The hybrid use of dissimilar lightweight materials, such as aluminum alloy and advanced high strength steel (AHSS), has become a critical approach to reduce the weight of ground transportation vehicles. Self-piercing riveting (SPR) as a preferred cold-forming fastening method is facing problems like weak interlocking and insufficient penetration, due to the reduced formability of AHSS. In this paper, a new process named electroplastic self-piercing riveting (EP-SPR) was proposed to reduce the deformation resistance of AHSS DP780, by applying a direct current (dc) to it during the riveting process. The influence of dc on force and displacement characteristics throughout the riveting process, joint physical attributes and quasi-static performances for two sheet combinations, e.g., AA6061-T6 to DP780 (combination 1) and DP780 to AA6061-T6 (combination 2), were studied and compared with the traditional SPR joints. The results showed that compared with the traditional SPR joints, the EP-SPR ones increased by 12.5% and 23.3% in tensile-shear strength and cross-tension strengths for combination 1, respectively. For combination 2, even though the EP-SPR joints decreased by 5.8% in tensile-shear strength, it could reduce the penetration risk of bottom AA6061-T6, and present a better energy absorption capability for the increased undercut amount. In addition, the corresponding cross-tension strength of EP-SPR joints still increases by 6.1%.
Keyhole refilled friction stir spot welding of aluminum alloy to advanced high strength steel