Study on laser surface remelting of plasma-sprayed Al-Si/1wt% nano-Si_3N_4 coating on AZ31B magnesium alloy

摘要

Plasma sprayed micro-structured Al-Si based and 1 wt% nano-structured Si_3N_4 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 CO_2 laser. The remelted coating was investigated by optical microscope, scanning electron microscope, energy-dispersive spec-troscopy, 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-Si_3N_4 decomposed fully in the coating, and the remelted coating was mainly composed of Al, AlN, Al_9Si, Al_(3.21) Si_(0.47) and Mg_2Si. Moreover, the micro-hardness of remelted coating was enhanced to 200-514HV_(0.05). which was much higher than that of the substrate(about 50 HV_(0.05)).