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Spray painting method for PEO coated AZ31 alloy

PEO process produces a porous layer of stable oxide of the substrate metal. Typically, this porous layer serves as a highly suitable surface for application of paint. The paint seals the pores of the PEO layer and offers added protection to the base material against corrosion. Application of polyurethane paint on PEO coated AZ31 specimens was performed in this study and optimum solvent volume was found for the primer and paint mixture.

The volume of solvent recommended by the manufacturer is 15 – 20 % of the paint volume, and it was varied between 20 – 70 % to obtain the optimum content for the current spray setup. It was found in this study that the best performance with the spray gun was obtained with solvent content equivalent to 35 % of the paint volume. This ratio produced the most uniform coating with highly repeatable results. For the primer, the manufacturer recommends 12.5 % solvent to primer volume, but it was found that the best results were obtained with 20 % volume ratio. Hence, for both the primer and paint the optimum volume fraction of solvent was more than the amount prescribed by the manufacturer.

Figure 1. Image of AZ31 specimen after (a) PEO coating, (b) with primer coating, and (c) PU paint coating.

Spray painting method was successfully employed for painting PEO coated AZ31 alloy. The optimum working viscosity for the spray gun was found by varying the solvent content from 20 – 70 % of the main component (paint and primer). It was found that the best spray coat was obtained with a mixture of 1:5 (20 %) solvent-to-primer and 7:20 (35 %) solvent-to-paint mixtures, which were higher than what was recommended by the manufacturer.



Being implemented with the financial support of the ERDF.


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