Laser cladding of Al-Si/SiC composite coatings:Microstructure and abrasive wear behavior

Surface coatings of an Al-Si-SiC composite were produced on UNS A03560 cast Al-alloy substrates by laser cladding using a mixture of powders of Al-12 wt.% Si alloy and SiC. The microstructure of the coatings depends considerably on the processing parameters. For a specific energy of 26 MJ/m2 the microstructure consists of SiC particles dispersed in a matrix consisting of primary α-Al dendrites and interdendritic α-Al+Si eutectic. For higher specific energies (58 and 87 MJ/m2) SiC reacts and dissolves partially in molten aluminum, leading to a microstructure consisting of primary Al4SiC4 and Si and a small fraction of undissolved SiC particles dispersed in the matrix. Abrasive wear tests were performed on the coatings using a ball cratering device and a suspension of SiC particles (35 wt.% of SiC with an average particle diameter of 4.25μm) in water as abrasive. The coatings deposited with a low specific energy (26 MJ/m 2) exhibit an abrasive wear rate of 0.43 x10-4 mm 3/m and a hardness of 120 HV, while those prepared with higher specific energy (58 MJ/m2) present a higher wear rate (1.7x10 -4 mm3/m) despite their higher hardness (250 HV). 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. Microploughing and microcutting are the main material removal mechanisms in all samples. Whenever they exist in sufficient proportion, SiC reinforcement particles stop the grooving action of the abrasive, thus decreasing material loss. There is also some evidence of an increased contribution of microcutting as compared to microploughing in samples prepared with high specific energy, an effect that contributes to decrease their wear resistance