High Temperature Mechanical Behavior and Microstructure of α-Si ₃N₄w/4032Al Composite Fabricated by Squeeze Casting

The effect of compressive deformation parameters such as temperature and strain rate on the microstructures and the mechanical behavior of α-Si₃N₄ whisker reinforced 4032 aluminum alloy composite was investigated. The compressive temperatures involve below and above the solidus temperature of the α-Si₃N₄w/ 4032Al composite, which was determined by Differential Scanning Calorimeter (DSC). The results show that the flow stress of the α-α-Si ₃N₄w/4032Al composite are much higher than that of the unreinforced 4032Al alloy at low temperatures, but this difference becomes quite small at higher temperatures. Flow stress of the composites enhances with decreasing compressive temperature and increasing strain rate. Strain softening appears during compressive deformation in all the testing conditions. Microstructure observations by SEM and TEM indicate that the rotation and breakage of the whiskers together with the dynamic recovery of matrix alloy during compressive deformation are responsible for all the mechanical behavior indicated above. In addition, there are interfacial reactions between the matrix alloy and the Si₃N₄ whiskers due to segregation of the alloy elements near the matrix/reinforcement interfaces. The compressive deformation mechanisms of the α-Si₃N₄w/4032Al composite are also discussed preliminarily.