Design of corrosion-resistant Mg-Zn/Gd-X alloys: Insights from theoretical calculations and experimental studies

Abstract

The effects of various elements on the corrosion behavior of Mg-Zn/Gd alloy systems were systematically studied using first-principles and thermodynamic calculations. Based on the findings, guidelines for selecting elements to design corrosion-resistant Mg-Zn/Gd-X alloys were proposed. According to the element effects, it was firstly proposed that the Mg-Zn alloy system with the solid solution of f-electron elements or Ca of s-electron elements could deliver good corrosion resistance, and the Mg-Gd alloy system with the solid solution of p-electron elements could deliver good corrosion resistance. Furthermore, in consideration of the ability of X to form corresponding protective films and the solid solution behavior of Zn/Gd-X in α-Mg phase, it was eventually proposed that certain element combinations in solid solution, e.g. Zn-Sc, Zn-Er, Zn-Ho, Gd-Sc, Gd-Sn, and Gd-Ga show promise for enhancing corrosion resistance, since these element combinations show the ability to retard the anodic dissolution and cathodic HER reactions, promote the formation of composite compact protective films, and maximum the beneficial effects of elements. Key experimental results demonstrated that the designed Mg-0.5Zn-0.5Sc and Mg-0.5Gd-0.5Sc (at%) alloys exhibit good corrosion resistance, with corrosion rates approximately three orders of magnitude lower than that of pure Mg used in this study and obviously lower than those of Mg-Zn and Mg-Gd binary alloys reported in the literatures. This work provides the insights into the design of corrosion-resistant Mg-Zn/Gd-X alloys, which can be also applied in the design of other corrosion-resistant Mg alloy systems.