Effect of microstructure refinement on the corrosion of AZ91D magnesium alloys
LIU Qu, CHEN Gaoqiang, ZENG Shenbo, ZHANG Shuai, PAN Jiluan, SHI Qingyu
Key Laboratory for Advanced Materials Processing Technology of Ministry of Education, State Key Laboratory of Tribology, Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China
Abstract：The poor corrosion resistance of magnesium alloys in aqueous solution containing electrolyte significantly restricts their engineering application. In this paper, with the aim of developing a new processing technique to efficiently improve the corrosion resistance of magnesium alloy, friction stir processing (FSP) was applied to modify the corrosion resistance of cast AZ91 magnesium alloy. And the effect of microstructural refinement on the corrosion resistance was investigated. The electrochemical measurements reveal that the polarization impendence Rp of processed alloy in NaCl solution with a mass fraction of 3.5% is nearly doubled. The results of microstructure analysis show that it is mainly attributed to the alteration of corrosion process induced by modification on the morphology and distribution of β-Mg17Al12 phase in magnesium alloys. On the one hand, the refinement of cathodic β-Mg17Al12 phase increases the area ratio of anode and cathode, which mitigates the severe galvanic corrosion in magnesium alloys. On the other hand, a large amount of fine β-Mg17Al12 particles could redeposit on the surface of magnesium alloy to form protective layer during corrosion and significantly inhibit the propagation of corrosion into α-Mg matrix.