Segregation phenomena of laser alloyed Ni-Cr-Al coating on Al-Si alloy

A plasma sprayed coating (Ni-Cr-Al) on a Al-Si alloy surface was alloyed by a 5 kW CO2 laser. The chemical composition and the microhardness in the laser alloyed zone were examined. It is shown that compositional segregation appears in the laser alloyed zone. A higher Al content is in the surface of the laser melted zone and higher Ni and Cr content are in the inner of the laser alloyed zone. The segregation appears still in the dendrites and interdendritic areas, Ni is rich in the dendrites and both Si and Cr are rich in the interdendritic areas. Some amorphous structures with high microhardness were found in the bottom of the laser alloyed zone, which caused this region to have higher hardness.