Analysis of orthogonal test of properties of dual-phase DP600 steel resistance spot welded joint

The spot welding parameters for cold-rolled dual-phase DP600 steel in industrial trial production were optimized by orthogonal experimental design method with the tensile/shear loads of spot welded joints as the evaluation index. The welding window and optimal welding parameters were achieved by range analysis and variance analysis. The microstructure and tensile/shear loads of the spot welded joints under optimized welding parameters were investigated. The results showed that the welding current was between 9 000 A and 12 000 A,and the welding time was between 200 ms and 500 ms in the welding window.The welding current had most remarkable influence on the joint strength. With the increase of welding current,the tensile/shear loads increased. The maximum load 14 kN and the maximum absorbing energy 45.26 kJ were obtained with 12 000 A welding current,200 ms welding time and 2 500 N electrode pressure. And the microstructure of the resultant welded nugget mainly consisted of lath martensite.