Microstructure and mechanical properties of DP590 galvanized dual-phase steel CMT welded joint

In view of welding quality problem of thin plate in automobile manufacturing and large demand of galvanized dual-phase steel in automobile industry, CMT lap welding experiment of DP590 galvanized dual phase steel with 1.0 mm thickness was carried out under welding parameters of arc length correction coefficient 0, wire feeding speed 3.0 m/min and welding speed 400 mm/min. Microstructure and mechanical properties of welded joint were studied by X-ray diffractometer, scanning electron microscope and Vickers hardness tester. The experimental results showed that welded joints with good formation were obtained by CMT welding of DP590 galvanized steel. Microstructure of weld was mainly lath martensite. Coarse grain zone was composed of lath martensite and a small amount of ferrite. There were more martensite and a small amount of bainite in fine grain zone. In the incomplete phase transformation zone, ferrite content increased, while martensite content decreased. Tensile test of welded joints showed that fracture locations were in incomplete phase transformation zone, which belonged to plastic fracture. And the maximum load was 10.48 kN, which was close to that of base metal. The average microhardness of weld was the highest, about 260 HV. The lowest microhardness appeared in incomplete phase transformation zone, about 170 HV. The study provided technical reference for CMT welding of DP590 galvanized dual-phase steel sheet, and had important engineering significance for automobile lightweight production and manufacturing.Highlights: (1) Aiming at difficulty in welding of automobile steel sheet, CMT process with characteristics of low heat input welding was proposed.(2) Microstructure and mechanical properties of CMT welded joints of DP590 galvanized dual-phase steel were studied. The results could provide theoretical basis and data support for actual production of factories.