铝合金压印-点焊复合连接工艺及其接头强韧化研究

In order to deal with the difficulties incurred by the defect and strength loss of automotive-manufacturing aluminum alloys joints during the assembling process, hybrid resistance spot clinching method is raised by this proposal, which can produce the Al-alloys joints having both mechanical interlock and metallurgical bonding effects. The research is implemented regarding following three aspects: (1) The hybrid joining process can be realized within one step by exerting the electro-plastic effect, which involves pressing and charging simultaneously for a local site; By combining both the multi-physics coupled finite element and CALPHAD technique, the prototype and processing parameters can be optimized. (2) Data of the heat and mass transfer in macro scale can be transfer into the microstructure evolution predicting by establishing a mesoscopic volume element. The strength and toughness of the resistance spot clinching joints can be predicted by this model. According to corresponding criterion, the filler metal can be optimized. Based on the former two points, the mechanical behaviors of the resistance spot clinching joints are studied. Due to its special load-bearing structure, the local stiffness shall be established to predict its peak loading ability; With the research progressing, corresponding model and criterion can be established while the parameters can be optimized. This is of significant help to promoting the development of novel joining method which is designed for new generation of materials for vehicle mass reduction.

为突破车用铝合金连接工序中由工艺缺陷及强度损失造成的技术瓶颈，本项目率先提出压印-点焊复合连接方法，制备机械自锁-冶金键合双重连接效应的铝合金接头。本项目在以下三个层次开展研究：（1）应用电致塑性效应，同时对工件被连接区域进行加压与通电，实现一步法复合连接工艺；通过多场耦合有限元结合相图计算技术的手段，迭代优化原理样机及工艺过程设计。（2）通过建立介观体积单元将宏观传热传质数据与微观组织演化过程进行联系，分析复合型接头的强度、韧性演化规律；根据相关判据，优化填充材料选型。（3）在前两项研究内容的基础上，针对复合接头特有的承载结构的力学行为开展研究，建立局部刚度参量，提供峰值载荷预测方案。通过项目研究建立相关模型与判据，对工艺参数进行优选，推进面向车身轻量化材料的新型连接工艺的发展。

为突破车用铝合金连接工序中由工艺缺陷及强度损失造成的技术瓶颈，本项目提出一种新型的压印-点焊复合连接方法，制备机械自锁-冶金键合双重连接效应的铝合金接头。按照预定研究计划，本项目完成以下三方面主要研究内容：（1）压印-点焊复合连接工艺研究：通过改装逆变直流伺服电机加压式电阻点焊设备实现了压印-点焊复合连接工艺。基于多元数理统计方法，开展了多种加工参数（包含模具形状、加压力度、电流幅值、通电时间、热补偿带选材等）的优化研究。（2）压印-点焊复合连接过程微观组织演化研究：基于多元热动力学相图计算技术，建立介观解析体积单元，对铝合金半固态加工区间进行固相百分数、合金元素的再分配以及微区热物理属性计算，与多物理场耦合有限元模型相结合，精确求解连接过程的传热传质及液固相变过程的关键参数的演变规律。研究结果表明，熔化区中合金元素会偏聚于晶界处，使有效溶质含量降低，弱化接头的烘烤强化性能。采用较高合金元素含量水平的填料铆钉，可以抑制元素偏析带来的接头弱化效应。（3）复合接头承力结构研究：基于数字图像相关法测试技术，提取了接头在承受拉剪载荷时的全场应变数据。通过建立局部刚度参量，综合分析了复合接头具备的机械自锁-冶金键合双重连接效应，揭示其可承受高外部载荷的力学机理。研究结果表明，压印-点焊复合连接接头既保障连接区的局部强度处于较高水平，又通过结构效应提高了局部刚度，因此其力学性能显著优于电阻点焊接头。