Characterisation of Li in the surface film of a corrosion resistant Mg-Li(-Al-Y-Zr) alloy

TL;DR

This study investigates the composition and distribution of elements in the surface film of a corrosion-resistant Mg-Li-Al-Y-Zr alloy, revealing key compounds and elemental distributions that influence its corrosion resistance.

Contribution

It provides detailed characterization of the surface film and elemental distribution on a Mg-Li alloy, highlighting the roles of Li2CO3 and Mg(OH)2 in corrosion resistance.

Findings

Li is distributed throughout the surface film with higher concentration in the outer layer.

Principal surface film components are Li2CO3 and Mg(OH)2.

Presence of hcp grains near the surface was observed.

Abstract

The surface film formed upon Mg-Li(-Al-Y-Zr) following aqueous immersion and air-exposure was investigated. This alloy (which contains 30.3 at. % Li) possesses a bcc crystal structure and has been reported as being corrosion resistant. It was determined that the principal components of the surface film were Li2CO3 and Mg(OH)2 as characterised by grazing incidence X-ray diffraction (GIXRD). The detection of hcp grains near the alloy surface was observed by GIXRD and selected area electron diffraction (SAED). The spatial distribution of Li and Mg in the surface film was characterised by electron energy loss spectroscopy (EELS) and the distribution of other major elements in the alloy was characterised by scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDXS). It was observed that Li was distributed throughout the alloy surface film and with an elevated concentration in the so-called outer layer.