Spray forming of Al/SiC metal matrix composites

This paper describes the as-sprayed microstructure of a model Al-4wt%Cu/SiC particulate (Al4Cu/SiC_p) metal matrix composite (MMC) manufactured by spray forming, and the relationship between microstructure and solidification conditions during manufacture. Injection of SiC_p into the melt atomization region during the spray forming of Al4Cu results in significant SiC_p incorporation into molten droplets during atomization, and relatively little incorporation during flight to the substrate and at deposition. SiC_p clustering is evident in the Al4Cu droplets and results in clustering in the as-sprayed MMC deposit. Matrix dislocation and precipitation microstructures are dependent upon local solidification conditions during spray forming. Increased dislocation density and increased quantity of fine-scale θ′-Al₂Cu precipitation is found in the α-Al(Cu) matrix where local deposit cooling rates are high, i.e. in the vicinity of the substrate/deposit interface and when increased spray distances are used in manufacture. Lower dislocation density and increased quantity of grain-boundary θ-Al₂Cu is found where deposit cooling rates are relatively low, i.e. distant from the substrate/deposit interface and at decreased spray distances. In all cases, dislocation densities are higher in α-Al(Cu)/SiC_p interfacial regions than in the α-Al(Cu) matrix. There is no evidence of α-Al(Cu)/SiC_p interfacial reaction in the as-sprayed condition indicating that cooling rates during spray forming are sufficiently rapid to prevent reaction.