Welding Technology And Performance Optimization Of Aluminium Alloy Bumper

Aluminum alloy has excellent physical and chemical properties,mechanical properties and good processing properties.It is currently the second most popular material in the production and life of steel.It is widely used in automobile body-in-white and various automotive safety parts.Aluminum alloys,which are currently widely used in body construction,can reduce the weight of vehicles by 20-30%,which can reduce fuel consumption by about 10%.The connection between the various parts of the car is inseparable from welding,and the quality of the welding basically determines the overall rigidity of the car body.Therefore,how to further improve the welding quality of aluminum alloy to achieve high-efficiency and high-quality welding of aluminum alloy is a difficult and hot issue in current research.In this study,the aluminum alloy bumper was taken as the research object,and the welding experiments of 6063 and 6082 aluminum alloys with different CMT welding processes were carried out using a new CMT TPS 500i welding machine.The effects of different CMT welding processes on the microstructures and properties of 6063aluminium alloy welded joints were studied.The effects of external alternating magnetic field on the welded zone formation,microstructures,mechanical properties,pore distribution,growth and escape mechanism of 6063 aluminium alloy welded joints were studied.By studying the strength loss of the main welded joint?T-weld?in the bumper and simulating the bumper collision,the effect of the strength loss on the bumper collision results was studied and evaluated.The main research contents and results are as follows:Three different CMT welding processes?CMT,CMT MIX and CMT MIX+Synchropulse?were used to weld 6063 aluminum alloy sheets.The effects of different CMT welding processes on the structure and properties of welded joints were studied.The results show that full penetration weld without obvious spatter can be obtained under all three processes,and almost perfect fish scale weld can be obtained by CMT MIX+Synchropulse process.Under CMT MIX+Synchropulse process,the arc penetration and stirring effect are more obvious,and the cross section shape of welded zone is from"V"type to"X"type.By using the process characteristics of CMT MIX+Synchropulse,the problems of hot crack and low fluidity of molten pool caused by using Al-Mg welding wire were solved.The microstructure of 6063 aluminum alloy CMT MIX+Synchropulse welded joint with ER5183 welding wire is equiaxed grain+dendrite,and the eutectic structure of?-Al+Mg is mainly distributed at the grain boundary and between dendrites of?-Al.The welded zone center structure of the two welded joints is a large number of equiaxed crystals.The average grain size of welded zone of ER4047 welded joint is 78.5?m,which is smaller than the grain size of welded zone of ER5183 welded joint,which is 103.2?m,and the grain is remarkably refined.The equilibrium crystal phase?-Mg₂Si precipitated in the welded zone and the coarsening and overaging softening of the grains in the heat-affected zone resulted in significant softening of the welded zone and heat-affected zone.As the grain refinement of welded zone improves the strength of welded zone,the welded joint eventually breaks in the weaker heat-affected zone.The tensile strength of the two welded joints can reach 68.2%and 70.2%of the base metal,respectively.In order to effectively reduce the porosity of the welded zone,the alternating magnetic field was introduced to stir the molten pool.The shape and trajectory of arc are changed by adding magnetic field.With the increase of excitation current,droplets spiral irregularly around the center of welding wire,resulting in the shape of cross section of welded zone from"chuan"type to"X"type to"V"type.The dendrites formed in the solidification process of the molten pool break up under the action of magnetic field.The dendrites formed during the solidification process of the molten pool are broken under the action of the magnetic field.The broken dendrites are dispersed in the molten pool to become heterogeneous nucleation sites,and the nucleation rate is increased.The center of the welded zone is organized into a large number of fine equiaxed crystals.The grains are significantly refined.With the increase of excitation current,the porosity of welded zone first decreases and then increases,and the minimum porosity is only 0.32%.In T-type welding,the weld pool on the side of 6082 aluminum alloy with high Si content has a high cladding amount.With the increase of heat input,the T-type weld transition from crescent to bowl.Without considering the strength loss,the maximum stress?344.5MPa?occurs at the contact point between the bumper and the pendulum.Aluminum alloy bumper is not completely crushed at the end of the collision process,and the overall energy absorption and collision avoidance effect of the bumper is better.Unlike the strength test results of welded joints,the upper and middle parts of the anti-collision beam and the middle part of the energy absorbing box are eventually damaged after the collision,rather than the joint of the two.Considering the strength loss,the contact parts between the two ends of the anti-collision beam and the energy absorbing box will be broken first.