Microstructure and wear studies of laser clad Al-Si/SiC(p) composite coatings

Coatings of a composite material consisting of an Al-Si matrix reinforced with SiC particles were produced by laser cladding on UNS A03560 cast Al-alloy substrates from mixtures of powders of Al-12 wt.% Si alloy and SiC. The influence of the processing parameters on the microstructure and abrasive wear resistance of the coatings was studied. For an interaction time of 0.08 s and a power density of 330 MW/m2, corresponding to a specific energy of 26 MJ/m2, the interaction between SiC and liquid Al is limited and the reinforcement particles remain essentially undissolved. The coating's microstructure is formed of SiC particles dispersed in a matrix consisting of primary α-Al dendrites and interdendritic α-Al+Si eutectic. For interaction times of 0.3 and 0.45 s and a power density of 193 MW/m2, corresponding to specific energies of 58 and 87 MJ/m2, SiC reacts with molten Al and partially dissolves. The resulting microstructure consists of undissolved SiC particles, found mainly at the bottom of the clad tracks, where the maximum temperature reached during processing is lower, and Al4SiC4 and Si particles dispersed in a matrix of α-Al+Si eutectic. The coatings prepared with higher specific energy (58 MJ/m2) present a hardness of 250 V and an abrasive wear rate in three-body abrasion tests with SiC as abrasive of 1.7×10−4 mm3/m, while those produced with 26 MJ/m2 present a hardness of 120 V and a wear rate of 0.43×10−4 mm3/m. These results show that Al4SiC4 and Si increase the hardness of the material by dispersion hardening but do not contribute to its abrasive wear resistance, because they are softer than the abrasive particles, and confirm that the parameters used to prepare Al-Si-SiC composite coatings by laser cladding must be selected so that only minimal reactions occur between SiC and molten Al.