The Correlation of Microstructure and Mechanical Properties of In-Situ Al-MgSi Cast Composite Processed by Equal Channel Angular Pressing.

In this paper, the effect of equal channel angular pressing (ECAP) on microstructure and mechanical properties of hypereutectic Al-20%MgSi and Al-15%MgSi, as well as hypoeutectic Al-10%MgSi composites has been investigated. After fabricating the composites by in-situ casting, the composites were processed using the ECAP process up to two passes at room temperature. Microstructural studies have been carried out using a field emission scanning electron microscopy equipped with an energy dispersive X-ray spectrometer. Mechanical properties were also documented using Vickers microhardness and shear punch tests. In the hypereutectic composites, a decrease in the average size of pro-eutectic MgSi (MgSi) particles, breakages in eutectic networks, and lengthening of the Al (α) phase in direction of shear bands were observed after the ECAP process. For instance, the average size of MgSi Particles in Al-20%MgSi composite reduced from 40 to 17 μm after 2 passes of ECAP. Furthermore, a uniform distribution of MgSi particles was developed in the matrix. In hypoeutectic composite, the ECAP process caused a uniform distribution of eutectic MgSi (MgSi) in the matrix that considered a favorable microstructure. Microhardness measurements and shear punch results showed an ascending trend after each pass of ECAP for all specimens. For example, microhardness and shear strength of Al-20%MgSi increased from 88 HV and 109 MPa to 119 HV and 249 MPa after two passes indicating 35% and 34% increments, respectively. Density and porosity calculations by Archimedes principle revealed that the density of the composites increased after two passes of ECAP due to the reduction of porosity.