Effect Of Electrode Pitting On Nugget Formation In Resistance Spot Welding Of Galvanization High Strength Steel

Galvanized high strength steel is a kind of advanced high strength steel material with high strength,good corrosion resistance and good stamping performance,can meet the needs of light weight and safety,and largely applied in auto-body manufacturing.But compared with orinary low carbon steel,galvanized high strength steel had serious electrode wear and obvious pitting change in spot welding,which had great effect on nugget formation.Therefore,it is of great significance to study the effect of pitting corrosion on nugget formation.In order to solve the negative influence of pitting corrosionon nugget growth,the spot welding process of galvanized high strength steel and nugget growthhave been studied in this paper.First,the influence of pitting corrosion on the contact resistance and contact thermal resistance between the electrode plate and the electrode was analyzed.The effect of pitting on the distribution of contact stress was obtained by the numerical analysis of the structure model.Pitting corrosion not only increased the contact resistance between the workpiece,but also reduced the thermal conductivity and changed the distribution of the contact stress.Stress concentration occured at the edge of pitting obviously.Second,the relationship model of pitting corrosion on nugget formation were established.The influence of pitting corrosion on the contact area,current density distribution and temperature distribution between the electrode and the workpiece as well as between the workpiece and the workpiecewas analyzed.Theeffectof pittingon nugget formation was revealed in spot welding of high strength galvanized steel,which can provide theoretical basis for the optimization of welding parameters and process optimization.The pitting increased the actual contact area between the workpiece,reduced the current density and the nugget diameter.The distribution of the current density and temperature is changed by the generation of pitting area,the nugget formation is encumbered largely.With the increase of the pitting area,the probability of the formation of the ring is increased.Do spot welding experiments to galvanized high strength steel in the same condition ofsimulation,prepare low magnification metallographic photos of joint,and measure nuggetdiameter.Experimental results and simulations are in good agreement,which verify the effect of pitting corrosion on nugget formation.The welding parameters can be optimized by analyzing the influence of welding parameters on the weld nugget,which can provide theoretical basis for the optimization of welding parameters and process optimization.