Journal of Welding Science

In this study, 1 mm thick austenitic stainless steel 316L sheets were used for experimental testing. The experimental welding process was carried out using a Nd:YAG pulsed laser welding machine, and the welding simulation was performed using the SYSWELD software with a three-dimensional model for thermodynamic and mechanical analysis. The simulation results showed over 90% correlation with the experimental results. Analysis of experimental and numerical data revealed that at a constant voltage of 440 volts, decreasing the welding speed from 2 to 0.5 mm/s increased the overlap rate of pulses from 67% to 93% and the maximum average power density (EPPD) from 5963 to 21831 W/mm². Additionally, increasing the voltage from 440 to 480 volts at a constant speed of 1 mm/s raised the heat input from 114 to 138 J/mm and the weld depth from 0.56 to 0.66 mm. Due to the high cooling rate, the grain size of the weld metal became finer than the base metal (63% reduction in grain size). Two phases, austenite and ferrite, were observed in the weld metal, and the solidification mode was predicted to be FA.With an increase in welding speed from 0.5 mm/s to 2 mm/s at a constant voltage of 440 volts, the maximum tensile residual stress increased from 96 to 260 MPa due to reduced pulse overlap (from 93% to 67%), uneven heat distribution in the part, and the generation of thermal stresses. Furthermore, increasing the welding voltage from 440 to 480 volts at a constant speed of 1 mm/s caused the maximum tensile residual stress to rise from 124 to 152 MPa. The maximum hardness of the weld metal increased from 180 to 215 Vickers as the welding speed rose due to the prevention of carbon diffusion and an increased growth rate. However, with an increase in welding voltage and heat input (from 57 to 69 J/mm), the hardness decreased from 225 to 215 Vickers due to a reduction in thermal gradients and grain growth.

This study investigated the influence of resistance spot welding current intensity on the formation of liquid metal embrittlement (LME) cracks in galvanized advanced QP1180 steel. Galvanized steel sheets with a thickness of 1 mm were welded at currents of 6.5, 7, 7.5, and 8 kA. The results revealed that increasing the current significantly enlarged the weld nugget size, molten volume, electrode indentation, and the likelihood of LME crack formation. Microstructural analysis, elemental distribution, and crack characterization were conducted using optical and electron microscopy. The findings indicated that the weld zone microstructure primarily consisted of martensite, while the non-uniform distribution of zinc along grain boundaries facilitated the initiation and propagation of LME cracks. Cracks were predominantly observed at the periphery of the weld pool indentation and in the electrode-sheet contact area. This study demonstrates that controlling welding current intensity is a key factor in mitigating LME and improving the mechanical properties of joints in galvanized QP1180 steel. Optimizing welding parameters, particularly limiting current intensity, can prevent molten metal-induced cracking and enhance the durability and safety of automotive structures. Hardness profiling revealed peak hardness in the weld zone, followed by a gradual decrease toward the heat-affected zone (HAZ).

In this research, the influence of various forge pressure values and also the chemical composition of different carbon steels on rotary friction welding of SS 304 to carbon steels has been investigated. The steel rods of AISI 1015, 1030, and 1045 have been RFWed to SS 304 using 20, 40, and 80 bar forge pressure. Results indicated the 40 bar forge pressure as the optimum value, and by applying pressures below this number, the material flow in the weld interface would be tackled, resulting in improper mechanical values. By exceeding the optimum forge pressure, most of the viscoplastic material inside the weld interface would be rejected from that area in the form of flash, causing the weld to be done at a relatively low temperature. Microstructural investigation has been done by optical and scanning electron microscopes. Results showed that the weld zone is extremely fine due to DRX, and in the interface, a pro-eutectoid ferrite layer is formed, which has an increasing width when the heat input increases. Tensile test results showed that the optimum weld specimen is the RFW of AISI 1030 to SS 304 using 40 bar forge pressure, 40 bar friction pressure, 5s friction time, and 1500 RPM rotational speed. This specimen has shown 116 % joint efficiency and 715 MPa ultimate tensile strength.