Comparative Study of Electroless Ni-P and Ni-P-SiC on AZ91D Magnesium Alloy

Objective To improve the corrosion resistance and wear resistance of AZ91D magnesium alloy. Methods Ni-P-SiC composite coating and Ni-P coating were directly fabricated by electroless plating using phosphoric acid + ammonium molybdate pickling and HF activation. For comparison,electroless Ni-P coating was prepared at the same time. The morphology,composition,structure,hardness,corrosion resistance and wear resistance of the two coatings were compared systematically. Results The cellular grains of coating were refined by adding SiC powder. SiC phase appeared in the Ni-P-SiC composite coating without changing the basic structure of Ni-P alloy. The hardness of the Ni-P-SiC composite coating reached up to 643HV. The corrosion current density increased slightly in terms of the Ni-P alloy coating. Conclusion Compared with the Ni-P coating,the corrosion resistance of the Ni-P-SiC composite coating declined slightly,but its wear resistance increased greatly.