Investigating the structure of the surface film on a corrosion resistant Mg-Li(-Al-Y-Zr) alloy

The surface film formed on an ultra-lightweight Mg-Li(-Al-Y-Zr) alloy was investigated. Previous research reported that this body-centered cubic (bcc) Mg-Li(-Al-Y-Zr) alloy demonstrated high corrosion resistance that was associated with the formation of a protective lithium carbonate (Li2CO3) surface film. Herein, the surface film that forms upon the bcc Mg-Li(-Al-Y-Zr) alloy following exposure to aqueous chloride containing electrolyte and ambient air was comprehensively studied by complementary methods, to provide a holistic representation of the alloy surface composition and structure. In addition to scanning electron microscopy and transmission electron microscopy of focused ion beam prepared surface cross sections, the composition of the surface film was studied by grazing incidence x-ray diffraction and Raman spectroscopy, both of which revealed Li2CO3 formation on the surface. The surface film structure was also investigated by glow discharge optical emission spectroscopy. The results indicated that a complex and multilayer surface film formed upon Mg-Li(-Al-Y-Zr) following air exposure and when studied ex situ.