面向难变形材料的机械-固相复合连接方法研究

The hybrid use of lightweight materials has already become the main trends to fabricate advanced lightweight auto-body. However, the usage of low ductility materials and its joining with dissimilar materials poses a big challenge to traditional resistance spot welding (RSW) process, which is one of the dominant joining methods in all-steel auto-body assembly.Nowadays, self-piercing riveting (SPR) and spot friction welding (SFW) are the most popular methods to join dissimilar materials. However, because the low ductility materials is brittle or too strong to deform, SPR method cannot get acceptable joint quality. SFW is another choice, but its strength cannot meet the requirements of auto-body desgn, for the residual process hole and severe tool wear in continuous working condition. In order to solve those challenges in dissimilar joining of low ductility materails with other materials, a novel joining process is proposed in this study, which combines the mechanical joining mechanism of SPR and the solid-state joining mechanism of SFW. In this novel process, the materials are softened by frictional heat generated by a high-speed rotating rivet to form a better mechanical connection, and via controlling frictional heat precisely, the solid-phase bonding will be formed among the interface of rivet and sheet metals. A prototype of mechanical/solid-phase hybrid joining process and a thermo-mechanical coupling FEA model will be established first. Based on the equipment and FE Model, the matching law and deformation mechanism of rivet and the low ductility materials under strong thermo-mechanical coupling condition will be studied; the control mechanism of frictional heat accumulation on the formation of the solid-phase connection, and the control mechanism of the mechanical/solid-phase hybrid connection on the joint properties will be explored too. Finally, a common mechanical/solid-phase hybrid joining method will be fromed through comprehensive process optimization, for joining typical less-deformable materials. Typical material combination, such as Al to Mg and Al to AHSS, will be selected to validate the proposed method in this study.

异种材料混用是汽车车身轻量化重要手段，传统电阻点焊工艺在异种材料连接时无法使用。目前异种材料连接主要采用自冲铆接和摩擦点焊，但对难变形材料，采用自冲铆接难以形成可靠接头，采用摩擦点焊则无法保证接头强度。项目提出一种机械-固相复合连接新方法，以自冲铆接机械连接为基础，引入摩擦点焊固相连接机制，通过铆钉高速旋转产生摩擦热软化金属，解决难变形材料机械连接时变形困难问题，实现难变形材料机械连接；通过摩擦热精确控制，实现铆钉与相邻材料的固相可靠连接，解决传统摩擦点焊残留工艺孔和搅拌针磨损问题。项目建立接头形成过程热力耦合模型，研究热力耦合条件下铆钉与难变形材料的匹配规律和变形机理；建立复合连接试验原型系统，探索摩擦热累积对接头固相连接控制机理；通过接头拉剪过程有限元仿真，揭示机械-固相复合对接头力学性能控制规律，形成难变形材料的机械-固相复合连接工艺，并应用于铝合金/镁合金、铝合金/高强钢的连接。

轻量化是汽车节能减排的重要手段，综合考虑减重效果和材料成本，多材料混用成为汽车车身制造技术发展的必然趋势。然而，异种材料的混用使得连接工艺面临巨大挑战。本项目针对异种难变形材料自冲铆接无法形成可靠接头，以及搅拌摩擦点焊接头强度低等问题，以自冲铆接机械连接为基础，引入搅拌摩擦点焊固相连接机制，提出一种机械-固相复合连接新方法，通过铆钉高速旋转产生摩擦热软化金属，解决难变形材料机械连接时变形困难及固相连接强度低等问题，实现难变形异种材料可靠连接。项目通过建立考虑大变形、材料失效的接头形成过程热力耦合模型，研究了关键工艺参数对接头内摩擦热演化和分布的影响规律，揭示了热力耦合条件下铆钉与难变形材料的相互作用机理；通过建立机械-固相复合连接试验原型系统，揭示了摩擦热累积和演化对接头固相连接行为控制机理，并提出了提升接头机械连接与固相连接性能的工艺优化方法；通过接头拉剪实验，揭示了机械-固相复合对接头力学性能控制规律，并应用于铝合金/镁合金的连接，使铝合金/镁合金的自冲摩擦铆焊接头与自冲铆接接头相比拉剪强度提升近1倍。项目研究成果为自冲摩擦铆焊技术在轻量化车身中的应用奠定了重要的理论和应用基础。.截至2016年底，本项目相关内容共发表SCI论文11篇，国内外会议论文5篇，其中邀请报告2次，申请国家发明专利2项，并研制自冲摩擦铆焊试验机1台。研究成果在汽车用异种材料连接领域产生了较好的学术影响，也引起了企业的高度关注，具有较强的产业化前景。.