Effects of double pulse welding on microstructure, texture, and fatigue behavior of DP590 steel resistance spot weld

In the present study, dual-phase (DP590) steel sheets were joined using single-pulse and double-pulse resistance spot welding in lap joint configuration. Effects of the welding method on microstructure, texture, tensile shear properties (load carrying and energy absorption capacity), and fatigue strength of welded joints were investigated. Tensile shear test results showed that double-pulse weld exhibits an average of 15.6% and 83.1% higher peak load and failure energy, respectively than single-pulse weld. Fatigue test results showed that double-pulse welds withstand 10.8%, 22.7%, 1.8%, 158.7%, and 20.2% higher number of cycles than single-pulse welds at an applied load of 2.3, 2.76, 3.45, 4.6, and 8.1 kN, respectively. The better mechanical performance of the double pulse spot welds is attributed to the large nugget size resulting in higher bonding area, the tough microstructure of the nugget consisting of tempered martensite structure, acicular ferrite, and Widmanstätten ferrite, and the formation of randomly orientated grains with a high fraction of high angle boundaries in the fusion zone, which resulted in improved resistance to crack propagation during mechanical loading.