锌铝镁镀层在加热过程中的组织和耐蚀性

Microstructure evolution and corrosion resistance of ZnAlMg coating during heat treatment

锌铝镁镀层相对于纯锌镀层具有更好的耐蚀性,结合其特有的划伤自愈、切口保护等特点受到越来越多的钢铁生产企业及下游用户的重视,尤其在材料服役条件较为严苛的环境,客户采用该新型镀层的愿望较为强烈。锌铝镁镀层钢板在使用过程中会遇到热加工和热处理,最常见的是焊接和切割。因此研究锌铝镁镀层在不同温度区间的性能稳定性越来越受到关注。为了探究锌铝镁镀层在温度变化过程中组织和性能的变化,更好地提高镀层耐热性能,研究了不同铝含量的锌铝镁镀层(Zn1Al1Mg、Zn55Al1Mg)在不同的加温温度(300、500、700℃)进行加热,并随炉保温10 min之后镀层内部的组织变化以及对物理和化学性能产出的影响。通过相图计算预测了保温之前镀层的析出相,通过电镜表征热处理后镀层的截面组织和表面组织的形貌,对各个不同的区域进行电镜自带的EDS的成分检测;同时,对镀层中不同相的组成进行了XRD的测试;对不同热处理工艺的试样进行维氏硬度的测试;对试样的耐腐蚀性能用电化学的方法来评估。结果表明,在加热到700℃的时候,Zn1Al1Mg和Zn55Al1Mg镀层的表面组织和截面组织的形貌都出现了很大的变化,对于Zn1Al1Mg镀层组织明显的分为2层,分别为Zn-Fe层和Fe-Zn层;对于Zn55Al1Mg的镀层组织,产生了从基体生长的柱状富铝相,在钢板和镀层的交界处密集生长;表面组织出现了疏松多孔的组织;电化学的结果显示,2种镀层的耐腐蚀性能都有所下降。维氏硬度的检测表明,2种镀层经过热处理后硬度都得到了提高。

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 welding and cutting process.Therefore,the study of the performance stability of Zn-Al-Mg coatings in different temperature 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 furnace 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 different 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.