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

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 body-centred cubic (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). Hexagonal close-packed (hcp) grains near the alloy surface were detected 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.