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

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 in σ-FeZn10 layer due to the residual stress.Under tensile stress,the cracks propagate along the grain boundaries in σ-FeZn10 layer and then along the phase boundaries between the phases of FeZn13 and Zn in ζ-FeZn13 layer,finally along the grain boundaries in η-Zn layer until the coating exhibits fracture.