Lanthanum-based conversion coating on Mg–8Li alloy

The lanthanum-based conversion coating on Mg–8Li alloy was investigated and the corrosion resistance was evaluated as well. The surface and cross-sectional morphology were observed by scanning electron microscopy (SEM), and composition of the lanthanum conversion coating was characterized by energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The corrosion resistance was assessed by means of potentiodynamic polarization measurements and open circuit potential (OCP). The results revealed that the conversion coating was homogeneous and uniform, and had an aciculate-like structure. The coating exhibited good adhesion to substrate with thickness of about 10 μm, and it was mainly composed of La(OH)3 as identified by XPS, consistent with compositional analysis using EDS. The electrochemical results revealed that the lanthanum-based conversion coating possessed better corrosion resistance than the Mg–8Li substrate.