Process development for mechanical joining of 7xxx series aluminum alloys

Mechanical joining technologies like self-pierce riveting with semi-tubular (SPR-ST) and solid rivets (SPR-S) are standard joining techniques for processing 5xxx and 6xxx series aluminium alloys in automotive industry. Due to the lower ductility and the vulnerability regarding stress corrosion cracking of 7xxx series aluminum alloys the conventional self-pierce riveting process can't be used for joining these materials. Due to the very good strength properties and the, compared to steel, lower density 7xxx series aluminum alloys are becoming more relevant as material for structure parts in car body construction. In aircraft construction, these alloys are used for decades. However, the higher requirements in automotive industry regarding automation other technologies for processing these high- and ultra high-strength aluminum alloys must be found. Currently. This presentation shows an numerical and experimental analysis of the different problems occurring during or after the conventional mechanical joining of the high strength aluminum alloys of the 7xxx series (EN AW-7021 T4, EN AW-7075 T6). Furthermore this presentation describes different pre-process methods by which the fracture in the high strength aluminum, caused by the mechanical joining process, can be prevented and proper joining results are achieved. On this basis, the different approaches are compared regarding process time and joint strength.