Micro-arc oxidation (MAO)-also known as plasma electrolytic oxidation (PEO)-is a technology that utilizes micro-arc discharges generated on the surfaces of valve metals (such as aluminum, magnesium, and titanium) to trigger complex physicochemical reactions between the metal substrate and elements within the electrolyte, ultimately forming a ceramic layer composed primarily of the metal substrate's oxides.
During the micro-arc oxidation process, the discharge voltage exceeds the range typical of conventional anodizing. When the applied voltage rises from the tens of volts used in anodizing to hundreds of volts-surpassing the dielectric breakdown strength of the surface passivation layer-arc discharge occurs. This phenomenon is accompanied by the melting of the metal substrate and the ionization of electrolyte molecules, with instantaneous temperatures reaching as high as 10,000 K. The process involves complex physicochemical reactions that result in the *in situ* formation of a ceramic layer-composed mainly of metal substrate oxides-on the outer surface of the substrate. This ceramic layer bonds metallurgically with the metal substrate, significantly enhancing properties such as the workpiece's corrosion resistance, wear resistance, and hardness.
