The Effect Of Laser Welding On The Organization And Performance Of DP Steel

Entering the21st century, because of the concept of energy crisis and low-carbon energy-saving deeply rooted, the automotive industry is undergoing constant innovation and a wide range challenges. On one hand, energy conservation, on the other hand, improving the car crash safety performance. The use of high strength automotive steel and laser welding technology can realize the car light weighting and improve the safety performance of motor vehicles. Dual phase steel is currently being widely used as high-strength automotive steels. It has a low yield strength, high work hardening index, no yield extension and other features. In addition, laser welding has many advantages such as reducing the number of parts and molds, reducing the number of welding spot, optimizing material consumption, reducing part weight, reducing costs and improving machining accuracy. Dual phase steel has been used by many large car manufacturers and parts suppliers. Because the dual phase steel and its laser welding materials are applied more widely in the automotive, it is important to research the microstructure and properties of dual phase steel and its laser welding materials.Firstly, the paper studied the microstructure characteristics of dual phase steel and its deformation behavior at different strain rates. Secondly, the DP600steel was welded under different process parameters. The effect of various parameters on the welding quality are analyzed. And optimum welding process was obtained.The above results show:(1) DP600steel microstructure are ferrite and martensite; Hardness is200HV; with the increase of strain rate, yield strength, tensile strength and yield ratio of DP600steel are increases, while plasticity decreasing firstly then rising and finally decreasing; fracture type of DP600is toughness fracture.(2) The defocus distance, pulse width, welding speed, welding current, welding frequency and other welding parameters have the great impact on the welding process, welding joint geometry, and the surface morphology of welding sample. And the optimum process parameters for laser welding of dual phase steel were summed up by experiment. (3) The welded joint of DP600steel can be divided into three areas:â‘ fusion zone, Microstructure are a small amount of tempered martensite and martensite, hardness was significantly higher than the base metal, up to1.7times;â‘¡heat affected zone, microstructure is ferrite, martensite, tempered martensite and bainite, there are softening zone;â‘¢base metal, microstructure and hardness of this area are the same with DP600steel.(4) With strain rate increasing, yield strength, tensile strength and yield ratio of welded sample are increase; while plasticity decreasing firstly then rising and finally unchanging; fracture type of welded sample is toughness fracture.(5) After laser welding, the plasticity of the DP600welded sample was significantly higher than the base metal; the yield strength and yield ratio of welded sample were significantly higher than that of base metal in the low strain rate, and with strain rate increasing, the gap was gradually decreases finally identical; tensile strength of base metal was significantly higher than welded sample, and with strain rate increasing, the gap was gradually decreases finally identical.