Effect of Mg Addition on Microstructure and Sacrificial Anode Protection Performance of Hot Dip Al-5Zn-4Si-xMg Coating

The effect of Mg addition on the microstructure and sacrificial anode protection performance of a hot-dip Al-5Zn-4Si-xMg coating was studied by scanning electron microscopy (SEM-EDS), an X-ray diffractometer, and an electrochemical workstation. The results showed that Al-Zn-Si alloy was composed of an Al-rich phase and a Zn-rich phase. The MgZn2 phase appears after Mg addition. When the addition of Mg increased to 0.15 wt.%, the Mg2Si phase began to appear in the alloy. The hot-dip Al-5Zn-4Si-xMg coating consisted of Si particles, an Al-rich phase and a Zn-rich phase. When the Mg content increased to 0.15 wt.%, the Mg2Si phase and Al + Zn + MgZn2 eutectoid phase began to appear in the coating. In the full immersion corrosion test of the hot-dip Al-5Zn-4Si-xMg coating, the order of corrosion resistance was 0.15% Mg coating > 0.2% Mg coating > 0.05% Mg coating > 0 Mg coating. In the corrosion process of the hot-dip Al-5Zn-4Si-0.15Mg coating, with the increase in immersion, the self-corrosion current of the coating decreased, and the sacrificial protection performance was the best.