Corrosion and Mechanical Behavior of Plasma Electrolytic Oxidation Coated Al Alloy

Alumina coating was deposited as a protective layer on Al alloy by plasma electrolytic oxidation (PEO) process under unconventionally high applied voltage and high SiO32− concentration. Scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX) was used to analyze the microstructure and thickness of the coating. Corrosion, hardness and adhesion properties linked to its protective performance were studied by linear polarization, nano-indentation and ASTM D3359 adhesion test. The high voltage contributed to the formation of ceramic coating consisting of α-phase Al2O3 and mullite. Due to the compact crystalized structure produced by PEO, the corrosion resistance was significantly improved. The proposed coating also exhibited high hardness and excellent adhesive strength.