Numerical Simulation Of Resistance Spot Welding Process Of DP590 Dual-Phase Steel And Experimental Analysis

The dual-phase steel is the ideal automotive steel for its combination of high strength and excellent formability. It has being the main steel used in the automobiles of light weighting and high safety in the future. Resistance spot welding is the main jointing technique in the automobile manufacturing. Compared with normal low-carbon steel, the dual-phase steel is added to more alloying elements such as Si and Mn, so it is possible for the welding joint zone to result in problems like segregation, quench hardening embrittlement and prone to welding defects. Therefore, to be able to widely use the steel, it is very important to confirm suitable welding parameters and establish optimum spot welding specification. Numerical simulation has been the main research method in resistance spot welding since the forming process of nugget is hard to observe.The recent development of the research on the spot welding of dual phase steel and the application of numerical simulation on spot welding are introduced in this paper. Furthermore, characteristic and theoretical background of finite element software SORPAS which is specially designed for resistance welding are also briefly introduced.Based on the environment of software SORPAS, an axial symmetric finite element model for the spot welding process of DP590 dual-phase steel is established. Thermophysical properties parameters of DP590 are tested for this simulation. By researching numerical simulation, the variation rules of temperature field, electrical field and contact resistance are discovered quantitatively, and nugget diameter, distribution of hardness, cooling rate and microstructure of weld joint zone are calculated.Many groups of spot welding experiments of DP590 dual-phase steel with different welding specification are carried out. Nugget diameters and hardness distribution are measured under different combination of welding parameters, and mechanical properties of weld joint are gained by cross-tensile test and tensile-shear test. The effect rule of welding time, welding current and electrode force to nugget diameter and mechanical properties are researched. The SH-CCT curve of DP590 dual-phase steel is determined by practical experiment. Finally, the simulative results with the experimental results are compared, and the computational nugget diameter, shape and penetration agree well with those from experiments, which show that the models and simulation results in this paper are reliable.Using the software SORPAS to simulate slow cooling and tempering process under different combination of welding parameters, then put the optimum combination of parameters into practical spot welding experiment. By means of tensile test, hardness test and fracture scanning analysis, the results show that the toughness of spot weld joint of DP590 can be obviously improved by attaching suitable slow cooling impulse or tempering impulse specification.