Comparison on corrosion resistance and surface film of pure Mg and Mg-14Li alloy

To study different corrosion resistances and surface film types of hexagonal close-packed (HCP) pure Mg and body-centered cubic (BCC) Mg-14wt.%Li alloy in 0.1 mol/L NaCl, a series of experiments were conducted, including hydrogen evolution, mass loss, in-situ electrochemical testing combined with Raman spectroscopy and microstructural observation. The results indicate that the corrosion resistance of pure Mg is superior to that of Mg-14Li, and the protective function of the surface films on both magnesium systems is elevated within 16 h of immersion in 0.1 mol/L NaCl. An articulated, thick, and needle-like surface film containing Li2CO3 on Mg-14Li, different from the typically thin, flaky Mg(OH)(2) film on pure Mg, is confirmed via scanning electron microscopy (SEM). However, both surface films can be broken down at a high anodic over-potential. Thus, different corrosion resistances of the two Mg systems are ascribed to various protective films forming on their surfaces.