Research On Laser Welding Process And Joint Microstructure And Properties Of Automotive High-strength Steel

The third-generation advanced high-strength steel QP steel has excellent tensile strength and elongation and has excellent energy absorption performance during collision deformation.It is often used in key anti-collision reinforcement structures such as the A-pillar and B-pillar of the automobile body.The application prospects for lightweight car bodies are broad.Laser welding is widely used in automobile manufacturing due to its advantages of high flexibility,large penetration depth to penetration width ratio,and small deformation.Therefore,this paper carries out relevant research work on the mechanical properties and microstructure evolution of laser welded joints of the third-generation advanced high-strength steels QP980 and QP1180 with different strength levels.The main contents of this article are as follows:(1)In this paper,the macro morphology,microhardness,tensile properties,microstructure distribution,changes of weld center elements of QP steel welded joints under different heat input conditions were tested and characterized,and the laser welding process of QP980/QP1180 high-strength steel was studied.,To obtain a reasonable heat input process parameter window;(2)This article uses two methods to change the heat input,one is to control the laser power unchanged,change the welding speed to change the heat input,and the other is to control the welding speed unchanged,change the laser power to change the heat input,and study the effect of heat input on QP steel.The influence of laser-welded joints on the microstructure and performance and the comparison of the weight of the influence of laser power and welding speed on the microstructure and properties of welded joints under the same heat input conditions;(3)Analyze the crystal morphology of the welded joints of QP980/QP1180high-strength steel with the same quality and different strength under different laser heat input conditions and the changes of the elements in the fusion zone of the joint weld.Analyze the microstructure distribution of representative welded joint fusion zone and heat-affected zone;Combining the simulation of the temperature field and microstructure evolution of laser welding of QP steel,explore the evolution mechanism of the microstructure of the weld under the action of temperature thermal cycling and research the softening mechanism of the heat-affected zone of the welded joint.Analyze the reasons for the softening of the heat-affected zone under the action of thermal cycling.