Characterization of microstructure and corrosion properties of AZ91D magnesium alloy surface-treated by coating-nitriding
Fuyao Yan, Baofeng Chen, Jiawei Yao, Danli Zhang, Mufu Yan, Yanxiang Zhang
Abstract
AZ91D magnesium alloy coated with magnetron sputtered alternating Al/Ti multilayer was plasma nitrided at different temperatures, and the changes of its microstructure and corrosion properties were investigated. Compared with the pre-coated specimen, it was shown that the microhardness and corrosion resistance of the coated AZ91D magnesium alloy after nitriding treatment are improved significantly. In addition, the surface hardness was promoted to more than twice that of the substrate, and corrosion potential shows a significant positive shift. The improvement in hardness is attributed to solid solution strengthening by nitrogen atoms, the precipitation strengthening of Al3Ti and Ti2N phases in the Al/Ti multilayer coatings and with the superficial layer of the alloy substrate during nitridation. The best performance was obtained by nitriding at 375 °C over the pre-coated alternate Ti/Al multilayer structure. The coating-nitriding duplex treatment of AZ91D magnesium alloy can produce a high-quality, dense and diffusive composite surface layer that has a strong bonding with the magnesium alloy substrate and results in excellent microhardness and corrosion resistance.