Study Of The Interface Reaction During Hot-dip Zn-Al Alloy By Solvent Method

Hot dip galvanizing technology is a kind of protection method with low cost and excellent corrosion resistance.The corrosion resistance of hot dip galvanized coatings depends on the composition of the interfacial layer,the microstructure and the hot-dip alloy.In the hot-dip galvanized Zn-Al alloy coating,the interfacial layer composition is Fe-Al intermetallic compound.It is important to study the characteristics of its interfacial layer formation to further improve its performance.In this paper,hot-dip Zn-Al alloy coating was prepared by using Q235 steel as the substrate in the temperature range of 430?⁵30?.Scanning electron microscopy?SEM?and X-ray diffraction?XRD?were used to investigate the effects of hot-dip temperature and Al content on the phase composition and microstructure of the interfacial layer.The influence of the test temperature and the Al content in the zinc bath on the wettability of the Zn-Al alloy and the steel substrate was studied by using the high temperature wetting property measurement system.Results showed that the wettability of Zn-Al alloy and steel matrix is not related to the experimental temperature,but to the alloy composition.With the increasing of Al content,the initial wetting angle of Zn-Al alloy and steel matrix increases gradually,and the wetting rate gradually decreases.With the increasing of temperature,the initial wetting angle of Zn-Al alloy and steel matrix changes little,but the wetting speed is gradually accelerated.The microstructure of the interfacial layer of Zn-Al alloy is mainly divided into two types:lamellar structure and ellipsoidal structure.The flaky structure is FeAl₃ phase,and the ellipsoidal structure is Fe₂Al₅ phase.The FeAl₃ phase is preferentially formed by the interfacial reaction of Zn-Al alloy,and then the FeAl₃ phase is gradually transformed into Fe₂Al₅ phase.The higher the Al content in the zinc bath,the longer the presence of the FeAl₃ phase in the interfacial layer.When the Al content in the zinc bath is low?less than 1%?,the thickness of the interfacial layer does not change obviously with the change of the temperature,the variation range is about 0.8³?m.When the Al content is 5%?Galfan?in the zinc bath,the change of the thickness of the interface layer of hot-dip plating Galfan alloy with temperature is y₁=0.05T-32 with the hot-dip plating temperature of 430?⁴90?.When the hot-dip plating temperature is 490?⁵30?,the thickness of the interface layer of hot-dip Galfan alloy varies with temperature y₂=1.02T-497.When the temperature is low,the thickness of the interfacial layer has no significant difference with the increase of Al content in the zinc bath.When the temperature is high,the thickness of the interfacial layer increases with the increase of the Al content in the zinc bath.Indicating that in the high temperature stage,the main factors affecting the growth of the interface layer are Al content.