Research Of Inverter Resistance Spot Welding Process Of High Strength Dual-phase Steel

The hot dip galvanized dual-phase steel has high strength and good corrosion resistance as well as good punching performance. It has become the main steel used in the automobiles of light quality and high safety in the future. At the same time, due to the surface zinc coating of the high strength galvanized steel, the traditional spot welding will cause serious spatter problem. The strength of the galvanized steel welding joints cannot meet actual production. The invent resistance spot welding technology could meet the new welding demands from the high strength galvanized steel, that is, stable welding current, fast dynamic response and high control precision. Therefore, it is of great practical significance for the investigation for the welding performance of the high strength galvanized steel.The recent development of the research on the spot welding of dual phase steel is introduced in this paper. Many groups of spot welding experiments of DP590GA dual-phase steel with different welding specification are carried out. Nugget diameters are measured under different combination of welding parameters, and mechanical properties of weld joint are measured by cross-tensile test and tensile-shear test. When the welding current increased from 7.3kA to 9.5kA, weld nugget sizes and strength of welded joints increased with the increase of welding current. But when the welding current increased to a certain extent (greater than 9.5kA), the heat input was so much that the liquid metal in the nugget which had been melted got splashed, as a result, the strength of spot welded joints got reduced. DP590GA nugget microstructures which were founded to be the columnar crystals, mainly contained a great deal of large lath martensite and a small amount of ferrite and pearlite.At the same time, the paper has researched quality analyzing system based on dynamic resistance for resistance spot welding, which can real time monitor spot welding current, welding resistance and electrode force. With relative analysis of the information of all parameters beside perfective and defective weld spots, we can judge the quality of weld spot by using what it outputs before.