*2.2.1 Extrusion*

The MMNC billet is stressed under high pressure ram inside a die which quantitatively reduces the irregularities like pores, cavity, voids and cracks formed earlier in primary processing methods. Normally carried above recrystallization temperature, the hot extrusion processes can be categorized into;


The difference in the two method is the flow of billet direction. The billet extruded on the direction of the ram is direct extrusion while in the backward extrusion, the billet is extruded opposite to the direction of movement of ram. Typical forward extrusion process in shown in **Figure 10**. The key process parameters are extrusion ratio, temperature during extrusion and the speed of the ram. Extrusion ratio in the ratio between initial to the final cross section of the billet. The working temperature and environment should be optimally decided to eliminate oxidation during extrusion.

**21**

*2.2.2 Rolling*

**Figure 10.**

the load required for plastic deformation.

*Schematic representation of direct extrusion process.*

*2.2.3 Equal channel angular pressing (ECAP)*

shear strain for the individual passes can be obtained by:

γ = 2 *cot*(

Rolling is a plastic deformation process in which the MMNCs are deformed by passing through set of high-pressure rolls. The MMNCs are deformed plastically by compressive stress and squeezing action between the rolls. The process enables the MMNCs to obtain fine grain microstructure and eliminates defects caused in the primary processing. The benefits include fine grain microstructure and enhanced mechanical properties of the material. The process parameters are percentage reduction, temperature and the number of passes to achieve the final thickness on the MMNCs. Rolling is also normally carried out a higher temperature to minimize

ECAP (**Figure 11**) is used to form ultrafine-grained (UFG) microstructure MMNCs. The MMNC billet is passed through two channeled die with identical cross section that intersect at an angle Φ (channel intersection angle). During the process the billet undergoes severe plastic shear deformation (SPD) without altering the geometrical cross-section. The process is normally repeated for several passes in order to attain UFG structure. Different routes followed namely A, BA, BC and C as discussed elsewhere [71]. Previous researcher [71] reported that when Φ is 90°, enhanced grain refinement is realized due to increase in the shear strain (γ). The

> \_\_ Φ

In an earlier research [16] conducted on Mg-9Al-1Si-1SiCn composite, ECAP was performed at a temperature of 360 °C. Route BC was chosen with

<sup>2</sup> ) (3)

*Synthesis of Magnesium Based Nano-composites DOI: http://dx.doi.org/10.5772/intechopen.84189* *Synthesis of Magnesium Based Nano-composites DOI: http://dx.doi.org/10.5772/intechopen.84189*

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

and diameter of 6 mm. The pin less tool was fed first to prevent the nano-phase getting distorted from the groove. The second tool with pin was then passed to complete the process. The tool rotation (800–1400 rpm) and the traverse speed (45 mm/min) were varied to obtain the desired strength and structure of the composite. Higher hardness was observed due to grain refinement at higher tool

Secondary processing is essentially performed on primary processed composites to eliminate/minimize defects and microstructural irregularities to enhance mechanical properties such as strength, hardness etc. Secondary processing methods include bulk deformation process such as extrusion/rolling/friction stir processing and severe plastic deformation processing methods such as equal channel

The MMNC billet is stressed under high pressure ram inside a die which quantitatively reduces the irregularities like pores, cavity, voids and cracks formed earlier in primary processing methods. Normally carried above recrystallization tempera-

The difference in the two method is the flow of billet direction. The billet extruded on the direction of the ram is direct extrusion while in the backward extrusion, the billet is extruded opposite to the direction of movement of ram. Typical forward extrusion process in shown in **Figure 10**. The key process parameters are extrusion ratio, temperature during extrusion and the speed of the ram. Extrusion ratio in the ratio between initial to the final cross section of the billet. The working temperature and environment should be optimally decided to eliminate

angular pressing (ECAP) and cyclic extrusion and compression (CEC).

ture, the hot extrusion processes can be categorized into;

**20**

rotational speed.

**Figure 9.**

*2.2.1 Extrusion*

**2.2 Secondary processing methods**

*FSP fabrication stages from 1 to 3 for Mg nano-composite [67].*

1.Forward or direct extrusion

oxidation during extrusion.

2.Backward or indirect extrusion

**Figure 10.** *Schematic representation of direct extrusion process.*

### *2.2.2 Rolling*

Rolling is a plastic deformation process in which the MMNCs are deformed by passing through set of high-pressure rolls. The MMNCs are deformed plastically by compressive stress and squeezing action between the rolls. The process enables the MMNCs to obtain fine grain microstructure and eliminates defects caused in the primary processing. The benefits include fine grain microstructure and enhanced mechanical properties of the material. The process parameters are percentage reduction, temperature and the number of passes to achieve the final thickness on the MMNCs. Rolling is also normally carried out a higher temperature to minimize the load required for plastic deformation.

#### *2.2.3 Equal channel angular pressing (ECAP)*

ECAP (**Figure 11**) is used to form ultrafine-grained (UFG) microstructure MMNCs. The MMNC billet is passed through two channeled die with identical cross section that intersect at an angle Φ (channel intersection angle). During the process the billet undergoes severe plastic shear deformation (SPD) without altering the geometrical cross-section. The process is normally repeated for several passes in order to attain UFG structure. Different routes followed namely A, BA, BC and C as discussed elsewhere [71]. Previous researcher [71] reported that when Φ is 90°, enhanced grain refinement is realized due to increase in the shear strain (γ). The shear strain for the individual passes can be obtained by:

$$\gamma = 2 \cot \left( \frac{\Phi}{2} \right) \tag{3}$$

In an earlier research [16] conducted on Mg-9Al-1Si-1SiCn composite, ECAP was performed at a temperature of 360 °C. Route BC was chosen with

**Figure 11.** *Schematic diagram of four ECAP routes [71].*

ram speed of 2 mm/min. Homogenization heat treatment was carried prior to ECAP. Homogenized ECAP composite billet exhibited superior ductility and tensile strength.
