Investigations on microstructure, mechanical properties and tribological behavior of in-situ Mg₂Si particles reinforced AZ91 composites

In this work, AZ91 matrix composites reinforced with in-situ Mg₂Si particles were prepared by liquid metallurgy method, and the effect of Mg₂Si phase on the microstructure, mechanical properties and tribological behavior was investigated. The experimental results showed that with the increase of Si concentration, the volume fractions and size of Mg₂Si phase were enhanced gradually, and the morphology of Mg₂Si changed from Chinese script shape to coarse dendritic shape. As the Mg₂Si phase increased, the grain size of composites was refined by 50%, from 215 μm to 108 μm. In addition, both Brinell hardness and yield strength of Mg₂Si/AZ91 composites were improved significantly due to the grain refinement strengthening and load transfer effect. The wear loss of composites was reduced greatly with increasing Mg₂Si phase amount, and as the Mg₂Si addition was 11.5 vol%, it was decreased by 32%, indicating in-situ formed Mg₂Si could significantly improve the wear resistance of AZ91 alloy. Microstructure analysis on worn surface revealed that the composites exhibited smaller value in the width and depth of the grooves, and could resist more plastic deformation and wear damage due to the improved hardness and strength. During the sliding wear process, the wear mechanism of Mg₂Si/AZ91 composites was dominated by abrasive wear, slight plastic deformation and delamination, but it was much less than that of AZ91 alloy.