Microstructure evolution and corrosion resistance of ZnAlMg coating during heat treatment
Zn-Al-Mg coating has better corrosion resistance compared to pure zinc coating.Combined with its unique characteristics of scratch self-healing and incision protection,it has attracted more and more attention from steel production enterprises and downstream users,especially in environments with strict material service conditions.Zn-Al-Mg coated steel plates will encounter heat processing and heat treatment during use,most commonly in weld-ing and cutting process.Therefore,the study of the performance stability of Zn-Al-Mg coatings in different tempera-ture ranges is receiving increasing attention.In order to explore the changes in microstructure and properties of Zn-Al-Mg coatings during temperature changes,and to better improve the heat resistance of the coatings,the internal structural changes of Zn-Al-Mg coatings(Zn1Al1Mg,Zn55Al1Mg)with different Al contents heated at different heating temperatures(300,500,700 ℃)and their effects on physical and chemical properties after ten minutes of fur-nace insulation is investigated.The precipitation phase of the coating before insulation was predicted through phase diagram calculation.The cross-sectional structure and surface morphology of the heat-treated coating are mainly characterized by electron microscopy,and the composition of EDS inherent in electron microscopy is detected in dif-ferent areas.Meanwhile,XRD tests were conducted on the composition of different phases in the coating.Perform Vickers hardness testing on samples from different heat treatment processes.Evaluate the corrosion resistance of the sample using electrochemical methods.The results showed that when heated to 700 ℃,there were significant changes in the morphology of the cross-sectional structures and surface structuers of Zn1Al1Mg and Zn55Al1Mg coatings.The structure of the Zn1Al1Mg coating is clearly divided into two layers,namely the Zn-Fe layer and the Fe-Zn layer.For the coating structure of Zn55Al1Mg,columnar aluminum rich phases grow from the substrate,densely growing at the junction of the steel plate and coating.And a loose and porous surface structure appeared.The electrochemical results show that the corrosion resistance has decreased.The Vickers hardness test shows that the hardness of the coating has been improved after heat treatment.
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