Effects of Al and RE on microstructure and corrosion resistance of Zn-Al alloy coatings

The hot-dip galvanizing alloys of Zn-(0.02-5)%Al and Zn-5%Al-0.05%RE(mass fraction) were obtained on the surface of Q235 steel by solvent drying method. The macroscopic morphology, the surface and section microstructures of the alloy coatings were observed by optical microscopy and SEM. The element distribution in the alloy coatings was analyzed by energy disperse spectroscopy, and the corrosion resistance of the alloy coatings was investigated by the neutral salt spray test and full immersion corrosion, respectively. The results show that the coating lightness is excellent when the Al content is 0.02%(mass fraction), and the coating lightness declines with increasing the Al content. The Zn content reduces and the Fe and Al contents increase gradually in the outer η phase and T phase close to the steel substrate. The corrosion rate of the hot-dip galvanizing Zn-Al alloy coating decreases with increasing the Al content in Zn-Al alloy bath. The corrosion resistance can be enhanced with the addition of rare earth elements in the Zn-Al alloy bath.