Influence of Al Contents on Corrosion Performance of Hot-dip Zinc Alloys

The microstructure and corrosion performance of Zn-4Al, Zn-5Al and Zn-6Al galvanized alloys were analyzed by optical microscopy, electrochemical tests, scanning electron microscopy and so on. The results show that the microstructure of Zn-4Al alloy was composed of lamellar Zn-Al eutectic and lots of primary β-Zn phase. The microstructure of Zn-5Al alloy was Zn-Al eutectic and a little primary β-Zn phase. Besides Zn-Al eutectic, a few massive α-Al primary phase was discovered in Zn-6Al alloy, and the Zn-Al eutectic around primary α-Al phase was mostly granular. The electrochemical tests show that the corrosion current density Jcorr of Zn-5Al alloy was the least, and the electrode polarization resistance Rp of Zn-5Al alloy was the largest, so the corrosion performance of Zn-5Al alloy was the best. The corrosion of Zn-4Al and Zn-5Al alloy occurred preferentially at the primary β-Zn phase, and the corrosion of Zn-6Al alloy occurred preferentially at Zn-Al eutectic around primary α-Al phase.