Enhanced corrosion resistance of ultrafine-grained Mg–Zn–Gd alloy produced by surface sliding friction treatment

In this work, an ultrafine-grained (UFG) structure with an average grain size of 122 nm was successfully fabricated in the Mg–2Zn–0.8Gd (wt.%) alloy via surface sliding friction treatment (SFT). The microstructural evolution and the corrosion behavior of SFTed Mg–2Zn–0.8Gd (wt.%) alloy plate were investigated. Electrochemical tests reveal that the UFG surface exhibits a higher impedance than that of the starting coarse-grained (CG) structure. The corrosion rate of the UFG specimen declines from 5.78 mm·y −1 (for CG specimen) to 4.51 mm·y −1 after SFT processing, representing an approximate 22% reduction in corrosion rate. The enhanced corrosion resistance originates from two key factors: (1) The high-density grain boundaries in the UFG layer can promote the stability of corrosion product films, which exhibit better compactness and less crack tendency compared to the CG specimen. (2) SFT processing induces the rearrangement of second-phase particles (Mg-Zn and Mg-Zn-Gd phases), which weakens the galvanic corrosion. This work reveals the corrosion behavior of the UFG-structured Mg alloy, providing a novel method to enhance the corrosion resistance of Mg alloys.