Hot deformation behavior of SiC_w/AZ91 magnesium matrix composite and AZ91 alloy

High temperature compressive deformation of SiC_w/AZ91 composite and unreinforced AZ91 magnesium alloy was performed using Gleeble-1500 thermal simulator in the range of deformation temperature from 423 to 723 K, strain rate from 0.002 to 0.25 s^-1 and maximum deformation strain of 60%. The compressive true stress-true strain curves were measured and hot deformation microstructures were observed. Strain softening behavior of composite is more obvious than that of unreinforced alloy because of the rotation and breakage of whiskers during compression. The strain rate sensitivity exponent (m) and apparent activation energy (Q) of both the SiC_w/AZ91 composite and AZ91 alloy increase with the increasing of temperature. The higher m value of the composite is considered to be resulted from the fine microstructure due to the addition of SiC whiskers. The addition of whisker limits the cross slip of dislocations and migration of grain boundary, which causes Q value of the composite higher than that of the unreinforced alloy. During the compression, dynamic recovery and dynamic recrystallization occur in both the unreinforced alloy and SiC_w/AZ91 composite.