**Abstract**

Magnesium can be replaced with materials which experience strain controlled fatigue in their respective applications. Still, there are infrequent predicaments with utilizing magnesium alloys, comprising lower strength, fatigue life, ductility, toughness, and creep resistant attributes correlate with aluminum alloys. Some recent studies have been affirming that through the severe plastic deformation process, particularly equal-channel angular pressing (ECAP) method promotes very significant ultra-grain refinement in bulk solids, which enhances the mechanical properties. ECAP with a 90° clockwise rotation around the billet axis between consecutive passes in route BC has improved the ductile characteristics with increased yield strength and rate of elongation which leads to a greater fatigue life because ultra-fine grain refinement can be able to resist the crack propagations. To attain the plasticity at higher temperature magnesium and its alloys are required to undergo extrusion operation before proceeding to the multiple pass ECAP at 200°C because the magnesium alloys exhibit a limited number of slip systems due to its hexagonal crystal structure.

**Keywords:** magnesium, severe plastic deformation, ECAP, ultra-fine grains, texture

### **1. Introduction**

In today's engineering world, light-weight materials have gained much attention because of demand in low-cost production and increasing efficiency through weight reduction. Correspondingly, Magnesium is one of the materials which attributed in the lightweight material category after aluminum and its alloys. Magnesium and its alloys have some unique application in aerospace and other engineering sectors. But due to some characteristics regarding the manufacturing process such as complex in forming the components and other cold working processes [1]. Particularly in Biomedical application, magnesium has some restriction since Mg dissolves in the body fluid during the restorative process, so degradation of magnesium has to be controlled [2]. One is the low mechanical properties comparing with the bioinert titanium alloys, which makes their application limited in load-bearing implants. Another one is the fast degradation behavior, which involves the gas cavity and high alkaline microenvironment around the implants leading to a poor osteointegration. The mechanical processing of magnesium alloy at elevated temperature influences the grain distribution.

Normally a combination of fine grain structure and coarse grain structure are formed through the various forming operation of wrought materials, and homogeneous grain structures obtained by the cast formed materials [3]. During cold working, the fine grain formed along with the boundaries in the magnesium wrought materials which through the dynamic recrystallization and the distribution is multi-modal [4]. Normally area of the cross section has been reduced through the total plastic deformation method at certain temperature range. Consequently, the methods mentioned above are not having enough capacity to form homogeneous grain refinement at the initial structure and make the grain structure distribution the multimodal phase [5].

For the last few years, the development of plastic deformation technology, which includes the equal channel angular pressing (ECAP) is emerging [6]. The limitation in the plastic deformation of magnesium alloys will neglect through the SPD technique, so severe plastic deformation of magnesium and its alloys initiate the probability for manufacturing the ultrafine grain materials along with the increased mechanical properties and additionally the superplastic capabilities also experienced by the formed material [7].

Towards the application, ECAP paved a path for refinement of grains in the lightweight materials, particularly in concern aluminum and magnesium alloys. In concern with f.c.c metals, misorientation in the low angles boundaries and alignment of the elongated subgrains in parallel to the primary slip will occur when the sample subjected to severe plastic deformation [8, 9]. Followed by the first pass, the upcoming passes designed to induce further refinement of grains and rearrangement consistent with the dislocation theory for low energy structure [10, 11] after the multiple passes in the ECAP, a set of equiaxial grains which in different angles. The structure changes have been accounted in many metals having f.c.c arrangement, which also constitutes aluminum [12]. On the contrary, by using the ECAP process, UFG can be obtained from the magnesium alloys, and grains get refined by the subsequent passes [13].

During the ECAP process of the magnesium and its alloys, grain refinement depends on the number of passes, channel angle, die angle, and the initial grain structure before to the ECAP. By varying the various parameters of the ECAP process, including the temperature, Mg will exhibit diverse morphology such as grain orientation, distribution, size in multimodal type after SPD [12, 13]. Many studies focused on analyzing the microstructure and the mechanical properties after ECAP processing.

As explained, the pattern specified for the grain refinement channels towards a usual perception of the several articles resembling in the research literature and lead to understanding the ability for the further structure of grain formed under the various condition during SPD of magnesium alloys. In magnesium alloys, grain refinement defined in a simple way [14]. This statement is crucial for highlighting, though, that exact grain refinement mechanism elaborated which authorizes various structure formations based on the experimental circumstances including those primary inferences towards maximum processing steps in SPD of magnesium alloys. Different methods regarding severe plastic deformation consistently engage in developing the process and regarding the nanostructure formation in the samples [15].

Under the certain experimental circumstance getting the ultrafine-grained structure along with predominating boundaries oriented in the high degree of angle and it will be varied according to materials. Furthermore, the nanostructure formation in the alloy during the ECAP process is stable in the entire uni, which required for providing durable characteristics for the metals [7, 13]. Followed by, ensuring the ECAP processed samples for mechanical damages or any penetrated cracks in the material. The other methods of SPD will not meet the requirements as above, such as drawing, hot extrusion, and rolling. Nanostructure formation in the samples is only possible with the mechanical deformations at relatively low temperature as well as optimal parameters for material processing [16].

**33**

Mg (pure)

Mg (pure)

Mg (pure)

Mg– 0.9% Al

**Table 1.**

*Severely Plastic Deformed Magnesium Based Alloys DOI: http://dx.doi.org/10.5772/intechopen.88778*

**in Mg and magnesium alloys**

**Alloy Initial** 

**grain size (μm)**

**Final grain size (μm)**

**2. An examination of reports of microstructures produced** 

magnesium and magnesium alloys, which processed through ECAP.

**Intermediate structure**

AZ31 5–30 1.9 A B Pre-deformed by

AZ31 20 1–2 — B Pre-deformed by

AZ31 10 3.2 — B Pre-deformed by

AZ31 28 8 A — One pass of

AZ61 16 0.62 B B Pre-deformed by

AZ91 0.5 — B Pre-deformed by

*Comparison of experiments conducted on pure magnesium and a range of magnesium alloy.*

To make a competent design, it is essential to analyze different grain structures of magnesium and its alloys, which processed through the ECAP [17]. An initial documented reports organized, and general review presented in **Table 1** for pure

The outcome in the given **Table 1** indicates the utilization of an ECAP die set up with the 90 internal channel angle, operating with and without back pressure, and the expected outcomes notified in the column number six of **Table 1**. From the table, A and B represent the heterogeneous and homogeneous grain structure,

AZ31 48.3 2.5 A B \_ [18] AZ31 48.1 1.4 B B U = 100 L [19] AZ31 2.5 0.7 — B U = 110 L [20] AZ31 15–22 1 A B BP-ECAP (423 K) [21]

AZ31 5–30 2.2 A B U = 110 L [23] AZ31 450 1–3 A A [24]

AZ31 10–20 3.0 A B [26]

AZ31 7–20 2 A B Route A [28] AZ31 15–22 0.9 A B BP-ECAP [29]

AZ91 40 1.2 A B Route C [33]

400 120 — B — [34]

200 20 A A — [35]

900 70 A B — [36]

100 17 — B — [34]

**Structure after multiple passes**

**Additional information**

extrusion

hot-rolling

rolling

BP-ECAP

extrusion

extrusion

**References**

[22]

[25]

[27]

[30]

[31]

[32]

*Magnesium - The Wonder Element for Engineering/Biomedical Applications*

the multimodal phase [5].

enced by the formed material [7].

the subsequent passes [13].

processing.

cold working, the fine grain formed along with the boundaries in the magnesium wrought materials which through the dynamic recrystallization and the distribution is multi-modal [4]. Normally area of the cross section has been reduced through the total plastic deformation method at certain temperature range. Consequently, the methods mentioned above are not having enough capacity to form homogeneous grain refinement at the initial structure and make the grain structure distribution

For the last few years, the development of plastic deformation technology, which

includes the equal channel angular pressing (ECAP) is emerging [6]. The limitation in the plastic deformation of magnesium alloys will neglect through the SPD technique, so severe plastic deformation of magnesium and its alloys initiate the probability for manufacturing the ultrafine grain materials along with the increased mechanical properties and additionally the superplastic capabilities also experi-

Towards the application, ECAP paved a path for refinement of grains in the lightweight materials, particularly in concern aluminum and magnesium alloys. In concern with f.c.c metals, misorientation in the low angles boundaries and alignment of the elongated subgrains in parallel to the primary slip will occur when the sample subjected to severe plastic deformation [8, 9]. Followed by the first pass, the upcoming passes designed to induce further refinement of grains and rearrangement consistent with the dislocation theory for low energy structure [10, 11] after the multiple passes in the ECAP, a set of equiaxial grains which in different angles. The structure changes have been accounted in many metals having f.c.c arrangement, which also constitutes aluminum [12]. On the contrary, by using the ECAP process, UFG can be obtained from the magnesium alloys, and grains get refined by

During the ECAP process of the magnesium and its alloys, grain refinement depends on the number of passes, channel angle, die angle, and the initial grain structure before to the ECAP. By varying the various parameters of the ECAP process, including the temperature, Mg will exhibit diverse morphology such as grain orientation, distribution, size in multimodal type after SPD [12, 13]. Many studies focused on analyzing the microstructure and the mechanical properties after ECAP

As explained, the pattern specified for the grain refinement channels towards a usual perception of the several articles resembling in the research literature and lead to understanding the ability for the further structure of grain formed under the various condition during SPD of magnesium alloys. In magnesium alloys, grain refinement defined in a simple way [14]. This statement is crucial for highlighting, though, that exact grain refinement mechanism elaborated which authorizes various structure formations based on the experimental circumstances including those primary inferences towards maximum processing steps in SPD of magnesium alloys. Different methods regarding severe plastic deformation consistently engage in developing the process and regarding the nanostructure formation in the samples [15]. Under the certain experimental circumstance getting the ultrafine-grained structure along with predominating boundaries oriented in the high degree of angle and it will be varied according to materials. Furthermore, the nanostructure formation in the alloy during the ECAP process is stable in the entire uni, which required for providing durable characteristics for the metals [7, 13]. Followed by, ensuring the ECAP processed samples for mechanical damages or any penetrated cracks in the material. The other methods of SPD will not meet the requirements as above, such as drawing, hot extrusion, and rolling. Nanostructure formation in the samples is only possible with the mechanical deformations at relatively low temperature as

well as optimal parameters for material processing [16].

**32**
