Comparing the weldability of AA6013-T4 aluminium alloy on DP600 dual-phase steel with laser welding and resistance spot welding

The welding of high-strength aluminium alloys on AHSS with laser beam welding (LBW) and resistance spot welding (ERW) is challenging due to the formation of brittle intermetallic phases. The weldability of a lap dissimilar joint between an AA6013-T4 aluminium alloy and a DP600 dual-phase steel with respect to microstructure and mechanical behaviour was investigated in this study. Microstructural analysis with optical microscopy shows that the ERW process did not show any significant dilution among the base materials. However, dilution and crack formation occurred in the fusion zone (FZ) during LBW. Martensite formed in the DP 600 dual-phase steel and liquation formed in the AA6013-T4 aluminium alloy within the heat-affected zone (HAZ) with both processes. X-ray diffraction and energy-dispersive X-ray spectroscopy analyses showed the formation of Fe₃Al intermetallic phases at the interface between the FZ and HAZ with both welding processes. Tensile test results showed no differences between the strength limits for both processes with an average value of 68 MPa. However, the shear deformation was 62% higher in samples welded using ERW. This study shows that dissimilar joint welding of AA6013-T4 aluminium alloy to DP600 dual-phase steel is possible, despite the formation of the Fe₃Al intermetallic phase, and that the ERW process is the most appropriate. (author)