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 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 (~ 50 mm). In the process of synthesizing the oxide ceramic coating, the plasma-electrolyte oxidation (PEO) layer of the aluminum coating almost does not interact with the magnesium base. It was found that 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 due to the growth of the PEO layer through the sprayed coating (thickness ~ 200 mm) to the base and the presence of through pores in it, which over time causes the peeling of such a combined coating. The opposite electrochemical picture can be observed on the surface of the thermal vacuum sprayed coating without and with the presence of a peo layer on it. Here, the corrosion currents are lower by 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 defects in the structure, which is due to the peculiarities of the technolo­gical process.