Towards joinability of thermal self-piercing riveting for AA7075-T6 aluminum alloy sheets under quasi-static loading conditions

The self-piercing riveting (SPR) owns more advantages of acquiring high joint strength for similar and dissimilar metal sheets than the traditional spot welding. However, the conventional SPR may not obtain good joint quality for AA7075-T6 aluminum alloy sheets due to its high strength and low ductility. Thereby, the possibility of self-piercing riveting under elevated temperatures improving the riveting quality and mechanical behavior has thus been raised as an interesting topic. In this paper, a modified thermal self-piercing riveting (T-SPR) technology for AA7075-T6 sheets was proposed based on the process that the substrate was firstly heated and conducted by the subsequent riveting and heat treatment process. The post-riveted quality and quasi-static mechanical behavior of T-SPR joints under designated temperatures were intrinsically investigated by quantifying the interlocking parameters and the single-lap shear test to assess the optimized riveting temperature. Subsequently, an improved Arcan test was employed to investigate the quasi-static mechanical behavior of cruciform joints under different loading conditions. The failure modes of cross-lap joints were analyzed in detail by combining the experiments and FE simulations coupled with Johnson-Cook (J-C) strength and damage models. The influences of loading angle and loading speed on the mechanical behavior of T-SPR joints were further discussed. The outcomes show that the joinability of T-SPR for AA7075-T6 aluminum alloys can be largely improved by increasing the riveting temperature to 400°C. The loading angle and loading speed also have a significant impact on the mechanical behaviors and failure modes of T-SPR joints under quasi-static loading conditions.