The Effect of Current Mode on the Crack and Failure in the Resistance Spot Welding of the Advanced High-Strength DP590 Steel 05-14-01-0002

The causes of failure due to cracking in the resistance spot welding of the advanced high-strength steels dual-phase 590 (DP590) were investigated using scanning electron microscopy (SEM), optical microscopy, and the tensile-shear test. The results showed that by increasing the current amount, the formation of the melting zone occurred in the heat-affected zone (HAZ), leading to the cracking in this area, reducing the tensile strength and decreasing the mechanical properties; the initiation and growth of cracking and failure in this region also happened. In the HAZ, by increasing the current amount with the softening phenomenon, the recrystallized coarse grains also occurred, eventually resulting in the loss of mechanical properties. The results of the tensile-shear test also indicated that by increasing the current up to 12 kA, the strength was raised, but the ductility was reduced. At a higher current, the decrease in mechanical properties, strength, and ductility was noticeable. The optimum current amount and pressure were 10 kA and 4.2 kN, respectively; in this case, the maximum force was 22,000 N, and the maximum displacement was 10 mm.