Surface modification of ACM522 magnesium alloy by plasma electrolytic oxidation in phosphate electrolyte

Plasma electrolytic oxidation (PEO) on a newly designed ACM522 magnesium die-casting alloy has been conducted in an aqueous phosphate solution and the morphology and corrosion resistance of the PEO films were investigated in detail. By covering the whole surface of the substrate with the PEO film, the corrosion resistance was significantly improved; the modified surface endured a salt spray test for 168 h. It was also clarified that traces of local breakdown caused by excessive PEO can be a cause of pitting corrosion, resulting in significant decline in corrosion resistance with PEO time.

► We studied plasma electrolytic oxidation (PEO) for a new magnesium alloy, ACM522.
► Covering whole ACM522 surface with PEO film greatly improved corrosion resistance.
► However, excessive PEO causes pitting corrosion.
► Corrosion resistance changes with PEO time because of defects in PEO films.