Micro and nano-enabled approaches to improve the performance of plasma electrolytic oxidation coated magnesium alloys

Magnesium (Mg) and its alloys have become a hot research topic in various industries owing to the specific physical and chemical properties. However, high corrosion rate is considered the key lifetime-limiting. Plasma electrolytic oxidation (PEO) method is a simple strategy to deposit an oxide layer on the surface of light metals such as magnesium alloys, to control corrosion rate and promote some other properties, depending on their performances. Nevertheless, their features including their micropore size, distribution, and interconnectivity, and microcracks have not been improved to an acceptable level to support long-term performances of the magnesium-based substrates. Studies have introduced micro/nano-enabled approaches to enhance various properties of PEO coatings such as corrosion resistance, tribological properties, self-healing ability, bioactivity, biocompatibility, antibacterial properties, or catalytic performances. These strategies consist of incorporating of micro and nanoparticles into the PEO layers to produce multi-functional surfaces or the formation of multi-layered coatings to cover the defects of PEO coatings. In this perspective, the present paper aims to overview various nano/micro-enabled strategies to promote the properties of PEO coatings on magnesium alloys. The main focus is given to the functional changes that occurred in response to the incorporation of various types of nano/micro-structures into the PEO coatings on magnesium alloys.