A hot-dip self-passive zinc alloy coating to inhibit the galvanic corrosion of a Mg alloy

Galvanic corrosion is one of the most critical issues currently hindering the industrial applications of magnesium (Mg) alloys. In this study, to solve this problem effectively, durably, and economically, a 30-second 360°C rapid hot-dipping technique was developed to convert the surface of Mg alloy WE43 into a metallurgically bonded over 1 mm thick uniform Zn-alloy coating. The alloyed surface layer was characterized and evaluated using microscopic and electrochemical techniques. The results demonstrated that this surface coating had a multilayered microstructure and could self-passivate in 3.5 wt% NaCl. The self-corrosion current density of the Zn-alloyed surface was in the order of 10⁻⁶ A/cm², and the galvanic current density stably remained below 20 × 10⁻⁶ A/cm² when the surface-alloyed Mg alloy was coupled with pure Al or galvanized Q235 steel in the 3.5 wt% NaCl. The Zn-alloyed surface of the Mg alloy could even self-heal in case its surface was scratched. Based on the microstructural and electrochemical characteristics, the surface alloying mechanism on the WE43 is analyzed, and the underlying reasons for the outstanding galvanic corrosion resistance of the Zn-alloyed surface are elucidated.