Wear and corrosion resistant coatings on surface of cast A356 aluminum alloy by plasma electrolytic oxidation in moderately concentrated aluminate electrolytes
(College of Materials Science and Engineering, Hunan University, Changsha 410082, China)
Abstract: Plasma electrolytic oxidation of a cast A356 aluminum alloy was carried out in aluminate electrolytes to develop wear and corrosion resistant coatings. Different concentrations of 2, 16 and 24 g/L NaAlO2 solutions and a silicate electrolyte (for comparison) were employed for the investigation. Wear performance and corrosion resistance of the coatings were evaluated by WC (tungsten carbide) ball-on-flat dry sliding tests and electrochemical methods, respectively. The results show that the coating formed for a short duration of 480 s in 24 g/L NaAlO2 solution generated the best protection. The coating sustained 30 N load for sliding time of 1800 s, showing very low wear rate of ~4.5×10-7 mm3/(N·m). A low corrosion current density of ~8.81×10-9 A/cm2 was also recorded. Despite low α-Al2O3 content of the coating, the compact and nearly single layer nature of the coating guaranteed the excellent performances.
Key words: A356 aluminium alloy; sodium aluminate; plasma electrolytic oxidation; wear; corrosion