LDH sealing for PEO coated friction stir welded AZ31/AA5754 materials

The need to combine various metals in light-weight constructions requires the development of coatings that prevent galvanic corrosion. Layered double hydroxides (LDHs) can be an example of such coatings, which were previously successfully obtained in situ on individual materials. In addition, the possibility of LDH growth (including LDH growth in the presence of chelating agents) on the surface of plasma electrolytic oxidation (PEO)-coated metals was previously shown. This PEO ​+ ​LDH combination could improve both corrosion and mechanical characteristics of the system. The possibility of LDHs formation in situ on the surface of PEO-coated friction stir welded (FSW) magnesium-aluminum materials (AZ31/AA5754 system was selected as a model one) was demonstrated in the presence of 1,3-diamino-2-hydroxypropane-N,N,N’,N’-tetraacetic acid (DHPTA) as a chelating agent, which was selected based on analysis of respective metal-ligand compounds stability. LDHs growth was achieved under ambient pressure without addition of carbonates in the electrolyte. The effectiveness of the resulting coating is shown both for corrosion resistance and hardness.