Az31 Magnesium Alloy The Inverter Nugget Formation Process Of Numerical Simulation

Along with the rapid development of automobile industry, magnesium alloy has a vast potential for application, because energy saving and emission reduction has become an important subject. Because of resistance spot welding is one of the most commonly used welding methods in the process of automobile manufacturing, the numerical simulation in the formation of molten core of resistance spot welding will be beneficial to decide the proper technological parameters, improve quality of spot welding, and to promote the wider use of magnesium alloy in automobile industry.According to the elasto-plastic theory and the contact theory, considering the geometrical characteristics and heating characteristic in welding process, axisymmetric finite element model of stress field in preloading contact stage about magnesium alloys spot welding inverter is established. It simulated the contact behavior, got the initial conductive area and the pressure distribution state on the contact surfaces, and also analyzed the influence on the contact pressure by various kinds of factors. The contact resistance of inverter spot-welding process of magnesium was tested, and the influence of the condition of workpiece surface and contact pressure was analyzed. Based on the analysis of preloading contact, an axis symmetric finite element electro-thermo-mechanical model in the formation of molten core of resistance spot welding of magnesium is established. In consideration of the material performance model with temperature changes and the contact resistance, latent heat of phase change, and heat dissipation by cooling water and air, we analyze the changes of contact area and the distribution of contact pressure, current density and temperature on contact surface. Based on the result above, we made a further analysis on the changes of nuclear dimensions. A test for inverter spot welding of AZ31 magnesium alloy was done under the condition which is same with numerical simulation. Measured the offset of nugget and compared with the numerical simulation results. The result showed that the radius of contact surface between electrode and workpiece are equal to electrode's and the one between workpiece is close to 6.0 mm; contact resistance is decreasing with pressure increases; The contact pressure, temperature and current density are dynamic change, the spot which has a larger contact pressure also has greater temperature and current density, and the peaks of contact pressure is the location where the nugget first forms; the welding temperature field is expanding under direct current; the broadening of nugget along radial direction is faster, and the radial dimension has closed to the actual size when the nugget first forms; the offset of nugget in the experiment is same with the numerical simulation result when welding current is greater than 19KA.