Study on laser surface remelting of plasma-sprayed Al–Si/1 wt% nano-Si3N4 coating on AZ31B magnesium alloy

Plasma sprayed micro-structured Al–Si based and 1 wt% nano-structured Si3N4 coating was successfully fabricated on an AZ31B magnesium alloy using a high efficiency supersonic atmosphere plasma spraying system, and then the as-sprayed coating was remelted by a continuous wave CO2 laser. The remelted coating was investigated by optical microscope, scanning electron microscope, energy-dispersive spectroscopy, X-ray diffractometer and Vickers microhardness tester. The results indicated that the laser remelted coating possessed an excellent metallurgical bonding to the substrate. A finer dendritic structure was exhibited after laser remelting. The nano-Si3N4 decomposed fully in the coating, and the remelted coating was mainly composed of Al, AlN, Al9Si, Al3.21Si0.47 and Mg2Si. Moreover, the microhardness of remelted coating was enhanced to 200–514HV0.05, which was much higher than that of the substrate(about 50 HV0.05).