Effect of phosphate additive on the morphology and anti-corrosion performance of plasma electrolytic oxidation coatings on magnesium―lithium alloy

•Two oxide coatings were prepared on dual-phase magnesium–8.5lithium alloy.•The properties of the two oxide coatings were investigated.•The coating prepared with addition of phosphate additive shows superior corrosion resistance. The widespread use of magnesium―lithium (Mg―Li) alloys is frequently hampered by the grand challenge associated with their high propensity to corrosion. Herein, we describe a method to access anti-corrosion coatings on Mg―8.5Li alloy employing plasma electrolytic oxidation (PEO) technique with phosphate additive. Our results reveal the oxide coating has a compact and uniform structure after 10-min PEO treatment, along with higher thickness (˜28 μm), hardness, and wettability (28°). Electrochemical measurements demonstrate the coating endows a significant enhancement in corrosion resistance for the Mg―8.5Li alloy along with a decent long-term protection for 300 h.