Research on Resistance Spot Welding Process of SAPH440 Pickled Plate

The research object was SAPH440 pickling plate,the thickness was 2.0 mm.Comprehensively evaluated the mechanical properties of the joint by testing the shear and cross tensile properties,Axio Obersver A1 m optical microscope was used for microstructure and nugget diameter examination,and create spot welding process window.The result showed that,the pickling plate spot welding process window was 8.5 kA to 12 kA with a width of 3.5 kA,the nugget diameter and mechanical properties were positively correlated with welding current,when expulsion appeared,the nugget diameter and mechanical properties of the joint decreased slightly.The microstructure of nugget zone and HAZ were both martensite.Due to the influence of welding heat cycle,the structure morphology of the nugget zone was coarse and columnar,and the structure of HAZ was fine and needle-like.