Effects of Laser-Assisted Thermal Treatment on Self-Piercing Riveting (SPR) of DP 1180 and CFRP

This study investigated laser-assisted thermal treatment to enhance the self-piercing riveting (SPR) joint quality for dissimilar material joining using high-strength DP 1180 steel and carbon fiber reinforced plastic (CFRP). Laser power, irradiation time, die geometry, and rivet geometry were considered as variables, and their effects were analyzed and compared. The results indicated that laser-assisted thermal treatment enabled the SPR process for high-strength steel. Increasing laser power and irradiation time expanded the heat-affected zone and reduced hardness to approximately 250 HV in the region where rivet flaring occurred, leading to martensitic transformation into ferrite and tempered martensite. Process variables significantly influenced SPR joint quality, including failure mode and fracture load. The lean die angle resulted in stable joint formation, while the steep die angle led to lower sheet detachment due to increased deformation demand. Longer rivets improved interlock formation and fracture load; however, the fracture mode shifted from rivet pull-out to CFRP failure. The results confirmed that laser-assisted thermal treatment enabled the SPR process for high-strength steel, and its effectiveness depended on die and rivet selection in ensuring robust SPR joints.