| Under the general trend of environmental protection,energy saving and safety in today’s world,lightweight has become an important development trend in the automotive industry.High-strength aluminum alloy has excellent comprehensive mechanical properties and moderate cost.Its superior energy absorption characteristics and good resistance to deformation are suitable for body structural parts and internal reinforcing plates,and have a broad prospect of use.Friction stir welding is widely used in the welding of light alloys such as aluminum and magnesium,and is gradually being applied in automobile manufacturing.In this paper,the 6061-T6/7075-T6 aluminum alloy with a thickness of 2mm is taken as the research object to study the microstructure and mechanical properties of friction stir welding joints under different welding process parameters and the parameters of welding process.The effects of dissimilar aluminum alloy friction stir welded blanks on the deformation and energy absorption performance of the front longitudinal beam of the car and the intrusion of the front wall are studied,which provides a theoretical basis for the use of 6061-T6/7075-T6 aluminum alloy on the car.First,a single variable method was used to conduct friction stir welding test.The welding speed,stirring head rotation speed and plate placement position were used as variables to prepare different performance aluminum alloy tailor-welded plates.When the7075-T6 aluminum alloy is placed on the forward side,the joints under various parameters have achieved a good connection.Optical microscopy and field emission scanning electron microscopy were used to analyze the microstructure evolution and grain structure evolution of the joint.Joints can be divided into weld nugget zone,heat engine affected zone,heat affected zone and base metal zone.Dynamic recrystallization of SZ occurs,the structure is fine equiaxed crystals,and the texture is weakened;TMAZ does not undergo complete dynamic recrystallization,its grains are stretched and bent,and the dislocations slide along the direction of deformation to produce a large number of small angles grain boundary,the brass texture is weakened.Changes in welding process parameters affect the average grain size of SZ,TMAZ,and SZ,which decreases with increasing welding speed and increases with increasing rotational speed.Secondly,temperature and torque measuring equipment is used to measure its process parameters.The peak temperature on the advancing side is lower than that on the retreating side.The peak temperature decreases with the increase of the welding speed and increases with the increase of the rotation speed;The welding speed increases and decreases with increasing speed.The mechanical properties of the joints were measured using a micro hardness tester and a universal tensile testing machine.The hardness of SZ and TMAZ was significantly lower than that of BM.With the increase of welding speed and speed,the maximum tensile strength and elongation of the joints increased first.Postdecrease trend.The optimal process parameters are welding speed 150mm/min,stirring head speed 1000r/min,7075-T6 placed on the forward side.According to fracture metallography and SEM image analysis,the fracture position of the joint is located in RSZ,mainly presenting ductile fracture mode.Finally,through the Hyperworks and LS-DYNA software,the vehicle model is subjected to a frontal collision simulation.During the frontal collision,the deformation of the front longitudinal beam of the car and the energy absorption performance have a greater impact on the safety of the occupant.The layout plan of the plate making has improved energy absorption characteristics and reduced deformation,and greatly reduced the amount of intrusion of the front wall.While ensuring the crashworthiness of the car,it has improved the lightweight level of the car. |
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