Effects of Al contents on microstructure and properties of hot-dip Zn-Al alloy coatings on hydrogen reduced hot-rolled steel without acid pickling

A new hot-dip galvanizing method was employed on hot-rolled low carbon steel.The effects of Al contents on microstructure,micro-hardness and corrosion resistance of Zn-Al alloy coatings were systematically investigated.Phase composition,microstructure and element distribution in Zn-Al alloy coatings were analyzed using X-ray diffraction(XRD)and electron probe micro analysis(EPMA),respectively.It is found that Al content(0.6-6.0 wt.%)in galvanizing zinc affects surface quality and adhesion between coatings and matrix in the newly developed method.In addition,with increasing Al content,micro-hardness significantly increased due to the increase in Zn-Al eutectoid phases.Potentiodynamic polarization and electrochemical impedance spectroscopy(EIS)also revealed that increase in Al plays a noticeable role in improving the corrosion resistance of Zn-Al alloy coatings.