Joining TWIP to TWIP and TWIP to aluminium: A comparative study between joining processes, joint properties and mechanical performance

In the present study, Resistance Spot Welding (RSW), Self-Piercing Riveting (SPR), Kerb Konus Riveting (KKR) and EJOWELD techniques were investigated for joining of TWIP steel sheets with one another and with Al. This is the first time the KKR and EJOWELD methods were compared to conventional joining methods The main focus was on the mechanical properties of similar joints produced between Zn-coated Fe–12Mn–1.5Al–1Si–0.5C Twinning Induced Plasticity (TWIP) steel and dissimilar joints between Zn-coated TWIP and Al 5754 or Al 6111 aluminium alloy sheet. The nugget solidification after fusion welding was evaluated through characterization with SEM-EBSD. In the case of RSW produced joints it was found that the joints with smaller grain size and larger orientation diversity exhibited larger maximum load capability. Regarding the joints produced with the EJOWELD method, grain size did not vary much compared with the base metal. Mechanical properties and the fracture behaviour of these joints were identified through the application of the lap shear method and failure modes. In the case of TWIP/TWIP combination, the results demonstrated that RSW samples exhibited the highest maximum load and corresponding elongation, while in dissimilar joining, SPR exhibited the largest maximum load. The EJOWELD method for the dissimilar joints showed similar mechanical properties to the SPR, in terms of maximum load, while KKR poorer properties. By comparing the mechanical properties of all the joints, it can be concluded that the primary factor of joint strength in RSW were the joining parameters (preweld and number of weld currents, welding time), while in the case of the other techniques it was the sheet strength.