Effects of casting temperature on the microstructure and wear resistance of compocast A356/SiCp composites:: a comparison between SS and SL routes

In the present study, aluminium A356 alloy was reinforced with SiC particles using compocasting techniques and the effects of casting temperature on the composite properties were investigated. Different volume fractions of SiC particles of various sizes were incorporated into the semisolid alloy by a mechanical stirrer. Then the slurry was poured into a permanent die of certain dimensions pre-heated to various temperatures either when the metal alloy was partially solid (semisolid-semisolid or SS route) or after reheating to above the liquidus temperature of the alloy (semisolid-liquid or SL route). Microstructural characterisation studies conducted on the SL samples revealed a more uniform distribution of SiC particulates (at the microscopic scale) and less porosity content when compared to the SS samples, regardless of the mould pre-heat temperature or the size and content of the SiC particles. However, the observed settling of the SiC particles (when the slurry was poured into a tall and pre-heated mould) was less pronounced. Results of pin on ring wear test demonstrated an increase in wear resistance in the case of the SS samples when compared to SL and matrix alloy samples. These observations were finally rationalised in terms of the casting temperature, which resulted in the variations of the microstructural characteristics and formation of globular or dendritic microstructures for the SS and SL samples respectively. (C) 2004 Elsevier B.V. All rights reserved.