Study on the microstructure and corrosion resistance of Zn-3Al-xMg alloy

Low-aluminium Zn-Al-Mg alloys (Al content is 1-3 %) were expected to be widely used in automotive panels due to their good coating properties and surface quality. However, the effect of Mg on the microstructure and corrosion resistance of Zn-Al-Mg alloys has not been studied thoroughly enough. In order to investigate the corrosion resistance law of Mg on Zn-3Al alloys. The microstructure and corrosion resistance of Zn-3Al-xMg (x = 0.5, 1, 2, 3 wt%) alloys were investigated in the present work. The ternary eutectic (Zn/Al/MgZn2) in the microstructure increased, and the Al-rich phase disappeared with increasing Mg. The grains were also refined. The maximum ratio of ternary eutectic in the alloy was achieved by controlling the Mg content, contributing to the most favourable corrosion resistance. The electrochemical and corrosion behaviour analysis indicated that the Zn-3Al-2Mg alloy exhibited superior corrosion resistance due to the lower presence of Al-rich phases and a larger ternary eutectic area. However, the ternary eutectic in the alloy was completely transformed into Zn/Al/ Mg2Zn11 when the Mg was 3 %, leading to decreased corrosion resistance. The corrosion resistance mechanisms of Zn-3Al-xMg were analyzed and discussed by studying the microstructure changes, electrochemical analysis, corrosion morphology, and products of the Zn-3Al-xMg alloy.