钢板表面热浸镀锌层的拉伸断裂机理

Tensile Fracture Mechanism of Hot Dip Zn Coating on Steel Plate Surface

采用热浸镀技术在Q235钢板表面制备了镀锌层,研究了浸镀时间对镀锌钢板拉伸性能的影响,通过扫描电镜观察了拉伸断裂后镀层表面、截面和断口处的形貌,分析了镀层的断裂机理。结果表明:与基体相比,Q235钢板热浸镀锌后的抗拉强度和塑性变形能力均下降;镀件抗拉强度的下降是由表面镀锌层强度低于基体的强度造成的;而塑性的下降则是由热浸镀时在基体表面形成的微裂纹造成的;由于残余应力的存在,微裂纹首先在σ-FeZn10层中形成,在受到拉应力时,裂纹沿晶界在σ-FeZn10层中向上扩展,然后在ζ-FeZn13层中裂纹沿着FeZn13/Zn的相界面扩展,最后在η-Zn层沿晶界扩展直至镀层发生完全断裂。

The Zn coating was prepared on the surface of Q235 steel plates by hot dipping,and the effect of dipping time on the tensile behavior of Zn coated steel plates was studied.The Surface,cross-section and fracture microstructure of the Zn coating after tensile fracture were characterized through scanning electron microscopy(SEM),and the fracture mechanism of the Zn coating was analyzed.The results show that the tensile strength and plasticity of the Zn coated Q235 steel plates decrease in comparison to the substrate.The decline of tensile strength is because that the strength of the Zn coating is less than that of the substrate.The micro-cracks in the substrate in dipping can be used to explain the decline of the plasticity.The micro-cracks first occurs inσ-FeZn10 layer due to the residual stress.Under tensile stress,the cracks propagate along the grain boundaries inσ-FeZn10 layer and then along the phase boundaries between the phases of FeZn13 and Zn inζ-FeZn13 layer,finally along the grain boundaries inη-Zn layer until the coating exhibits fracture.