镀锌超高强钢/铝合金摩擦塞-铆复合点焊周向摩擦界面热-力行为控制机理

Spot welding of galvanized super-strength steel and high strength aluminum alloy is a key issue to manufacture lightweight automotive body with hybrid structures of steel/aluminum dissimilar metals. To solve this issue, a novel friction plug-rivet hybrid spot welding technology will be proposed in this project. By controlling thermal-mechanical behavior of circumferential direction friction interface between aluminum alloy and rivet, narrow processing window and low stability to realize metallurgical joining between aluminum alloy and rivet will be improved. On the basis of the influence of extrusion flow behavior of metals between the tip of the rivet and steel on flow behavior of aluminum alloy along the near field of circumferential direction of the rivet, plastic deformation behavior of the rivet and thermal effect of friction plug- rivet hybrid spot welding, a thermal-mechanical coupling finite element model will be established. And then, numerical simulation on friction plug-rivet hybrid spot welding will be performed, which will show the regularity controlling thermal-mechanical behavior of the circumferential direction friction interface between aluminum alloy and rivet. On the basis of physical simulation investigations of metallurgical joining mechanism at friction interface, thermal-mechanical conditions for metallurgical joining between aluminum alloy and rivet will be confirmed and its controlling mechanism will be clarified. Finally, the complete metallurgical joining at the whole interfaces between rivet and galvanized super-strength steel/aluminum alloy will be achieved. The friction plug-rivet hybrid spot welding technology in this project will offer technology support to manufacture lightweight automotive body with the hybrid structures of steel/aluminum dissimilar metals. The investigations on the metallurgical mechanism and its controlling of circumferential direction interface have theory and scientific significance.

镀锌超高强钢/高强铝合金的点焊是困扰钢/铝轻量化复合车身制造的主要问题之一。为此，本项目提出一种基于锥尖铆钉形貌的摩擦塞-铆复合点焊新技术，拟通过对其周向摩擦界面热-力行为的控制，解决铆钉/铝合金界面冶金连接工艺窗口窄、稳定性差等问题。本项目拟在探明铆钉锥尖与镀锌超高强钢间金属挤压流动行为对铆钉周向近域铝合金流动行为影响的基础上，结合铆钉塑性变形行为与摩擦塞-铆复合焊接热效应，建立点焊过程热-力耦合有限元模型，进行数值模拟研究，揭示铝合金/铆钉周向摩擦界面热-力行为控制规律；在此基础上，对铆钉/铝合金摩擦界面冶金连接机理进行物理模拟研究，确定实现铝合金/铆钉界面冶金连接的热-力条件，揭示其控制机理，实现铆钉与镀锌超高强钢/铝合金摩擦界面完全冶金连接。本项目提出的摩擦塞-铆复合焊接技术将为钢/铝轻量化复合车身制造提供技术支撑，对周向摩擦界面冶金连接控制机理的研究也具有较强的理论与学术价值。

为解决面向新能源汽车的超高强钢/铝合金轻量化复合车身结构的焊接问题，本项目提出一种集搅拌摩擦焊与铆接双重优势的绿色制造技术，即搅拌摩擦铆焊技术，又称摩擦塞-铆复合点焊技术。本项目开发了具有自主知识产权的摩擦塞-铆复合点焊装备，使用该装备实现了Q235低碳钢/7075高强铝合金、DP980超高强钢/7075高强铝合金的高质量摩擦塞-铆复合点焊。通过对两种金属组配的工艺研究，确定了最佳的工艺参数范围，接头的最高拉剪强度可达14.4kN，并呈韧性断裂。由于DP980钢的硬度要远高于Q235钢，这导致在摩擦塞铆复合点焊过程中铆钉的流动变形行为存在这明显的差别，导致了DP980钢与7075铝合金焊接过程中铆钉存在这一定程度的液化率铝合金渗透问题，对接头力学形成产生不利的影响；通过优化工艺参数可以显著抑制液化铝合金抑制问题。在此基础上，本项目对塞-铆复合点焊开展了数值模拟研究，建立了数值模拟有限元模型，并对DP980钢与7075铝合金摩擦塞-铆复合点焊焊接过程中铆钉变形行为与摩擦热效应进行了分析与研究，初步探明了摩擦塞-铆复合点焊的接头成形与连接机理。针对摩擦塞-铆复合点焊过程中铆钉周向界面与铝合金之间的界面反应的控制问题，本项目开发了一种摩擦界面热-力行为物理模拟的试验装置，实现了异种金属摩擦焊接过程中多参数的实时采集，利用该装置对钢与铝合金摩擦焊接过程中连接机理进行了的研究，揭示了钢/铝异种金属摩擦焊接过程热-力行为控制机理。建立了钢/铝异种金属摩擦塞铆复合点焊有限元模型，通过对焊接热过程的数值模拟，研究了摩擦塞-铆复合点焊周向界面的热-力行为，揭示了其调控机理，为钢/铝异种金属摩擦塞-铆复合点焊的应用奠定了理论基础。