| Magnesium alloys, which are machinable and recyclable, have the charactersof low density, high strength, high stiffness, good damping and good thermalconductivity. They have important applications in areas such as aerospace,transportation and electronics industry. The spot welding capability of Magnesiumalloys is not so good because of the good electric conductivity, the good thermalconductivity and oxides of Magnesium alloys with high melting temperature.Therefore, it is helpful to establish a reasonable specification of Magnesium alloyspot welding, to reduce the spatter and other defects, by simulating the process ofspot welding of Magnesium alloys.In this paper, The spot welding process of AZ31Magnesium alloy withthickness of1.2mm has been simulated, the heat and electronic coupled analysismodel has been create by finite element software Ansys. The influence of changingthe main parameters to Magnesium alloy spot welding temperature field has beenanalyzed, which has been proved by experiments. The shunt phenomenon in themulti-spots welding of Magnesium alloy has been simulated. The influence analysisof distance of spots in the multi-spots welding of Magnesium to the current ofshunting and the size of the melt-nucleus lays the foundation to optimize theparameters of Magnesium alloy spot welding and to establish the reasonable spotsdistance.The contact resistance of spot welding of Magnesium alloy has been measuredand calculated by voltammetry firstly. Then the temperature distribution in theheating time of spot welding of Magnesium alloy has been simulated and analyzed.In the beginning of the heating time, the temperature of the fitting surface of theworkpieces raised firstly and it melted at about0.12s to form a nugget. The nuggetincreased as the time increasing, and it formed a symmetrical oval-shaped nuggetfinally.The influence rules of changing the there main parameters to Magnesium alloyspot welding temperature field has been analyzed by using the same simulationmethod. The analysis result indicate: with the increasing of welding current, nuggetdiameter and penetration rates increase; The impact on nugget size of circular timeis similar to welding current but weaker; With the electrode pressure increasing, nugget diameter Change little, while penetration rate decrease significantly.The temperature field of multi-spots welding of Magnesium alloy has beensimulated by using two-dimensional model. The situation of shunting current hasbeen analyzed as the spot distance changing. The analysis result indicate: with thespots distance increased, the shunting current of Magnesium alloy spot weldingreduced, the impact to the nugget size decreased. The spots distance of Magnesiumalloy couldn’t be less than13mm, otherwise it should have a heat compensationbased on the actual situation.The experiments of Magnesium alloy spot welding was done in the samecondition with the simulations. Low Magnification metallographic photos of thejoints was prepared, nugget diameter and penetration rate was measured.Experimental result and simulations are in good agreement, which verify thesimulation method is reasonable and the simulation results are accurate.The shunting tendency of low carbon steel has been simulated andexperimented by using the same method. The result indicate that the influence ofthe shunting current in low carbon steel multi-spots welding is weaker than inMagnesium alloy multi-spots welding. The least spots distance of low carbon steelmulti-spots welding in the thickness of1.2mm is10mm. |
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