Study On CMT Welding Process And Microstructure And Properties Of DP590 Galvanized Dual-phase Steel Joints

With the wider use of galvanized steel in car body manufacturing,more and more attention has been paid to the weldability of galvanized steel.Galvanized steel not only has all the good properties of dual-phase strength steel,but also has excellent corrosion resistance.The existence of galvanized layer on the surface of steel plate increases the difficulty of welding.How to improve the quality of lap joint of DP590 galvanized dual-phase steel is the focus of this paper.This paper takes DP590 galvanized steel as the research object,and the experiment adopts cold metal transition welding method,chooses 1.0 mm BHG-2M welding wire to overlap welding DP590 galvanized steel.The paper studies the microstructure,mechanical properties and weld porosity of overlap welding joint.The experimental results show that CMT lap welding of DP590 galvanized steel can obtain welded joints with good macro-forming,continuous weld seam and no welding defects.The weld zone is mainly composed of lath martensite,and the coarse grain zone is composed of lath martensite and a small amount of ferrite.The ferrite content in the incomplete phase transformation zone increases.Under the test conditions in this paper,the faster the welding speed,the narrower the heat-affected zone of the weld,the smaller the thermal deformation,the smaller the penetration width and depth-width ratio,and the smaller the grain size of the coarse-grained zone of the joint.And the faster wire feeding speed,the wider the heat affected area in the weld,the larger the thermal deformation,the wider the penetration width and the ratio of depth to width,and the larger the grain size in the coarse grain zone of lap joint.Tensile tests show that the fracture locations are in the incomplete phase change zone,and the maximum load is about 10 kN.The fracture of DP590 galvanized steel base material and welded joint specimens with various parameters has obvious dimples,which belongs to plastic fracture.The average hardness of weld zone is the highest and the highest average hardness value is about 280 HV,the average hardness of heat affected zone is slightly smaller than that of weld zone,and the average hardness of base metal is the lowest.The minimum hardness value appears at the junction of heat affected zone and base metal zone,and is basically consistent with the fracture location of tensile test,in the incomplete phase transformation zone.During welding,the larger the line energy and the smaller the welding speed,the lower the porosity in the weld.Zinc on the surface of the weld evaporates completely,and the damage of zinc layer on both sides of the weld gradually decreases with the weld as the center,and the zinc content increases with the weld as the center to both sides.In conclusion,CMT welding experiment of 1.0mm DP590 galvanized dual-phase steel can get good appearance and mechanical properties of welded joints.Finally,the optimum welding parameters suitable for the process of this paper are confirmed,the arc length correction factor is 0,the wire feeding speed is 3.5m/min and the welding speed is 400mm/min.