactured High-Strength Aluminum Alloys: A Review DOI: http://dx.doi.org/10.5772/intechopen.109697*

**Figure 3.** *Factors influencing the properties in additively manufactured HSAAs.*

HSAAs. The heterogeneous nucleation promotes the formation of equiaxed grains. Such grain refinement leading to equiaxed grains is highly desirable as it offers benefits, such as reduced susceptibility to hot tearing, higher strength, lesser anisotropy, and shrinkage porosity.

A consequent reduction in the fraction of columnar grains enhances the printability of HSAAs. For equiaxed growth of a crystal, heat must dissipate from the crystal to melt (G < 0) [24]. In contrast, during L-PBF, heat dissipates from the melt to crystals and onward down to the substrate (G > 0). Thus, high enough undercooling is required to promote equiaxed grain growth. The heterogeneous nucleation diminishes the nucleation barrier by facilitating the growth of Al matrix crystals on preexisting nuclei that have a small lattice parameter misfit with that of the matrix [25]. As the growth of equiaxed grains progresses on nuclei, they impinge upon the neighboring equiaxed grains as well as the growing columnar grains, which restrict columnar growth. This phenomenon is termed as "columnar to equiaxed transition" (CET) in the solidification processing literature. The reduction in columnar grain growth also reduces the crack susceptibility in the AM HSAAs, which is a common problem faced during L-PBF of conventional wrought aluminum alloy grades.

The transition metal Scandium (Sc) and Zirconium (Zr) have best served this purpose [26, 27]. Sc provides exceptional grain refinement in aluminum alloys. The primary Sc-containing particles serve as heterogeneous nuclei, which can mitigate solidification cracking. Sc alloying imparts a significant precipitation hardening in aluminum alloys, though it is limited by the solid solubility of Sc (0.4%) in aluminum. However, rapid solidification rates in the L-PBF process enable the retention of as

much as double this quantity in solution, which can be precipitation strengthened by nano-Al3Sc precipitates during subsequent ageing treatment at 250–300°C [28]. Sc also restricts grain growth in aluminum alloys since Al3Sc dispersoids serve to pin the grain boundaries and stabilize the grain structure [29]. These Al3Sc particles have a small mismatch of lattice parameter with that of the aluminum matrix (0.4103 nm vs 0.4049 nm), which makes them highly effective nucleation sites for α-aluminum grains. In aluminum alloys, every 0.1% wt. Sc provides a 40–50 MPa increment in yield strength. This increase results from the precipitation strengthening by the formation of L12 coherent precipitates (Al3Sc) during aging heat treatment [30]. Upon further addition of transition metals with low diffusivity in aluminum, such as Ti, Zr, and Hf can partially substitute Sc atoms forming precipitates such as Al3Sc1–xZrx. These resulting precipitates are highly resistant to further coarsening due to coreshell-like structure, and they offer a further advantage of high-temperature stability (aged at 325°C) [31] as compared with precipitates of conventional precipitationhardened aluminum alloys (typically aged 120–190°C). However, Sc has been identified as a critical raw material by European Commission [32], and alternates must be explored to offer a competitive advantage.

In an Al-Zn-Mg-Cu-Ta alloy, Ta forms*in situ* primary Al3Ta particles and can dissolve in the second phase Al2Cu to restrict further coarsening during heating cycles [33].

**Figure 4** presents the tensile yield strengths achieved in state-of-the-art HSAAs bearing Sc and Zr, which clearly shows a possibility to achieve a yield strength higher than 500 MPa with an acceptable ductility.

Though it is worth mentioning here that multiple strengthening mechanisms may play role in strengthening, with the dominance of one or the other mechanism in the case of a particular HSAA (for further insight into strengthening mechanisms, see Ref. [34]).

### **2.4 Eutectic strategy and narrowing down the freezing range**

Eutectic strategy is more commonly applied in L-PBF of Al-Si alloys, which facilitates sufficient backfilling of cracks. The terminal stage of solidification [35] is

**Figure 4.** *Tensile yield strength (95% confidence mean) of recent Zr, Sc-strengthened HSAAs.*

### *Additively Manufactured High-Strength Aluminum Alloys: A Review DOI: http://dx.doi.org/10.5772/intechopen.109697*

considered a stage with the highest hot cracking susceptibility. The conventional wrought high strength age-hardenable alloys (2xxx, 7xxx) contain alloying elements, which tend to widen their solidification range, leading to the segregation of low melting point phases during grain growth [36]. The solidification range is defined as the difference between the liquidus and solidus temperatures of the alloy. Inspired by the excellent printability of Al-Si alloys, researchers were tempted to use Si as an additive to the metal powder of existing wrought aluminum alloys. Pre-alloying with 3.74 wt.% Si reduced the freezing interval and eventually decreased the solidification cracking susceptibility in modified Al-7075 [37]. In another study, ultimate tensile strength and yield strength of 548 and 403 MPa were achieved in a newly designed alloy with Si alloying wherein numerous Al-Mg2Si fine eutectics were formed in situ upon L-PBF, which helped mitigate solidification cracking [38]. The addition of Ce in the Al matrix narrows down the freezing range. Al-3Ce-7Cu was printed successfully with 0.03% porosity and a UTS of 456 MPa in as printed condition. The alloy showed good tensile strength (UTS:186 MPa, YS:176MPa) at 250°C as well [39].

#### **2.5 Post-processing heat treatment**

High cooling rates inherent to AM process enable the achievement of unique metastable microstructures in the as-fabricated parts, which are readily transformed to equilibrium phases upon exposure to high temperatures. It is a common practice in industries to carry out a stress-relieving heat treatment to dimmish the risk of distortion or cracking due to high residual stresses after rapid thermal cycling of AM processes like L-PBF. Although in most cases, a simple heat treatment cycle serves for the intended application of AM products, some demanding applications may require a combination of this heat treatment with hot isostatic pressing.

As a general observation in the case of AM aluminum alloys, the conventional heat treatment procedures applicable for cast/wrought aluminum alloys involving solution heat treatment and ageing destroy the strengthening benefits gained through L-PBF, whereas a direct aging treatment can retain some of these benefits and still sufficiently relieves the residual stresses [40].

A typical problem faced by precipitation strengthened (e.g., Al 2xxx) aluminum alloys is posed by their low ageing temperature. While these alloys are age-hardened for strengthening between 150 and 200°C, this temperature is not high enough to relieve the residual stresses in the L-PBF parts, which need a temperature around 300° C. If stress relief is carried out at 300°C, strength in these alloys may only be regained by solution treatment followed by precipitation hardening. However, solution treatment of L-PBF precipitation hardenable alloys eradicates the beneficial effects of rapid solidification gained by rapid laser processing. Hence, it is difficult to use typical heat-treatable aluminum alloy for laser processing and gain its advantage originally inherent to artificially aged wrought aluminum alloys.

Alternatively, an alloy that can be age-hardened (or retain the strength gained during AM) at a stress-relieving temperature of 300°C may serve as a HSAA. Such an alloy can retain the gained strength while still relieving the residual stresses with a single aging treatment (direct aging). The addition of a slow diffusion element (like Sc/Zr) to conventionally non-heat treatable Al-alloys of 3xxx and 5xxx series has induced remarkable strengthening since they tend to age-harden at much higher temperatures (≥300°C) (see **Table 2**).

**Figure 5** presents the alloying element(s)-wise tensile yield strength (YS) and elongation% of some selected HSAAs from the research literature. It can be observed


*\* P—power (watts), SS—scan speed (mm/s), t—layer thickness (mm), HS—hatch spacing (μm). D-Ageing—Direct aging, St + aged—solution treated and artificially aged.*

### **Table 2.**

*Mechanical properties and process parameters of Sc, Zr alloyed HSAAs.*

#### **Figure 5.**

*Alloying element-wise tensile yield strength and elongation of selected high-strength alloys [11, 14, 38, 41–57]. TE—transition element(s), AB—as-built, SA—solution treated and aged, DA—Direct aged.*

that many of these alloys demonstrate a YS higher than 350 MPa (comparable with that of conventional wrought HSAAs).

It can be inferred from **Figure 5** that a yield strength superior to 550 MPa and reasonable ductility can be achieved in Al-Mn-transition element(s) alloy after direct aging heat treatment. Without alloying of transition elements, a yield strength superior to 450 MPa has been achieved with close to 10% elongation in L-PBF using Al-Zn + Ti, B and Al-Cu + CaB6 (composite ball-milled powders.

## **3. Directed energy deposition of aluminum alloys**

Directed energy deposition (DED) is defined as a process in which focused thermal (laser, electron, or plasma) energy melts the feedstock material during deposition. Argon or nitrogen gas is used as a shielding gas to protect against the formation of aluminum oxide scale during thermal exposure. The most widely applied DED processes are wire arc additive manufacturing (WAAM) and laser DED (or Laserengineered net shaping) processes.

Several studies investigated the deposition of aluminum alloys by laser-directed energy deposition (DED) [58, 59]. However, the results are not much promising, and several challenges lie ahead of DED of aluminum alloys to compete with conventional wrought alloys or their additively manufactured L-PBF counterparts.

DED of high-strength aluminum alloys faces technical challenges due to the high surface reflectivity of Aluminum, and higher laser power input is required to melt the blown aluminum powder completely [60]. This in turn leads to gas porosity by selective evaporation of lighter constituent elements such as Magnesium and Zinc [58, 61]. The high coefficient of thermal expansion (CTE) of aluminum alloys leads to shrinkage upon solidification followed by cracking or severe deformation due to intense repetitive thermal cycling during the DED process [62]. The inherent tendency of surface oxidation and moisture absorption from the atmosphere [62, 63] and poor flowability of powder, owing to low density, adversely affects the powder mass flow rate, which results in inferior quality of deposit [64].

In more recent studies on DED of high-strength Al-7075 alloy using gas-atomized powders, a crack-free, low-defect bulk material was deposited having an ultimate tensile strength of 222 17 MPa and an elongation of 2%, which is significantly lower than the wrought 7075-T6 [65]. Moreover, the hardness only increased from (85 4) HV0.5 to (93 2) HV0.5 upon artificial aging. In another study on DED of Al-7050 alloy, hardness of a 100HV was achieved in an as-built, defect-free bulk deposit; subsequent heat treatment increased the hardness to 128 HV [61]. Due to the relative ease of deposition and wide processing window Al-Si alloys have results comparable with those of cast counterparts; however, as of now, high-strength aluminum alloys could not be deposited successfully with DED.

## **4. Particulate-reinforced aluminum-based composites**

Aluminum matrix composites (AMCs) have already found wide applications in the aerospace and automotive industries. AM of AMCs gained particular interest due to freedom of design possibilities and further opportunities for weight reduction through modification of properties by reinforcement of Al-matrix. Either an *ex situ* or *in situ* approach is utilized for the optimization of microstructure and the resulting

properties in AM. In "*ex situ*" AMCs, the reinforcements are synthesized externally and then added to the matrix, while the reinforcements are synthesized during AM process in the "*in situ*" AMCs. While *ex situ* AMCs synthesized using L-PBF have shown promising results, the limitations such as poor wettability of reinforcement by the Al-matrix, limited ability of grain refinement, and a higher likelihood of residual stress due to difference in thermophysical properties between the reinforcement and the matrix cannot be overruled [66].

Various methods are adopted for mixing powders of metallic alloys (matrix) and reinforcements. The selected method affects the resultant powder morphology and influences the laser reflectivity and the heat transfer process during L-PBF. A list of the selected methods and the factors to consider before choosing a particular process over the others is presented in **Table 3**.

Though the direct mixing process is simple, agglomeration of fine particles (nanosized) and poor wettability are inevitable.

Ball milling is much popular due to its low cost and wide applicability to several powders. Being a nonequilibrium process, it includes a repetitive sequence of deformation, fracture, and cold welding of metal powder particles [67]. Initially, fracture occurs in brittle reinforcement particles, while cold welding dominates in the Almatrix powder due to plastic deformation. During this deformation and cold welding, reinforcement powders are dispersed in the matrix. Since the Al-matrix gets harder following deformation and cold welding, once again fracture phase dominates until certain dynamics between cold welding and fracture ensures a stable powder size


#### **Table 3.**

*Methods for preparation of feedstock for L-PBF.*

## *Additively Manufactured High-Strength Aluminum Alloys: A Review DOI: http://dx.doi.org/10.5772/intechopen.109697*

without agglomeration [68]. Ball milling induces grain refinement in the milled powders, mainly due to high energy input accompanied by severe plastic deformation into the powders. The process includes the generation of various crystal defects (dislocations, point defects), which increase the internal energy of the system(lattice) with the subsequent evolution of final grain boundaries, thus relieving the high energy. Ball milling also offers the freedom of choosing a wide size range of powders/granules as the starting material size. However, the irregular shape, rough surface, and flattening of Al-powder adversely affect the flowability of ball-milled Al-powders. Being highly ductile, Al alloys need longer duration milling cycles as compared with steels or titanium alloys. Han et al. [69] milled 4 vol.% Al2O3/Al powders with up to 20 h milling using different milling strategies (presented in **Table 4**).

Hence, a careful selection of a processing route for composite feedstock synthesis/ production and selection of optimum processing parameters is pivotal to achieve desirable properties in AM of HSAAs.

The laser absorptivity of Al-composite powders tends to increase with the addition of reinforcements, and it increases with an increase in the amount of reinforcement in the composite. For example, the laser absorptivity of AlSi10Mg is 0.09 [70], while TiB2/AlSi10Mg composite powder has an absorptivity of 0.71 [71]. Thermal conductivity is another important thermophysical property to consider in the case of Almatrix composites. Independent of their thermal conductivity, nano-sized reinforcement particles tend to decrease the effective thermal conductivity of the composite powders because they introduce interfacial thermal resistance and scatter the energy carriers [72].

In short, there are several considerations for the selection of an appropriate reinforcement, which are interdependent, and hence, the selection of reinforcement needs due attention. Any change in the physical and thermal property of feedstock can lead to redistribution of the thermal field and causes changes in fluid dynamics.

In a recent study, Al-2024, an age-hardenable Al-alloy powder, was modified by mechanical alloying using the ball milling technique. 0.5 w% of CaB6 nanoparticles of 200nm (avg. size) were milled with Al-2024 powder (63 μm) for 2h at 150 rpm, baked for moisture removal, and then printed using the L-PBF technique. A good combination of mechanical properties (UTS: 478 MPa, YS: 428 MPa, el.: 13%),


#### **Table 4.**

*Ball milling parameter of 4 vol.% Al2O3/Al [69].*


*\* P—power (watts) SS—scanning speed (mm/s), LT—layer thickness (μm), HS—Hatch spacing (μm), Spot S—spot size (μm).*

#### **Table 5.**

*Mechanical properties and processing parameters of AMCs.*

comparable with those of conventional wrought Al-2024 was achieved in as-built condition. The CaB6 nanoparticles acted as highly effective heterogeneous nuclei due to low lattice mismatch with Al-matrix and facilitated CET, thus enabling a crack-free build [50].

Extensive research has been conducted to reveal and assess the strengthening mechanisms involved in the strengthening of composites (not discussed in this text), and different strength prediction models have been proposed. A quadratic summation strength prediction model, originally proposed by Clyne and later modified by Sanaty-Zadeh [73], can be used for estimating the strength of nano-composites.

$$
\sigma\_{\mathcal{Y}} = \sigma\_{\mathcal{m}0} + \sqrt{\left(\Delta\sigma\_{\text{Ownau}}\right)^2 + \left(\Delta\sigma\_{\text{GR}}\right)^2 + \left(\Delta\sigma\_{\text{load}}\right)^2 + \left(\Delta\sigma\_{\text{CTE}}\right)^2 + \left(\Delta\sigma\_{\text{Modulus}}\right)^2} \tag{1}
$$

Where *σm*<sup>0</sup> is the yield strength of the unreinforced matrix, Δ*σOrowan* is the contribution by Orowan strengthening, Δ*σGR* is a contribution by grain size strengthening, Δ*σload* is a contribution by load-bearing strengthening, Δ*σCTE* is a contribution by dislocation density strengthening, andΔ*σModulus* is a contribution by elastic modulus mismatch strengthening.

However, there is no consensus as to which model closely reflects reality, up till now. Since all models assume a perfect distribution of particles and bonding of interfaces, the calculated values from these models are always higher than the experimental values nevertheless showing a similar trend.

**Table 5** presents the powder preparation methods, processing technique(s), mechanical properties, and laser processing conditions used for deposition in the most recent publications. These data also give a fair picture of the most recent HSAA composites and well reflect the possibility of modifying the properties (mechanical strength, wear resistance, etc.) of base aluminum alloy by the addition of appropriate reinforcement. The strengthening in such composites has reportedly been gained through multiple strengthening mechanisms, as mentioned earlier.

## **5. Conclusions**


## **Acknowledgements**

This research was funded by FEDER through programs P2020|COMPETE - Projetos em Copromoção (POCI-01-0247-FEDER-039796\_LISBOA-01-0247- FEDER-039796) and P2020|COMPETE - Programas Mobilizadores (POCI-01-0247- FEDER-046100).

*Recent Advancements in Aluminum Alloys*

## **Author details**

Fahad Zafar1,2\*, Ana Reis1,2, Manuel Vieira1,2 and Omid Emadinia<sup>2</sup>

1 Faculty of Engineering, University of Porto, Porto, Portugal

2 LAETA/INEGI–Institute of Science and Innovation in Mechanical and Industrial Engineering, Porto, Portugal

\*Address all correspondence to: up202103288@edu.fe.up.pt

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Additively Manufactured High-Strength Aluminum Alloys: A Review DOI: http://dx.doi.org/10.5772/intechopen.109697*

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## Section 3
