Corrosion Protection Behavior of Aluminate Ion-Loaded Layered Double Hydroxide Coating on AZ31 Magnesium Alloy

Abstract

Effect of aluminate ion loading on the corrosion behavior of layered double hydroxide (LDH) coating of Mg-3Al-1Zn (AZ31) alloy was investigated. The corrosion inhibition performance of NaAlO2 for AZ31 was examined by immersion and polarization tests. Then, aluminate ion-loaded LDH (LDHAlO2) was synthesized from hydrotalcite (LDHCO3) and co-deposited with magnesium and aluminum double hydroxide on AZ31 by electrophoretic co-deposition. Polarization, electrochemical impedance (EI) and wet-dry cyclic corrosion tests were conducted on the LDHAlO2- and LDHCO3-coated specimens. Adding 10–50 mmol l−1 NaAlO2 to 0.1 mol l−1 NaCl solution induced a clear passive region on the polarization curves of AZ31 and shifted the breakdown potential over −1.0 V (Ag/AgCl), indicating the corrosion inhibition property of NaAlO2. In the polarization and EI tests, the aluminate ion loading did not noticeably enhance the corrosion protection ability of the LDH coating as shown by higher quasi-passive current density and lower R p than without loading. However, in the wet-dry corrosion tests, the LDHAlO2-coated AZ31 demonstrated less weight gain and fewer clusters of shallow micro-pits, while the LDHCO3-coated AZ31 showed numerous deeper pits on the entire surface. It was revealed that loading aluminate ions to the LDH coatings is promising for enhancing their corrosion protection ability in atmospheric environments.