Studies on thermal oxidation of Mg-alloy (AZ91) for improving corrosion and wear resistance

The present investigation concerns development of an adherent stable oxide layer on the surface of a Mg alloy, AZ91 (8.3-9.7% Al, 0.13% Mn, 1.0% Zn, 0.50% Si, 0.10% Cu, 0.03% Ni, 0.30% other, balance Mg) by thermal oxidation to improve wear and corrosion resistance in simulated body fluid. Oxide layer was developed by thermal oxidation of freshly polished AZ91 samples in air at 200 °C, 300 °C and 400 °C for 8, 16 and 25 h. Following thermal oxidation, a detailed characterization of the oxide layer was undertaken in terms of microstructure and phases. The wear, corrosion resistance and biocompatibility were evaluated in details. The oxide layer mainly consists of oxides of magnesium (MgO2 and MgO) phases. The corrosion resistance (in simulated body fluid) and wear resistance of the oxidized surface were improved. Thermally oxidized Mg-Al alloy (AZ91) treated at 200 °C for 25 h have shown best biocompatibility in terms of cell (L-929 mouse fibroblast cell line) proliferation.