A systematic experiment was performed for four types of welding circuit with different circuit inductances and a common welding coil, where each circuit inductance is given by the sum of a different remaining inductance and a common effective inductance. It was demonstrated that increasing the circuit inductance causes adverse effects on the discharge current, resulting in a long first collision time and a low deformation velocity of the moving sheet. When the circuit inductance increases from 0.0587 μH to 0.2280 μH, the maximum current decreases from 223 kA to 132 kA at a discharge energy of 2.0 kJ. With the decrease in discharge current, the deformation velocity of the sheet decreases from 383 m∙s^-1 to 164 m∙s^-1. The higher the circuit inductance is, the lower the deformation velocity of the sheet is. With the lower velocity, the shearing load of the resulting welded sheet further decreases, ultimately leading to joining failure. However, in the circuit with a minimum inductance of 0.0587 μH, it is possible to weld an aluminum alloy sheet to a 1 GPa class high-strength steel sheet. It has been clarified that the decrease in circuit inductance improves the joining property of a welded sheet.

A T5-treated aluminium die casting and a high strength steel sheet component were joined by self-pierce riveting using a rivet having a single length. The problems of large thickness variation and low ductility of the aluminium castings in riveting were solved by optimising the shape and hardness of the rivet and die. The edge cracking of the aluminium casting was prevented by applying pressure to the edge via the holders. The aluminium casting having large thickness variation and low ductility was successfully joined with not only a 590 MPa but also a 980 MPa ultra-high strength steel sheet.