Fabricating a corrosion-protective Li2CO3/Mg(OH)2 composite film on LA141 magnesium‑lithium alloy by hydrothermal method

Abstract

Magnesium‑lithium (MgLi) alloys are currently the lightest metallic structural materials. However, their chemical activity is significantly increased by Li element which leads to poor corrosion resistance. The spontaneously formed Li2CO3 film in natural environments on MgLi alloy has a corrosive protection effect, however, it is not dense and thick enough and could only provide limited protection. In this study, a Li2CO3/Mg(OH)2 composite film was fabricated on LA141 MgLi alloy by using hydrothermal method to improve its corrosion resistance. The growth process of the film was observed by X-ray diffraction (XRD) and second electron microscope (SEM). The corrosion protection performance and failure mechanism of the film were investigated with electrochemical methods. The experimental results showed that the corrosion rate of the alloy was decreased by 98.93 % with the protection of the as-prepared film. The film had a bilayer structure: the inner layer was dense and had a higher Li2CO3/Mg(OH)2 ratio, and the outer layer was loose and had a lamellar structure with a lower Li2CO3/Mg(OH)2 ratio. The corrosion protection performance was mainly provided by the inner layer. During the failure process, the outer layer of the film first underwent uniform dissolution, followed by local damage on the inner layer.