Microstructure, corrosion and wear resistances of microarc oxidation coating on Al alloy 7075

Microarc oxidation (MAO), an important surface treatment technology for Al alloys in stead of hard anodization, was applied to prepare coating on Al alloy 7075, of which the microstructure and properties of the anti-corrosion and anti-wear were studied by XRD, SEM, neutral salt spray (NSS) test and ball-on-disc friction and wear test. The results show that the MAO coating formed on Al alloy 7075 mainly consists of γ-Al2O3, α-Al2O3 and some amorphous SiO2. Si element results from electrolyte or from substrate. MAO coating exhibits excellent corrosion resistance, for example, coatings with thickness of 70 μm can endure more than 2000 h in NSS test even without seal treatment. Dense microstructure of MAO coating results in the excellent corrosion resistance. Post seal treatment can greatly enhance the corrosion resistance of the MAO coating, even for thin coating. MAO coating fabricated on Al alloy 7075 possesses similar friction coefficient but much higher wear resistance compared with hard anodized film, for example, the former is as 50 times as the wear resistance of the later. The MAO coating is just slightly worn and its frication coefficient remains unchanged throughout the test. © Copyright.