Effect of Nd2O3 on microstructure, corrosion and wear properties of laser cladding Zr-based amorphous composite coatings on AZ91D magnesium alloy

The preparation of amorphous matrix composite coatings by laser cladding is a applicable approach to improve the surface properties of Mg and Mg alloys. Rare earth elements significantly affect the corrosion and wear resistance of the coatings by influencing the quantity, morphology and distribution of crystalline phases. In the presented work, Zr55Cu30Al10Ni5 + x wt% Nd2O3 (x = 0, 0.5, 1, 1.5, 2, 3) composite coatings were prepared by laser cladding on the AZ91D Mg alloy. The coatings were composed of dendrites, cellular grains, Nd enriched spherical structure and amorphous matrix. Appropriate Nd2O3 addition can refine the size of crystalline microstructure, purify oxygen impurities and increase amorphous content of the coatings, but excessive addition of Nd2O3 (2-3 wt%) causes aggregation and abnormal growth of some crystalline phases and deteriorates the glass forming ability of the coatings. Corrosion resistance of the coating with 1.5 wt% Nd2O3 is the most excellent relying on the highest amorphous and the lowest crystalline phases contents in this coating. Wear resistance of the coatings is all greatly improved compared with the Mg substrate, however that are no linearly related to the hardness and do not follow completely the Archard's wear equation.