Effects of magnesium on wear characteristics of SiC and AI203 reinforced aluminum metal matrix composites

Abstract

The aim of this work is to investigate the effects of magnesium (Mg) on wear characteristics of silicon carbide (SiC) and alumina (Al2O3) reinforced aluminum metal matrix composites (Al-MMC). Al-MMC reinforced with varying wt. % of SiC and Al2O3 particles were fabricated using stir casting fabrication technique. Effects of Mg, heat treatment and amount of reinforcements on microstructure, tensile strength, hardness and wear characteristics of Al-MMC were investigated. Worn surfaces were also studied to reveal the mechanism involved in wear process. Microstructural observation revealed random dispersion of reinforcing particles in Al matrix. Cluster of particles and porosities were observed in the microstructure. Many regions in the matrix were also observed without reinforcing particles indicating non-homogeneous distribution of reinforcing particles. In SEM observation, agglomerated particles, good adhesion between reinforcing particle and Al matrix and precipitation caused by heat treatment were observed. SiC reinforced Al-MMC showed superior tensile strength than unreinforced Al and increased with increasing SiC content. Non-homogeneous distribution of reinforcement adversely affected tensile strength of Al-MMC. Mg addition was found to be beneficial for hardness of both unreinforced Al and Al-MMC. Further increase of hardness occurred after heat treatment. Hardness values of Al-MMC was found higher than those of unreinforced Al and increased with increasing amount of SiC particles. SiC Particles reinforced Al-MMC showed lower wear rate than unreinforced Al and wear rate decreased with increasing amount of SiC particles. Mg addition reduced the wear rate of both unreinforced Al and Al-MMC. Al-MMC containing higher amount of SiC than Al2O3 showed better wear resistance due to higher hardness value of SiC particles and wear rate decreased after heat treatment. From worn surfaces observation it was seemed that delamination wear mechanism was involved in wear process of Al-MMC where severe fracture and plastic deformation occurred.