Corrosion behavior and mechanism of Mg–Er–Zn–Zr alloys in different states
Jinshu Xie, Jinghuai Zhang, Zhi Zhang, Xin Qiu, Han Zhang, Haodong Zhang, Xingkai Jiao, Xiaohan Wu, Ruizhi Wu
Abstract
The corrosion behavior and mechanism of as-cast, solid-solution treated, and as-extruded Mg-14.4Er-1.4Zn-0.3Zr (wt.%) alloys are investigated. The microstructure characteristic of as-cast alloy, i.e., the semi-continuous 18R-long period stacking ordered (LPSO) phase as cathode with the potential difference (PD) of 83 mV, is the main reason for the relatively strong tendency of micro-galvanic corrosion. The lower micro-galvanic tendency by the decreased size, number, and PD (30 mV) of LPSO-phase particles, and the existence of a few Er3+ in corrosion film, are mainly responsible for the improved corrosion resistance of solid-solution treated alloy. The as-extruded alloy exhibits a superior corrosion resistance (corrosion rate: 1.11 mm y−1 in 3.5 wt.% NaCl solution) as compared to many reported Mg alloys, which mainly attributed to the formation of nano-spaced basal plane solute-enriched stacking faults (SESFs) within fine dynamic recrystallized (DRXed) grains. The nano-scale SESFs as the weak anode with PD of 26 mV weaken the galvanic tendency to form a relatively homogeneously electrochemical microstructure. Moreover, the preferential corrosion of SESFs releases sufficient Er3+, promoting the quasi-passivation state of corrosion film. The construction of weak anodic nano-lamellar SESFs structure within fine grains is a feasible method for the synergetic improvement of strength and corrosion resistance of Mg alloys.