Effect of cooling rate on microstructure and properties of SiCP/A359 composites

Abstract

The microstructure and properties of stirred cast SiCP/A359 composites under different cooling rates were studied. The strengthening mechanism of the composite material under three cooling rates was analyzed, and the failure mechanism of the composite material was elucidated by means of in-situ tension and EBSD testing. The results showed that increasing the cooling rate simultaneously refined the grains, secondary dendrites, and eutectic silicon, resulting in improved distribution uniformity of SiC and the stacking fault density of eutectic silicon. Additionally, the relationship between the secondary dendrite arm spacing (SDAS) and cooling rate (v) of the SiCP/A359 composite was described using the equation SDAS = 56.02v^(-0.3). There was a positive correlation between cooling rate and yield strength, with particle strengthening being the main contributor to the strength of composites with high cooling rates, resulting in significantly higher strength than samples with low cooling rates. The geometrically necessary dislocations (GND) density at the eutectic Si-Al boundary was found to be higher than other positions after the material was loaded, and the main crack propagated mainly along the eutectic region. Secondary cracks, including SiC cracking, eutectic silicon cracking, interface separation, and shrinkage cracking, may become part of the main crack by bridging.