Effects of laser remelting process on the microstructure, roughness and microhardness of in-situ cold sprayed hypoeutectic Al-Si coating

In this paper, Al-6 vol.% Si coating was in-situ manufactured by cold spraying from powder mixture of pure Si powder in fraction 25 vol.% with a pure gas-atomized Al powder, mean particle sizes being of 16 μm and 41 μm respectively. Nitrogen was chosen as the spraying and carrier gas to avoid oxidation. The image analysis results show that the Si content in the deposits (6 vol.%) is much lower than that in the feedstock powder (25 vol.%). Due to the high roughness and low bond strength between the Al matrix and the Si particles, a laser remelting process was used to improve these shortages. Results show that the remelted surface layer presents a fine microstructure and a high microhardness. X-ray diffraction analysis indicates that the Al peaks move to the right side (large lattice parameter) after laser remelting process. It could be attributed to two factors: (1) formation of supersaturated Al (Si); (2) large tensile residual stress, due to the high cooling rate. In addition, the laser remelted samples exhibit a lower surface roughness than the corresponding as-sprayed samples.