Study On Microstructure And Properties Of Laser Welding Joint Of Automotive Ultra-high Strength Hot-forming Boronsteal

Laser welding is an advanced connection technology, and widely used in automotive manufacturing industry. With characteristics of high efficiency, good quality welding line, small deformation of parts, it can effectively reduce body weight, improve stiffness of body structure. Hot-forming boron steel is the third generation of advanced automotive steel whose use proportion is increasing year by year, and is an effective solution to the contradiction between strength and formability of ultra-high strength automotive steel, and is mainly used in automotive safety components. Research found the study on hot-forming boron steel welding is still not enough at home and abroad, it is necessary to get more into the properties and microstructure of laser welding joint. Based on the support of the national science and technology major project, the study conducted CO2 laser butt welding experiment on quenched 22 Mn B5 boron steel plates. Then the paper observed weld profile, tested the mechanical properties of joint and analyzed the effects of process parameters, and finally using an optical microscope, scanning electron microscopy and electron back scatter diffraction(EBSD) technique to analyze the microstructure of joints and explore the mechanism. The results showed that: full penetration once forms, the degree of penetration and its cause of the heat source distribution changes become the main influence of profile. The heat-affected zone appears softening, and leads to the reduction of joint strength. The relationship of the weld profile shape, softening degree of heat-affected zone and tensile strength of joints with P/ν are all not a simple function relationship, because of the significant non-linear change in laser energy utilization under different laser power and different speed. The width of softened zone caused by tempering is much larger than that caused by incomplete quenching, then tempered zone weakens the effect of "bound to strengthen ", and is the main reason for decline of the joint strength.