Difference in formation of plasma electrolytic oxidation coatings on MgLi alloy in comparison with pure Mg

Abstract

In order to study the substrate lattice structure (Li addition) on the growth of plasma electrolytic oxidation (PEO) coatings, MgLi alloy (11.36 wt.% of Li, cubic) and pure Mg (hexagonal) were treated under a pulsed direct PEO mode in a phosphate electrolyte for different periods of time. The results revealed that the presence of Li and Li-rich phases in the cubic Mg alloy seems to be essential for the treatment result rather than the original lattice structure. A modified discharge behavior of MgLi alloy finally led to a different microstructure of the coating. The unstable coatings of MgLi alloy tended to dissolve rapidly though shared the similar composition to that of pure Mg. Li was incorporated only in the primary conversion products at the interface of coating/MgLi. In spite of the advanced efficiency of energy input during processing, the more porous and thinner PEO coatings on the MgLi alloy were less resistant to abrasion and corrosion.