铜/镀镍钢薄片微电阻点焊接头组织性能研究

Study on Microstructure and Mechanical Properties of Micro-resistance Spot Welding Joint of Copper and Nickel-plated Steel Sheet

采用微电阻点焊实现了0.2mm厚的铜薄片和0.3 mm厚的镀镍钢片的连接,使用光学显微镜、SEM、EDS等方法对接头组织性能进行了研究。结果表明,焊接电流为2.3 kA时,接头处无法形成一个整体熔核,在镀镍钢和铜薄片界面出现少量“月牙”型组织;焊接电流增大到2.9 kA时,在镀镍钢熔核区的两端出现“漩涡”状组织,在焊核中心镀镍钢与铜交界处出现“钳子”结构,“钳子”结构外层存在镀层镍;焊接电流为3.5 kA时,形成了倒三角形的熔核,熔核中心可见明显的“漩涡”状组织。接头抗拉剪力随焊接电流增加而增加,焊接电流为3.5 kA时接头抗拉剪力最大。熔核处显微硬度最大,镀镍钢片热影响区的显微硬度约250 HV左右,而形成熔核时由于析出热量过大导致铜侧热影响区晶粒粗大,硬度降低,硬度仅在75HV左右。

The 0.2 mm thick copper sheet and 0.3 mm thick nickel-plated steel sheet were jointed by micro-resistance spot welding. The microstructure and mechanical properties of welded joints were studied by using optical microscopy, SEM, EDS and other methods. The results show that when the welding current is 2.3 kA, an integral nugget can not be formed at the joint, a few crescent microstructures can be found at the interface of nickel-plated steel sheet and copper sheet. When the welding current is 2.9 kA, a vortex structure is found at both ends of the weld nugget zone, a clamp structure is found at the interface of nickel-plated steel sheet and copper sheet in the nugget center and it exists nickel at the outside of clamp structure. When the welding current is 3.5 kA, inverted triangular nugget is formed, and an obvious vortex structure is found in the nugget center. The tensile shear strength increases with the increase of welding current. When the welding current is 3.5 kA, the tensile shear strength is the maximum. The microhardness of the nugget is the maximum, the microhardness of the heat affected zone at the side of nickel-plated steel sheet is about 250 HV. Because of the excessive heat release during the formation of weld nugget, the grain of the heat affected zone at the copper side is coarse, and the hardness decreases, which is only about 75 HV.