Wear and corrosion resistant coatings prepared on LY12 aluminum alloy by plasma electrolytic oxidation

Although aluminum alloys are widely used in the aerospace industry, their relatively poor wear and corrosion resistance have hampered some applications and reduce the lifetime of the components. In this work, by using a zinc-containing phosphate electrolyte, the corrosion resistance, surface hardness, and wear resistance of the coatings produced by plasma electrolytic oxidation (PEO) are simultaneously improved. The micro-arc discharge is optimized by changing the phosphate concentration instead of introducing hard phase cations to improve the crystallinity of the zinc-doped alumina coating. Our results reveal that by using a concentration of (NaPO₃)₆ of 50 g/L, the hard phase of crystralline alumina and corrosive-resistant phase of Zn₃(PO₄)₂ are produced in concert. In the salt spraying test, the lifetime of the PEO coating is over 5000 h and the electrochemical corrosion current density is reduced by about 2 orders of magnitude confirming the improved corrosion resistance and durability. Moreover, the surface hardness increases from 400 HV for the coating prepared using the conventional phosphate electrolyte to 711.8 HV and the wear rate also drops from 8.5 × 10⁻⁴ mm³·(N·m)⁻¹ to 2.0 × 10⁻⁵ mm³·(N·m)⁻¹. This strategy can guarantee the aluminum alloy PEO coating with simultaneous excellent wear and corrosion resistance to cope with the complex service environment.