Influence of Al{sub}2O{sub}3 particulate on the aging response of A356 Al-based composites

摘要

A356 Al alloy reinforced with Al{sub}2O{sub}3 particulates of different sizes (25 μm angular or 40 μm microsphere) and volume fractions (5, 10 and 20 vol.%) was prepared using vortex method. The influence of Al{sub}2O{sub}3 particulates on the precipitation and hardening behavior of the A356 Al-Al{sub}2O{sub}3 composites was studied. It was found that the MgAl{sub}2O{sub}4 spinel formed at the interface led to Mg depletion in the matrix and subsequently to lesser age hardening in the composites. Therefore, it was necessary for the composite matrix to have a higher Mg concentration prior to casting to achieve the same level of hardening in the composite as in the unreinforced. Different amounts of Mg, depending upon the volume fraction of the Al{sub}2O{sub}3 particulates, were added into the composite melts. The results showed that the hardening kinetics was enhanced by Al{sub}2O{sub}3 particulate additions because hardening precipitates preferentially developed on the dislocation lines that increased due to coefficient of thermal expansion mismatch between the matrix and reinforcement. However, the presence of reinforcement did not alter precipitation sequence of the investigated composites.