Corrosion protection of Zn–Al–Mg‐coated steel by a layered double hydroxide conversion layer

Abstract

Conversion layers produced on an industrial scale are typically based on phosphates or chromates and involve toxicological and environmental problematic treatment solutions and waste. Concerning this matter, layered double hydroxide (LDH)-based conversion layers prepared by the process described in our study offer a promising alternative where the treatment solution comes with no environmental or toxicological concerns. The corrosion protection of Zn–Al–Mg (ZM)-coated steel by an in situ grown LDH conversion layer is investigated by potentiodynamic polarization measurements, linear polarization resistance determination, neutral salt spray test and mass loss test. An LDH layer formation time as short as 30 s considerably improves the corrosion resistance of ZM-coated steel in electrochemical testing as well as in industrially relevant corrosion testing under chloride-containing atmospheres. With prolonged LDH formation times, further improvement in corrosion protection is obtained. The significantly increased corrosion resistance of ZM-coated steel after the industrially feasible treatment time of 30 s makes LDH-based conversion layers a promising candidate for novel industrially viable conversion layers, with enhanced corrosion performance and environmentally benign as well as sustainable chemistry.