Microstructure and Abrasive Wear Studies of Laser Clad Al-Si/SiC Composite Coatings

Surface coatings of Al-Si/SiC metal-matrix composites were deposited on Al-7 wt. % Si alloy substrates by laser cladding. The microstructure of the coatings was characterized by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The microstructure of the coating material is profoundly influenced by the processing parameters used, in particular by the particle injection velocity and by the specific energy. When the injection velocity is low or specific energy is high excessive dissolution of SiC in the melt pool occurs. The microstructure of the coatings presents partially dissolved SiC particles, and considerable proportions of Al4SiC4 plates and faceted Si equiaxed crystals dispersed in a α-Al+Si eutectic matrix. On the contrary for high injection velocity or low specific energy dissolution of SiC is very limited and the microstructure of the coatings consists essentially of undissolved SiC particles in a matrix consisting of primary α-Al dendrites and α-Al+Si eutectic. Abrasive wear tests were performed on the coatings using a ball cratering device and a 35 wt. % suspension of 4.25 μm average diameter SiC particles in water as abrasive. Coatings prepared with a high specific energy present an average hardness of 248 HV and an average abrasive wear rate of 17.4x10-5 mm3/m. Coatings deposited with a low specific energy exhibit an average hardness of 117 HV and an average abrasive wear rate of 4.3 x10-5 mm3/m.