Effect of Sn and Mn Composite Addition on Microstructure and Properties of Micro-arc Oxidation Coating on AZ21 Alloy

Abstract:

The effects of low-cost Sn (1wt%) and Mn (0.5wt%) composite addition on the microstructure and properties of micro-arc oxidation coatings on extruded Mg-2Al-Zn (AZ21) alloy were studied. After the addition of Sn and Mn elements to the substrate, the phase composition of the coatings remains unchanged, mainly consisting of MgO, MgAl₂O₄ and AlPO₄ phases. The thickness and porosity of the coatings increase slightly, the thickness increases from 8.49 μm to 9.60 μm, and the porosity increases from 5.05% to 5.75%. The wear resistance and corrosion resistance of the substrates and coatings were evaluated by dry friction and wear test, immersion test and potentiodynamic polarization test. The results show that the micro-arc oxidation coating significantly improves the wear resistance and corrosion resistance of the substrate. The composite addition of Sn and Mn improves the wear resistance of the coatings, but their corrosion resistance decreases. The wear rate of the coating decreases from 3.53×10^-5 mm³·(N·m)^-1 to 2.993×10^-5 mm³·(N·m)^-1. The corrosion current density of the coating increases from 3.14×10^-6 A·cm^-2 to 4.18×10^-6 A·cm^-2.