Electrochemical Properties of Plasma-Electrolytically Oxidized Aluminum Coatings Sprayed on MA5 Magnesium Alloy

The aluminum-based coating was sprayed onto a substrate made of MA5 magnesium alloy by detonation and thermal vacuum methods. Potentiodynamic polarization studies were carried out to evaluate corrosion resistance of the modified surfaces. Thermal vacuum coating is non-porous, but thin (approx. 50 μm). The plasma-electrolytic oxidation (PEO) layer of the aluminum coating almost does not interact with the magnesium base during the process of synthesizing the oxide ceramic coating. The corrosion resistance of the detonation coating was twice as high as that of the MA5 magnesium alloy, but the layer synthesized on the PEO coating neutralized this effect. This is related with the growth of the PEO layer through the sprayed coating (thickness approx. 200 μm) to the base and the presence of through pores in it, which over time causes the spalling of such a combined coating. The opposite electrochemical picture is observed on the surface of the thermal vacuum sprayed coating without and with the presence of the PEO layer on it. Here the corrosion currents are lower in 25 times and by 2 orders of magnitude, respectively. Such a significant difference in the corrosion resistance of aluminum coatings is caused by their porosity and structural defects due to the peculiarities of the technological process.