Investigation on surface properties of AZ31 magnesium alloy modified by micro-arc oxidation and cathodic deposition techniques

Abstract

Cathodic deposition (CD) technology, as a surface treatment technology, is widely used to prepare surface protective layers of non-valve metals. However, due to the presence of a dense oxide film on the surface of valve metal, during the CD process, this dense oxide film will hinder the contact between ions in the electrolyte and the substrate surface, making CD deposition technology unsuitable for valve metal. In this paper, valve metal AZ31 Mg alloy was first treated by micro-arc oxidation (MAO) technology, and then CD treatment was performed using ethylene glycol organic solution as electrolyte. This method not only solves the problem that CD technology cannot be applied to valve metals and successfully prepares a coating with excellent friction and corrosion resistance, but also explores a new solution as a CD electrolyte. By comparing with the samples after CD treatment in deionized water solution and the samples after MAO, the results show that after CD treatment in deionized water solution, only the porosity (8.572 %) and coefficient of friction (COF) (0.403) of the coating were improved, but after CD treatment in ethylene glycol solution, the coating surface had the lowest porosity (4.263 %), the highest hardness (265.2 HV), and the smallest COF (0.362). Electrochemical tests further showed that the sample had the lowest corrosion current density (5.6099 × 10⁻¹⁰ A/cm²) after CD treatment in ethylene glycol electrolyte. The coating prepared by this method can be widely used in aerospace, medical equipment and other fields due to their excellent friction and corrosion resistance, and can increase the service life of Mg alloy parts. However, this method is currently more suitable for the processing of small parts. This study not only provides a valuable strategy for improving the performance of MAO coatings, but also provides a new direction for the application of CD technology on valve metals.