Effect of low concentration electrolytes on the formation and corrosion resistance of PEO coatings on AM50 magnesium alloy.

• The formation process and corrosion properties of PEO coatings formed in phosphate, aluminate, and mix of phosphate and aluminate electrolytes have been systematically investigated. • Coatings prepared from single phosphate electrolytes and phosphate-aluminate low concentration electrolytes have greater potential than aluminate coatings based on microstructure and corrosion performance of layers. • In the case of low concentration solution, the thickness of aluminate-based coating cannot be significantly increased by increasing concentration of electrolyte. In this paper, the formation process, morphology, and electrochemical performance of PEO coatings on AM50 magnesium alloy prepared in low concentration phosphate, aluminate, and phosphate-aluminate electrolytes were systematically studied. The results show that the coatings prepared from the phosphate electrolytes have a higher thickness and better corrosion resistance properties compared to the other electrolytes. The coatings prepared from low concentration phosphate-aluminate mixed electrolytes have slightly thinner thickness, a similar coating structure and an order of magnitude lower value of electrochemical impedance compared with phosphate electrolyte coatings. The Coatings prepared from low concentration aluminate electrolytes have the lowest thickness and the worst corrosion resistance properties which gets close to corrosion behavior of the bare AM50 under the same test conditions. Considering application, coatings prepared from single low concentration phosphate electrolytes and low concentration phosphate-aluminate electrolytes have greater potential than single low concentration aluminate coatings. However, reducing the electrolyte concentrations of coating forming ions too much has negative influence on the coating growth rate. [ABSTRACT FROM AUTHOR]