The effect of PEO parameters on the properties of biodegradable Mg alloys: a review

Abstract

This paper comprehensively reviews recent research carried out in the field of preparation of bioactive coatings on magnesium (Mg)–aluminum (Al)–zinc (Zn) alloys by using the plasma electrolytic oxidation (PEO) method and investigation of factors affecting it. Magnesium–aluminum–zinc alloys (AZ grades) have been developed for use as biodegradation materials because the addition of aluminum and zinc as alloying elements can ameliorate their mechanical properties and increase corrosion resistance over those of pure magnesium alone without decrement in biocompatibility. Among the common methods for improvement of biodegradation, corrosion resistance and biocompatibility of magnesium alloys, surface modification techniques have been more effective. PEO is a relatively novel surface modification technique that provides excellent wear- and corrosion-resistant coatings on lightweight metals, in particular on magnesium and its alloys. The processing parameters of PEO, such as pulse frequencies, applied voltages, oxidation time, electrolyte concentrations and substrate chemical composition, are some of the major factors that determine the quality of the coatings in terms of corrosion resistance and bioactivity in body fluid solutions. Considering the fact that comprehensive review articles on the effect of PEO parameters on the properties of magnesium alloys have not been published in recent years, the aim of the present text is to provide an understanding of all aspects of these process parameters.