Effect of additive Al2O3 powders on micro-arc oxide coating of magnesium alloy

In order to understand the effect of additive Al2O3 powders on the film corrosion resistance and the microstructure of the micro-arc oxide (MAO) ceramic film of magnesium alloy, AZ91D die cast magnesium alloy was oxidized with a special micro-arc apparatus. Morphological characteristics and phase constituent of ceramic coatings were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD). And the aluminum (Al) element of before and after the Al2O3 accession were analyzed by energy-dispersive X-ray (EDX). The results showed that after adding Al2O3 powders, pores on ceramic coatings decreased, the loose layer became more compact, the new phase of Al2O3 appeared, and the Al element of the ceramic membrane increased. Ultrasonic waves promoted the content of Al2O3 in the layer. Electrochemical corrosion experiments in 3.5% NaCl solution showed that the corrosion resistance of ceramic coatings after adding Al2O3 powders was improved greatly.