Aluminium and Its Interlinking Properties

K. Velmanirajan and K. Anuradha

## Abstract

Aluminium and its alloys are preferred materials, because of its varied desirable properties, availability and inexpensiveness. Aluminium alloys exist in several different grades available in the market commercially, from pure (about 99% Al content) to specific varieties based on the impurities contained in it by chemical composition. The properties are differing in nature which can be scientifically seen and justified in different perspectives. The properties such as forming, fracture mode, tensile, etc. can be seen through the metallurgical aspect, chemical aspect, crystallographic texture, forming limits and mechanical properties. The truth of its properties can be viewed by interlinking/correlating nature of its different studies. The purpose of this chapter is to show the correlating nature of different properties of aluminium of same and different grades.

Keywords: crystallographic texture, annealing, tensile, formability, void

### 1. Introduction

Ease of possessing light weight, formability and good strength-to-weight ratio are the desirable properties opted by the designer in the selection of materials for most modern engineering applications. Aluminium alloys vary by their tensile properties, formability properties and surface characteristics from one another at different dimensions, annealing temperatures, duration of annealing and mode of cooling, composition and percentage of initial strain [30–35]. In sheet metal forming, force is applied to a piece of sheet metal to modify its geometry rather then to remove any material. The applied force and stress on the sheet metal beyond its yield strength causes the material to plastically deform, without failing. As a result, the sheet can be bent or stretched into a variety of complex and required shapes. The forming operations of sheet metal include various types and conditions of strains, which can be significantly evaluated to predict the properties of the metal and its forming limit [2]. Preferably, the forming operation is done in most of the engineering applications, which require annealing procedures, microstructure examination, characterization of the sheets and their relations to attain higher formability [3].

The characterization involves the experimental determination of the microstructural aspects, tensile properties and formability parameters such as average plastic strain ratio and planar anisotropy [4]. For evaluating the forming limit diagrams (FLD), the results from the three strain conditions are combined. The formation of the crystallographic texture on the initial material also influences the formability of the sheet metal. Fracturing occurs in sheet metal forming when the strain exceeds a critical value and is considered as a factor determining the fracture limit diagram. The effect of sheet thickness on formability is a trend in study [5] (Rahavan et al., 2010). It is undertaken to interlink the formability of commercially pure aluminium grades of sheet metal through the study of mechanical (tensile) properties, formability property, forming limit diagrams, void coalescence properties and texture properties by experiments from the established results. Thus the study of the properties by one mode to the other is based on its correlation and interlinking properties.

## 2. Chemical composition

The aluminium alloy of grades, namely, Al 1350, Al 8011 and Al 1145, available in the market in the form of cold-rolled sheets with different thickness of 1.2, 1.5 and 1.8 mm, respectively, with different chemical compositions are chosen for the study.

Fe and Si particles are capable of stabilizing finer grains, which enhance the strength and ductility [13]. The presence of iron increases the recrystallization temperature, and silicon improves the fluidity of the alloy [25]. The addition of copper reduces pitting corrosion [25]. With the least presence of chromium or manganese and iron, aluminium alloy Al 8011 may form FeAl3. The other elements include copper, manganese, magnesium, zinc, chromium, nickel, cadmium, lead and titanium, which are represented in Table 1 and are in negligible amounts.


Table 1.

Chemical composition of commercially pure aluminium alloy sheets of different thicknesses (In wt %) [34, 35].

## 3. Annealing

Figure 1 indicates the duration of annealing (1hr) which was followed by cooling in furnace. These sheet metals were subjected to four different annealing temperature treatments, namely, 200, 250, 300 and 350°C; soaking time was 1 h, and furnace cooling was considered for experimentation and for forming operations.

#### 4. Microstructure

In a microstructural analysis of Al 1350, the result of the microstructural analysis of Al 1350 has been tabulated in Table 2, which has partial recovery and no crystallization at an annealing temperature of 200°C. But at an annealing temperature of 250°C, it has partially recrystallized fully recovered microstructure.

microstructure, similarly at 300°C also. The sheet annealed at 350°C shows fully

Diagram showing plot of annealing time versus annealing temperature: (a) 200°C, (b) 250°C, (c) 300°C and

200 0° 0.122 0.583 166.2 119.2 139.9 14.42

250 0° 0.135 0.56 189.4 112.6 129.9 23.58

300 0° 0.146 0.753 211.3 101.3 116.1 31.10

350 0° 0.167 0.925 290.2 95.6 106.0 45.34

(MPa)

Yield strength (MPa)

Ultimate strength (MPa)

% elongation

Orientation n-value r-value k-value

45° 0.144 0.530 171.1 90° 0.166 0.521 176.5 Average 0.144 0.541 171.2

45° 0.154 0.692 192.1 90° 0.240 0.59 180.8 Average 0.171 0.6335 188.6

45° 0.164 0.602 210.6 90° 0.280 0.724 225.4 Average 0.189 0.670 214.5

45° 0.175 0.853 264.14 90° 0.290 0.771 280.4 Average 0.202 0.851 274.7

Tensile properties of Al 1350 alloy sheets annealed at different temperatures [30, 32–35].

inter metallic phases which appeared as dark areas in the aluminium matrix as shown in Figure 2, and certain second-phase particles were found to be present in

The microstructure of the aluminium alloy containing silicon and iron consists of

recovered and recrystallized microstructure.

Figure 1.

Table 2.

35

(d) 350°C [30, 32–35].

Aluminium and Its Interlinking Properties DOI: http://dx.doi.org/10.5772/intechopen.86553

Annealing temperature (°C)

The 200°C annealed sheet shows partial recovery with no recrystallization. The sheet annealed at 250°C is fully recovered and is partially recrystallized

#### Figure 1.

the formability of the sheet metal. Fracturing occurs in sheet metal forming when the strain exceeds a critical value and is considered as a factor determining the fracture limit diagram. The effect of sheet thickness on formability is a trend in study [5] (Rahavan et al., 2010). It is undertaken to interlink the formability of commercially pure aluminium grades of sheet metal through the study of mechanical (tensile) properties, formability property, forming limit diagrams, void coalescence properties and texture properties by experiments from the established results. Thus the study of the properties by one mode to the other is based on its correlation

The aluminium alloy of grades, namely, Al 1350, Al 8011 and Al 1145, available in the market in the form of cold-rolled sheets with different thickness of 1.2, 1.5 and 1.8 mm, respectively, with different chemical compositions are chosen for the

Fe and Si particles are capable of stabilizing finer grains, which enhance the strength and ductility [13]. The presence of iron increases the recrystallization temperature, and silicon improves the fluidity of the alloy [25]. The addition of copper reduces pitting corrosion [25]. With the least presence of chromium or manganese and iron, aluminium alloy Al 8011 may form FeAl3. The other elements include copper, manganese, magnesium, zinc, chromium, nickel, cadmium, lead and titanium, which are represented in Table 1 and are in negligible amounts.

1.2 mm AA 1350 99.07 0.090 0.139 0.392 0.098 0.010 0.14 0.015 0.019 0.021 1.5 mm AA 8011 98.13 0.919 0.013 0.653 0.096 0.01 0.004 0.026 0.013 0.019 1.8 mm AA 1145 99.4 0.102 0.100 0.254 0.082 0.010 0.003 0.016 0.008 0.025

Chemical composition of commercially pure aluminium alloy sheets of different thicknesses (In wt %) [34, 35].

Figure 1 indicates the duration of annealing (1hr) which was followed by cooling in furnace. These sheet metals were subjected to four different annealing temperature treatments, namely, 200, 250, 300 and 350°C; soaking time was 1 h, and furnace cooling was considered for experimentation and for forming operations.

Si Cu Fe Sn Zn Cr Mn Ni Ti

In a microstructural analysis of Al 1350, the result of the microstructural analysis

The 200°C annealed sheet shows partial recovery with no recrystallization. The

of Al 1350 has been tabulated in Table 2, which has partial recovery and no crystallization at an annealing temperature of 200°C. But at an annealing tempera-

ture of 250°C, it has partially recrystallized fully recovered microstructure.

sheet annealed at 250°C is fully recovered and is partially recrystallized

and interlinking properties.

Aluminium Alloys and Composites

2. Chemical composition

study.

3. Annealing

Table 1.

34

Thickness and grade

Remainder Al

4. Microstructure

Diagram showing plot of annealing time versus annealing temperature: (a) 200°C, (b) 250°C, (c) 300°C and (d) 350°C [30, 32–35].


#### Table 2.

Tensile properties of Al 1350 alloy sheets annealed at different temperatures [30, 32–35].

microstructure, similarly at 300°C also. The sheet annealed at 350°C shows fully recovered and recrystallized microstructure.

The microstructure of the aluminium alloy containing silicon and iron consists of inter metallic phases which appeared as dark areas in the aluminium matrix as shown in Figure 2, and certain second-phase particles were found to be present in

annealed at 200°C (i.e., low temperature) due to the presence of cold-worked microstructure. At annealing temperatures of 250, 300 and 350°C, the ultimate tensile strength and yield stress of metal sheets were found to be low. The percentage elongation, strain hardening index, anisotropy and k-value, however, increased

This may be due to the softening of metal at higher annealing temperatures. Similar behaviour was observed for all grades of aluminium sheets selected. In Al alloy sheet, the factor navrav formability index showed a direct relationship with formability of sheet metal. As the factor navrav increased, the formability also increased [2, 27, 28]. The percentage increase of navrav index in zone 3 was found to be highest due to fully recrystallized microstructure as shown in Figure 4. The next highest was observed in zone 1 (due to full recovery) followed by zone 2. Similar behaviour was observed in all commercially available Al sheets annealed at different

Tables 2 and 3 show the different annealing temperatures of aluminium alloy sheet metals with different mechanical properties and formability properties, namely, strain hardening exponent, yield strength, tensile strength, r-value (plastic

The variation of formability properties with respect to annealing temperatures.

Annealing temperature (°C) Orientation nrav Δr rav 200 0° 0.071126 0.0220 0.541

250 0° 0.09423 0.0025 0.693

45° 0.07632 90° 0.086486 Average 0.077563

45° 0.106568 90° 0.16584 Average 0.118302

with annealing temperature. At 350°C, the annealed sheet showed fully recrystallized microstructure, which may be due to relieving of internal strain energy formed during cold working and formation of new strain-free grains which

increased the percentage elongation.

Aluminium and Its Interlinking Properties DOI: http://dx.doi.org/10.5772/intechopen.86553

temperatures.

Figure 4.

37

Figure 2.

Microstructure of aluminium alloy 1350 sheets annealing at four different temperatures [32, 33].

these alloys. An increase in the annealing temperature shows the presence of a larger amount of precipitated particles; the colour may be grey, which is due to the presence of silicon and white spots [25] is due to the presence of iron, which might ultimately increase the formability. The Fe and Si particles were capable of stabilizing a fine-grain/sub-grain structure, which could be used to develop interesting combinations of strength and ductility [2, 30–35]. Titanium increased the recrystallization temperature, induced grain refinement and remained mostly in solution [26].
