基于环形聚流效应的铝/钢电阻点焊界面反应及金属间化合物生长机制

In automotive industry, reducing the weight of automobile body is inevitable as protecting environment and energy saving get more serious. Against the background, aluminum-steel hybrid structural automobile body is an expected structure for the weight reduction. Hence it is necessary and urgent to study reliable technology and related mechanism for the joining of aluminum/steel. With interfacial intermetallic compounds growth mechanism as the research object, controlling temperature field as clues in this project, composite and embedded electrodes will be used to weld aluminum alloy and steel in order to make welding zone current gather in ring shape, thereby the temperature field is concaved during resistance spot welding. On the basis of clarifying the essential relationship between welding zone temperature field and ring-gathered current, intermetallic compounds evolution rule and reaction behavior of Al and Fe atoms at the welding interface will be explored. The influence of ring-gathered current on the structure, morphology, thickness and distribution of the intermetallic compound will be detailedly analysed. Based on these investigations, the growth mechanism of intermetallic compounds at the welding interface will be illustrated. From the design of electrode structure and welding parameters, an effective strategy, by which interfacial intermetallic compounds growth can be controlled and the joint performance can be improved, will be put forward. The expected results can provide a theory basis for the process design of resistance spot welding of dissimilar metals with the larger disparity in thermal and physical properties. Meanwhile, a technical support can be obtained for the engineering application of aluminum-steel hybrid structure automobile body.

随着环保、能源问题的日益突出，汽车车身轻量化已成为汽车工业发展的必然选择，而“钢+铝”复合结构车身有望随之成为轻质汽车的主流结构。因此，开展铝/钢异种金属可靠连接技术及相关机理的研究日趋迫切。本项目以界面金属间化合物生长机制为研究对象，以控制温度场为线索，利用研制的嵌入式复合电极点焊铝/钢异种金属，使焊接区电流在点焊过程中发生环形聚集而凹化温度场。在探明焊接区温度场与环形聚流间内在关系的基础上，探索Al、Fe等元素间界面反应行为及金属间化合物的演变规律，分析环形聚流效应对界面的金属间化合物层的结构、形貌、厚度及分布等特征参量的影响，进而阐明界面金属间化合物的生长机制，以期从电极结构、工艺参量的设计出发提出有效控制界面金属间化合物生长进而提高接头性能的策略。本项目预期研究成果能为热物性悬殊的异种金属电阻点焊工艺设计提供理论依据，为“钢+铝”复合结构轻质车身的工程化应用提供技术支撑。

随着环保、能源问题的日益突出，汽车车身轻量化已成为汽车工业发展的必然选择，而“钢+铝”复合结构车身有望随之成为轻质汽车的主流结构。因此，开展铝/钢异种金属可靠连接技术及相关机理的研究是非常必要的。研究了焊接参数对接头性能的影响，分析了接合界面金属间化合物的结构、形貌、厚度及分布等特征参量，探讨了界面金属间化合物的生长机制，并探索了界面金属间化合物对接头性能的影响。基于环形聚流效应的铝合金/低碳钢点焊，在所选参数范围内接头熔核直径随焊接电流、焊接时间、电极压力的增大而增大，而接头抗剪力则随焊接电流、电极压力的增大而增大，随焊接时间的增大呈线增大后下降的趋势。获得接头的最大抗剪力为6.39 kN，相比采用普通球面电极点焊，接头的抗剪载荷提高了28.6%。基于环形聚流效应的铝合金/低碳钢点焊接头界面的反应物与与常规点焊基本相同，主要由Fe2Al5和FeAl3构成，但反应层厚度分布得到了改善。焊点中心部位反应层生长得到抑制，最厚仅为2.5μm。FeAl3的生成归结于其生成自由能较低，而Fe2Al5的生长主要因其结构上在C轴方向存有大量Al原子空位而造成的各向异性扩散。接头断口分析及原位抗剪试验结果显示：铝合金/低碳钢点焊时，将界面反应层厚度控制于2μm以下时，接头性能良好，反应层对接头性能影响较小。另外，本研究还研发出一种适于铝合金/钢焊接的名为电阻铆焊的新颖方法。本项目所得研究成果为热物性悬殊的异种金属电阻点焊工艺设计提供理论依据，为“钢+铝”复合结构轻质车身的工程化应用提供技术支撑。