Fabrication and characterization of Al356/SiCp semisolid composites by injecting SiCp containing composite powders

Al356/5 vol.% SiCp cast composites were fabricated by the injection of reinforcement particles into the melt in three different forms, i.e. as untreated SiCp, milled particulate Al–SiCp composite powder, and milled Al–SiCp–Mg composite powder. The resultant composite slurries were then cast in the semisolid temperature range of the alloy, upon which the effects of the type of injected powder on the distribution and incorporation of the reinforcement particles, along with the hardness of the cast composites, were investigated. Injection of milled composite powders resulted in considerable improvement in SiCp wetting as well as the incorporation and distribution of SiCp in the Al356 matrix alloy. Al356/5 vol.% SiCp composite with well dispersed reinforcement particles of less than 3 μm average diameter was successfully produced by injecting Al–SiCp–Mg composite powder into the melt. The best microstructural characteristics in terms of the reinforcement incorporation and distribution, and the highest hardness value of the cast composites, were achieved when magnesium was added through the injected composite powder and not directly into the melt.