Microstructure and mechanical properties near interface between microarc oxidation coating and Al alloy substrate

The microstructure near the interface between a 2024 Al alloy substrate and a ceramic coating formed by microarc oxidation has been studied using scanning electron microscopy and energy dispersive spectrometry. Hardness and elastic modulus on the two sides of the interface were investigated using nanoindentation and Vickers microhardness measurement. The results showed that the microstructure of the substrate was not changed by application of the coating, and a hardened zone was not observed. During microarc oxidation, no remelting of the substrate occurred, but remelting of the alumina ceramic coating on the other side of the interface did take place. The mechanical properties on the two sides of the interface had obvious differences: in a certain range of coating thickness there was a gradual increase of hardness and elastic modulus from the interface to the interior of the coating, but hardness remained almost constant in the substrate.