One thin 5000 series aluminium alloy sheet and two thin 980 MPa grade cold rolled ultra-high strength steel sheets were joined by self-pierce riveting and mechanical clinching processes. The joinabilities for a combination of the aluminium and steel sheets in both processes were investigated for different die shapes in the experiment and finite element simulation. In self-pierce riveting, the three sheets were successfully joined for both combinations of the upper and lower aluminium alloy sheets by optimizing the shapes of a die and rivet. In mechanical clinching, the three sheets were successfully joined by an optimum die for the configuration of the upper aluminium alloy sheet. On the other hand, the three sheets for the configuration of the lower aluminium alloy sheet were not joined even by optimizing the die shape in the both finite element simulation and experiment, because the material flow of the steel sheets was insufficient to form the two interlocks. The tension-shear loads for the clinched and riveted sheets with the adhesive were almost the same, because the load for the adhesive was the highest. In the cross-tension test, however, the load by the adhesive was comparatively small.
Keywords: aluminium alloy sheet; joining; joint strength; mechanical clinching; plastic deformation; self-pierce riveting; three sheet; ultra-high strength steel sheets.