High Temperature Deformation of SiC Whisker/ AZ91 Magnesium Alloy and SiC Whisker/2324 Aluminum Alloy Composites

Both cast and extruded composites of SiC whisker reinforced AZ91 magensium and 2324 aluminum alloys were fabricated by high pressure infiltration of the alloy melt and hot extrusion of the composite ingot. Deformation behavior at elevated temperatures was investigated by tensil tests under various conditions. The extruded composites of SiCW/AZ91 and SiCW/2324 showed higher tensile strength than each matrix alloy at temperatures below 573 K. On the contrary, tensile strength of the extruded composites was lower than that of each matrix alloy at temperatures above 573 K. The cast composites of SiCW/AZ91 showed, however, higher tensile strength than the matrix alloy at all the tested temperatures. The strain rate exponent (m-value) of the cast composites was lower than that of the matrix alloy, whereas the m-value of extruded composites was higher than that of the matrix alloy. The highest tensile elongation of SiCW/AZ91 extruded composites was about 100% at 703 K under an initial strain rate of 5×10−2s−1. Lower tensile strength, higher elongation and higher m-value of extruded composites were attributed to their very fine grain structures in which grain boundary sliding preferentially occurred at elevated temperatures.