低合金高强度角钢热镀锌层局部结合力差异原因分析

Analysis on Local Adhesion Differences of Hot Dip Galvanized Coating on Low-Alloy High-Strength Angle Steel

利用扫描电镜(SEM)、光学显微镜(OM)等手段分析了高强度角钢热镀锌层局部产生结合力差异的原因,比较了镀层结合力好的部位和结合力差的部位的镀层组织及钢基体组织的微观组织。研究结果表明:(1)角钢热镀锌层出现结合力差异的原因与镀层组织有关。结合力好区域的镀层组织由小柱状或小块状ζ层和不连续锯齿状δ层构成。锤击处整体以凹坑形式存在,合金层被挤压变形但未出现裂纹;结合力差区域的镀层组织由较粗大柱状或大块状的ζ层和连续且厚的δ层构成;锤击处镀层从基体界面处剥离;(2)钢铁基材的表面组织状态对热镀锌组织产生影响。热镀锌过程中,近平衡组织有利于铁的扩散,促进ζ相生长,抑制δ相生长,有利于热镀锌层结合力;非平衡组织的出现,因其固溶强化,晶格畸变、内应力等原因,会在一定程度上影响铁的扩散,抑制ζ相生长,促进δ相生长,不利于热镀锌层的结合力。

The reasons for the local adhesion differences of the hot-dip galvanized coating on high-strength angle steel were analyzed by means of scanning electron microscopy(SEM)and optical microscopy(OM),and the microstructures of the coating and steel base in the good bonding area and poor bonding area of galvanized angle steel were compared.Results showed that:(1)The adhesion difference of the coating on steel substrate were closely related to the microstructure of the caoting.The coating area with good bonding strength was characterized with small column-like or lumpyζphase and discontinuousδphase.When the coating suffering hammering,the hammered area was generally in the form of pits,and the alloy layer was extruded and deformed without cracks.The coating area with poor bonding strength consisted of a coarse columnar or bulkyζphase and a continuous and thickδlayer,which would be stripped from the substrate interface when the coating suffering hammering.(2)Moreover,the surface microstructure of steel substrate had influence on the galvanized coating.During galvanizing,equilibrium structure was in favor of the diffusion of Fe,facilitating the growth ofζand limiting the growth ofδ,which was beneficial to the bonding between coating and substrate.However,the appearance of non-equilibrium structure could inhibit the diffusion of Fe,lower the growth ofζand benefit to the growth ofδbecause of the solution strengthening,lattice distortion and internal residual stress,which was harmful for the bonding strength of hot-dip galvanized coating.