Micro-Arcs Oxidation Layer Formation on Aluminium and Coatings Tribological Properties—A Review

This review proposes to carry out a state-of-the-art associated with micro-arc oxidation. Firstly, the different aspects of the growth mechanisms of the oxides are detailed. Then, the formation of micro-arcs and the case of soft-spark treatment are discussed. Then, the electrolytic reactions involved in the layer construction are outlined. We focused on the influence of aluminium alloys on the appearance of the coating and its characteristics before considering the electrolyte formulation. We have concentrated some of our efforts on silicate-based electrolytes, mainly used in research and industry. The importance of electrical parameters in layer formation is detailed later. The main factors studied in the literature are the current source, current density, treatment frequency and duration, and duty cycle. We have also noted the different phase compositions identified in the literature. Finally, since the process is particularly advantageous for protecting the surfaces of aluminium parts against wear, we conclude this review by presenting work on the tribological properties of this coating. In this final section, we highlight the work on the wear-reducing properties and tribological mechanisms identified in the literature. Particular attention is paid to the relationship between the nature of the substrates used, the role of the electrolyte and the counterpart choice on the friction and wear results.