铜/镀镍钢微电阻点焊接头形成机理

采用微电阻点焊对纯铜和镀镍钢片异种金属进行了点焊连接,通过拉剪试验、光学显微镜、扫描电镜和能谱分析,研究了镀层金属镍在铜/镀镍钢片微电阻点焊冶金过程中对接头形成和接头强度的影响. 结果表明,铜/镀镍钢片微电阻点焊接头的形成机理包括固相连接和熔化连接,其形成过程为: 铜和镀层镍在锻压力和析出热量下,形成固相连接;在铁和镀层镍之间开始熔化;镀层镍被熔化的金属向边缘处挤压,镍在边缘处与铁、铜形成了新的组织;熔核的形成. 在两种不同的接头形成机理下,其拉伸断口都有呈抛物线状或拉长的韧窝出现.

Formation mechanism of copper/nickel-coated steel dissimilar metals joint by micro spot resistance welding

Dissimilar metals of pure copper and nickel-coated steel were joined by micro spot resistance welding. Tensile shear test, optical microscopy (OM), scan electron microscopy (SEM) and energy spectrum analysis (EDS) were used to study the influence of coated metal Ni on formation and shear strength of the joint. The results show that formation mechanism of copper/nickel-coated steel dissimilar metals joint included solid state bonding and fusion bonding. In formation of joint, Cu and coated metal Ni bonded at solid state under the forging force and welding heat. The coated metal Ni and Fe began to melt. Then coated metal Ni was extruded to the edge by the melted metal. New structure formed between Ni, Fe and Cu at the edge. Finally, the nugget formed. Parabolic and elongated dimples were observed at the fracture surface in both joints under two different mechanisms.