Influence of process parameters and heat treatment on self-piercing riveting of high-strength steel and die-casting aluminium

The application of steel/die-casting aluminum alloy is an inevitable trend in the development of automotive lightweight technology. The joining process of self-piercing riveting (SPR) is the key technology to guarantee the collision safety for the body. However, the crackings on joint button can be easily found owing to the low ductility of die-casting aluminum. This paper aims to investigate cracking mechanism and improve the SPR joinability by exploring methods of cracking inhibition. Parametric study is performed to explore the effects of heat treatment, process parameters on crack inhibition and forming quality of SPR with steel/die aluminum alloy. The results show that SPR joinability can be improved by larger elongation and lower yield strength by proper heat treatments, i.e., AlSi10MnMg-T6 and AlSi10MnMg-T7. Meanwhile, the depth and diameter of the die are the main factors affecting cracking generation and forming quality. Similar to the upsetting process, tangential tensile stress is generated on the bottom surface in the riveting process, it leads to cracking generation on the bottom surface. This paper further studies the effects of heat treatment and stack direction on joint quality and mechanical response of SPR joints. Tearing failure of the lower sheet is the main factor causing failure of steel-aluminium joint (steel is the top sheet). The heat treatment mainly affects the energy absorption value and has a relatively small effect on the peak force. The mechanical properties of the steel-aluminium joints are superior to those of aluminium-steel joints (aluminium is the top sheet).