Effect of Weld Line Energy on Mechanical Properties and Formability of Cold Metal Transfer-Welded Dissimilar DP600-780 Thin Sheets

In this study, the effect of weld line energy (WLE) and root gap on the mechanical properties and formability of cold metal transfer-welded dissimilar dual-phase (DP) steel thin sheets was investigated. 1.2-mm sheets of DP600 and DP780 were joined with varying WLE 66.45 J/mm to 219.34 J/mm at zero and 0.2-mm root gap. The microstructural features and mechanical properties were analyzed through field emission scanning electron microscopy, Vickers microhardness analysis, uniaxial tensile test and Erichsen cupping tests. The results indicate that WLE and root gap significantly affect the bead shape, formability, tensile strength and microhardness. The joints with root gap exhibited superior mechanical properties and formability compared to zero-gap joints. The highest tensile strength (668.35 MPa) and hardness (367 HV_0.5) were achieved for joints with 0.2-mm gap at 66.45 J/mm. This joint also achieved the highest joint efficiency (102.59 %) and the least heat-affected zone (0.828 mm). The highest Erichsen index (6.82 mm) was achieved for 219.34 J/mm joint with 0.2-mm root gap. Fractography results confirmed ductile fracture.