Complex Coating System for Improving Corrosion Resistance of Az31 Magnesium Alloy
5th International Conference “Innovative Materials, Structures and Technologies”: Abstract Book 2022
Paula Iesalniece, Reinis Drunka, Ints Šteins, Toms Valdemārs Eiduks, Konstantins Savkovs, Ilmārs Blumbergs

Nowadays aviation, aeronautics, transport, and construction material industries are searching for light metals and their alloys, that could be used to produce lighter products. Scientists are strongly looking at magnesium and its alloys, because they are up to 30% lighter than now widely used aluminium alloys. However, because of magnesium high chemical activity, it is subjected to corrosion, moreover a dense protective oxide layer does not naturally form on it, as it does in case of aluminium. The most effective corrosion protection for magnesium alloys produces methods, that create barrier layers, such as anodizing, plasma electrolytic oxidation (PEO) or chemical conversion. However, known corrosion protective methods of magnesium alloy do not give satisfying results, they are expensive and harmful to the environment, because they use compounds that contain Cr6+ and F- ions. [1,2] In this research a new environmentally friendly and cost-effective complex magnesium alloy AZ31 processing method, which includes 3 protective layer creation on the alloy surface, was developed. By using PEO method and a bipolar power source, in a low concentration electrolyte solution, a 7-15µm dense and amorph oxide layer with low porosity was obtained. This layer was at the same time modified with Zr, Si and P to further improve corrosion protective layer durability and mechanical properties. Because in the PEO process obtained samples are porous and corrosion usually starts in the pores, it is necessary to fill these pores. For this purpose, we chose spray pyrolysis method which allows to cover samples surface with a dense oxide layer, by rapidly evaporating and crystallizing reaction salt solution when it is sprayed on heated magnesium alloy surface. To obtain TiO2 coating with spray pyrolysis method, titanium isopropoxide solution was used and the processed AZ31 alloy surface was heated to 200o C, that provides proper TiO2 adhesion properties. The influence of pray pyrolysis process duration on corrosion resistance was investigated. 5th International Conference “Innovative Materials, Structures and Technologies” 80 In the third stage a polyurethane layer was obtained with spray gun that provides additional protection against corrosion. The selected paint system guarantees high adhesion and elasticity that does not allow microcracks to form. To evaluate samples corrosion resistance properties, obtained samples were immersed in 3% NaCl solution for 168h and after that surface was analyzed by using scanning electron microscope. It was concluded that the developed protective layer system successfully protects magnesium alloys from corrosion.

Magnesium alloy, corrosion resistance, PEO, plasma electrolytic oxidation

Iesalniece, P., Drunka, R., Šteins, I., Eiduks, T., Savkovs, K., Blumbergs, I. Complex Coating System for Improving Corrosion Resistance of Az31 Magnesium Alloy. In: 5th International Conference “Innovative Materials, Structures and Technologies”: Abstract Book, Latvia, Riga, 28-30 September, 2022. Riga: RTU Press, 2022, pp.79-80.

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