A study to enhance the mechanical durability of the MAO coating fabricated on the 7075 Al alloy for wear-related high temperature applications

This work has been initiated with the aim of increasing the success of micro-arc oxidation coatings fabricated on aluminium alloys against degradation under sliding contact conditions at high temperatures. For this purpose, the 7075 Al alloy has been micro-arc oxidised in an aluminate-based electrolyte with or without the adding monoclinic ZrO₂ particles. Microstructural analyses revealed that the coating synthesised in a ZrO₂-added electrolyte consisted of a ZrO₂ particles participated Al₂O₃-based outer layer and a monolithic Al₂O₃-based inner layer, which exhibited similar features with that of the synthesised in the ZrO₂-free aluminate-based electrolyte. Moreover, the coating fabricated in the ZrO₂-added electrolyte exhibited enhanced wear resistance during the dry sliding wear tests conducted at room temperature and had higher durability during the tests done at 300 °C. Since the examined coatings were worn by fatigue wear mechanism, their durability during high temperature wear tests was analysed by using the conventional stress-based fatigue approach. From the derived equations, the maximum contact pressures at which coatings can endure 10⁶ contact cycles at 300 °C were estimated as 851 and 331 MPa for the coatings fabricated in the ZrO₂-added and ZrO₂-free aluminate-based electrolytes, respectively.