Plasma electrolytic oxidation treatments for bimetallic substrates enabling sustainable procedures for automotive painting

Magnesium- or Aluminium based lightweight alloys are increasingly utilized in the automotive sector. To ensure corrosion protection of these lightweight alloys, plasma electrolytic oxidation (PEO) can be utilized to from protective layers in an efficient manner on those lightweight alloy materials. In real vehicles often a blend of joined materials is used and it must be evaluated if the joined material combinations can be subjected directly to corrosion protection treatments or if separated treatments are necessary for different materials, which would significantly enhance production costs. In this study we investigate the feasibility of the PEO process for already joined Al-alloy and Mg-alloy materials. Special focus is put on the compatibility with subsequent cathodic dip coating (CDC) processes and the corrosion resistance of the coated materials was evaluated, which is highly relevant for applications in vehicles. We provide characterization of the formed PEO layers and could demonstrate different layer formation behaviour and composition, depending on the alloy material. It could be also shown that Mg-alloy and Al-alloy materials joined by gluing and riveting can be subjected to the PEO process, resulting in effective, simultaneous protective layer formation on both materials. Finally, it is demonstrated that the joined and PEO treated materials exhibit excellent compatibility with the cathodic dip coating process and that previous PEO treatment results in better corrosion resistance also for cathodic dip coated samples.