Corrosion and Wear Enhancement of Composite Layers over PEO-Coated Mg Alloys: A Review

Magnesium alloys have garnered significant gained attention in the scientific community due to their low density, superior damping capacity, impressive strength-to-weight ratio, and recyclability. The biocompatible Mg alloys attracted the researchers to use them as permanent implants in the body. But Mg alloys were positioned low in the electromotive series, have a high affinity for corrosion, and will be degraded in the presence of corrosive anions. Surface modification methods could be adopted to protect the Mg surface from corrosive environments. Among various surface treatment processes, plasma electrolytic oxidation (PEO) process is environmentally friendly for providing a robust anti-corrosion and wear-resistant coating on the Mg alloys. Presence of the pores and cracks on the PEO surfaces reduced the corrosion and wear resistance of the alloys. Surface morphology, corrosion and wear characteristics of the PEO-coated Mg surfaces can be improved by various composite coatings. The mechanisms of corrosion inhibition, wear characteristics, wetting characteristics, biofunctionality and finally the degradation of various composite coatings over Mg‑PEO surfaces in the presence of corrosive environments are elaborated in this review paper.