电极形状对铝-钢点焊接头组织及力学性能的影响*

研究6061-T6铝合金-SUS301L不锈钢异种金属电阻点焊接头的微观组织特点及电极形状的影响规律。结果表明，铝-钢点焊接头具有熔-钎焊特征，铝合金熔核由α-Al胞状晶、胞状树枝晶和树枝晶组成，铝/钢界面层具有双层结构，靠近铝熔核侧主要为细针状Fe₄Al₁₃，靠近不锈钢侧主要为Fe₂Al₅金属间化合物，接头主要为界面断裂模式，铝/钢界面是点焊接头最薄弱的区域。电极形状对铝合金-不锈钢点焊接头具有明显的影响。获得的优化电极形状为：不锈钢侧为圆形平面电极，电极端面直径为10 mm;铝合金侧为球面电极，球面半径为35 mm。在优化电极条件下，铝合金-不锈钢点焊接头的熔核直径、拉剪力及压痕率分别为7.5 mm、4.7 kN和13.5%。与采用F型电极相比，其熔核直径和拉剪力分别提高53.1%和56.7%，压痕率降低47.3%。因此，采用优化电极更有利于改善铝合金-不锈钢电阻点焊接头的力学性能及表面质量。

Effects of Electrode Morphology on Microstructures and Mechanical Properties of Spot Welded Al-steel Joints

Microstructural characteristics of dissimilar resistance spot welded joints of 6061-T6 aluminium alloy and SUS301L stainless steel,and effects of electrode morphology are studied.Results indicate that spot welded aluminium-steel joints have welding-brazing characteristics.The aluminium nugget consists mainly of the cellular crystal,cellular dendrites and dendrites.The aluminium/steel interface zone has a double layer structures:The needle-like Fe4Al13 layer at aluminum side and the Fe2Al5 intermetallic compound (IMCs) at steel side,and it is the weakest zone of the joints.The electrode morphology has great effects on spot welded joints of aluminium alloy and stainless steel.The optimised electrodes are a planar circular tip electrode with tip diameter of 10 mm on the stainless steel side and a spherical tip electrode with spherical radius of 35 mm on the aluminium alloy side.When the optimised electrodes are used,the nugget diameter,tensile shear load and indentation ratio of spot welded joint are 7.5 mm,4.7 kN and 13.5％,respectively.The nugget diameter and joint tensile shear load increases by 53.1％ and 56.7％ respectively,and the indentation ratio decreases by 47.3％ compared with F-type electrodes.Therefore,it is more favorable to use the optimized electrodes for improving the mechanical properties and appearance quality of spot welded joints of aluminum alloy and stainless steel.