Atomic Insight into the Influence of Y Content on the Corrosion Resistance of Az91 Magnesium Alloy Based on First-Principles Calculations

Abstract

Micro-alloying Mg-Al-Zn (AZ-series) alloys with different rare earth (RE) elements to enhance their corrosion resistance is being widely studied, but the optimal amount of RE elements is hardly determined. Therefore, with the aim of serving as shell of lithium-ion battery pack systems (BPS), the typical commercial AZ91 magnesium alloy was first micro-alloyed with 0.5 and 1 wt.% Y element, and then their stress corrosion cracking (SCC) and corrosion resistances in a 1 mol/L LiPF6 electrolyte solution were studied. Further, the influence of Y content on the corrosion resistance of AZ91 magnesium alloy was revealed based on microstructural characterization and first-principles calculations. The results showed that the corrosion and SCC resistances of AZ91 alloy were both improved. This is because the addition of Y could effectively decrease the volume fraction of the β-Mg17Al12 phase which has higher work function and lower adsorption energy of H atoms than Mg matrix, thereby weakening the effect of hydrogen embrittlement (HE) and micro-galvanic corrosion phenomenon between Mg matrix and β-Mg17Al12. However, the differences in work function (∆Φ) and adsorption energy of H atoms between Al2Y phase and Mg matrix are higher than those between β-Mg17Al12 phases and Mg matrix. Therefore, the higher content of Al2Y phase in AZ91-1Y alloy results in lower corrosion and SCC resistances compared with AZ91-0.5Y alloy.

Keywords: Magnesium alloy, Rare earth elements, Stress corrosion cracking, Corrosion resistance, First principles calculation