Electrochemical studies on ammonium magnesium carbonate tetrahydrate/calcium carbonate composite coating on AZ91D magnesium alloy

At present, it is still a challenge to efficiently and environmentally prepare corrosion-resistant coating with good adhesion on magnesium alloy. In this paper, the composite coating of ammonium magnesium carbonate tetra -hydrate (AMCT) and calcium carbonate (CC) was prepared on AZ91D magnesium alloy by a simple one-step in -situ growth process. The surface morphology and composition of the samples were characterized. The corrosion resistance of the sample in 3.5 wt%NaCl solution was evaluated, and the electrochemical test results showed that the Icorr of the coated samples decreased by 3 orders of magnitude compared with that of the Mg substrate, and the corrosion resistance was significantly improved. In addition, the forming mechanism and adhesion properties of the coating are also discussed. The results show that the ratio of AC/CG in the reaction solution and the re-action time are important factors to determine the coating formation. When the molar ratio of AC/CG is 5:1 and the reaction time is 89 h, the prepared coating has good adhesion to the substrate and the best corrosion resistance. The method does not use expensive drugs and instruments, and does not need complicated pre-treatment, so it has great advantages in reducing cost and improving efficiency.

Automated summary

This study presents a simple one-step in-situ growth process for preparing a composite coating of ammonium magnesium carbonate tetra-hydrate (AMCT) and calcium carbonate (CC) on AZ91D magnesium alloy. The coated samples exhibited good adhesion and significantly improved corrosion resistance in 3.5 wt% NaCl solution. The molar ratio of AC/CG and the reaction time were found to be crucial factors determining the coating formation.