ANALYSIS OF PHASE DISTRIBUTION FOR CERAMIC COATINGS FORMED BY MICROARC OXIDATION ON ALUMINUM-ALLOY

The phase distribution for ceramic coatings formed by microarc oxidati on (MAO) on 2024 aluminum alloy was investigated using X-ray diffracti on. The results showed that the ceramic coatings mainly consisted of a lpha-Al2O3 and gamma-Al2O3 phases. The percentage of alpha-Al2O3 gradu ally increased from the external surface to the interface between the coating and the substrate of samples. The surface layer of coatings ma inly contained the gamma-Al2O3 phase, and its fraction of the composit ion remained ahnost constant with oxidation time. It is believed that the difference in the amounts of alpha-Al2O3 and gamma-Al2O3 phases in the different layers of coatings was caused by the various cooling ra tes of molten Al2O3, which temporarily existed in the microarc zone.