Mechanical properties of Al2O3 ceramic coatings prepared by plasma spraying on magnesium alloy

An Al2O3 coating has been successfully prepared on an AZ91HP magnesium (Mg) alloy by plasma spraying technology. Al-Si eutectic alloy was used as the transition layer in order to ease the physical and chemical differences between the Al2O3 and the Mg alloy. The mechanical properties of the coating were studied. The results show that the coating consists mainly of stable α-Al2O3 and metastable γ-Al2O3 phases, with a lamellar microstructure. Nano-indentation results exhibit that the peak loads of the plasma-sprayed Al2O3 layer, the Al-Si transition layer, and the Mg alloy are 2.2, 0.6 and 0.25 mN, respectively. The elastic modulus and microhardness of the plasma-sprayed Al2O3 layer are 250 and 7.45-8.90 GPa, respectively, which are higher than those of the Mg alloy (50 and 0.8 GPa). The wear volume of the plasma-sprayed Al2O3 coating is two orders of magnitude smaller than that of the Mg alloy.