Welding Process Stability And Defects Control Of Gmaw Welding On Zinc Coated DP590 With Lap Fillet Joint Used In Automobile

The zinc coating is the main factor affecting welding stability and defects of welding galvanized DP590, GMAW is used everywhere, this study was focused on making a stable welding and getting a low defect weld bead of gas arc metal welding of galvanized DP590 in a lap joint.In this study, the influences of welding stability consisting of lap joint, zinc, shielding gas were analyze, and an experimental scheme, in which welding parameters of welding mode, heat input and welding speed were contained, was designed to study the influences on welding stability. The experimental results demonstrated that the welding stability is similar in both short circuit mode and single pulse mode, but lower in double pulse mode. As heat input gets higher, the welding stability gets higher in both short circuit mode and single pulse mode, but the variation of welding stability is not obvious in double pulse mode. And when welding speed increases, welding stability decreases in short circuit mode, but shows an confusing variation in double pulse mode.The mechanism of porosity formation in welding galvanized DP590 was analyzed and the influences of welding process parameters consisting of welding mode, heat input, welding speed, modulated pulse frequency and wire feed speed deviation on the porosity were studied through an experimental scheme. The experimental results demonstrated that porosity decreases as heat input increases and porosity increases as welding speed increases in short circuit mode, porosity increases as heat input increases in single pulse mode, and when parameters are suitable, porosity is very low because of stir caused by the low frequency modulated pulse in double pulse mode.Talking into account both welding stability and porosity, lap joint of galvanized DP590 was welded in two optimal process parameters, X-ray was adopted to nondestructively test the welding seams and very little porosity was inspected; the microstructure of welding joint were analyzed and found not much soften tissue; the Vickers hardness test demonstrated that the base metal near the heat affected zone is the softest tissue; tensile-shear tests demonstrated that the strength of welding joint is enough as all the fracture are in the base metal.