Resistance Spot Welding Technology Of DP590GA Hot Dip Galvanized Dual-phase Steel And Numerical Simulation

The hot dip galvanized dual-phase steel has high strength and good corrosion resistance as well as good punching performance. It has become the main steel used in the automobiles of light quality and high safety in the future. Resistance spot welding is the main jointing technique in the automobile manufacturing. Compared with ordinary cold-rolled steel, the appropriate welding parameters range, which includes welding current, welding time and electrode force, will change greatly because of the base metal and surface zinc coating of the high strength galvanized steel. When welding, it may cause incomplete penetration or splashing which always leads to welding defects. Therefore, the study on the weldability and welding technology of high strength galvanized steel, will have an important impact on its wide use. Numerical simulation has been a 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 is introduced in this paper. Many groups of spot welding experiments of DP590GA 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 measured by cross-tensile test and tensile-shear test. The effect rule of welding current, welding time and electrode force to nugget diameter and mechanical properties are researched. And the macro and micro metallographic structure of nugget region are analyzed. Finally, some dynamic distribution curves of welding parameters are measured during the resistance spot welding process of DP590GA. Aiming at the zinc residue in the weld joint nugget of DP590GA, a double-impulse welding parameter with preheating impulse is designed to further improve its mechanical properties of the weld joint.And the recent development of the application of numerical simulation on spot welding is introduced in this paper. 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 symmetricfinite element model for the spot welding process of DP590GA dual-phase steel is established. Thermophysical properties parameters of DP590GA are tested for this simulation. By researching numerical simulation, the variation rules of temperature field and contact resistance are discovered quantitatively, and nugget diameter, distribution of hardness, cooling rate and microstructure of weld joint zone are calculated. Finally, the simulative results are compared with the experimental results, 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 feasible and accurate.The software SORPAS is also used to simulate the spot-welding process with preheating impulse. Compare the calculative result with that of the single-impulse spot welding of DP590GA, and further analyze the effect of coating on the contact resistance of the welding process. By means of tensile test and EDS analysis, the results show that the double-impulse welding parameter with preheating impulse of DP590GA can improve the mechanical properties of the weld joint, increase the nugget size, and reduce zinc residue in the nugget effectively.