Welding Thermal Cycle’s Effect And Mechanism On Aluminum Alloy Joint Properties

In order to reach the requirement of safety,comfort,lightweight and energy-savingof high-speed train,it’s main trend to use aluminum alloy materials as main bodystructure.5083and6N01aluminum alloy are two kinds of aluminum alloy commonlyused in the manufacture of high-speed trains,and both of them have good properties ofwelding and forming.Common international and domestic problems of high-speed trainsare reflected,which is that cracks is inevitable when the train body is under dynamicloads.In order to avoid the occurrence of major accidents, and ensure safety and stableoperation of high speed train,people have to repair serious defects like cracks timelyonce or even many times.However,aluminum alloy repair welding is a process ofwelded joint repeatedly heated.People need to do more investigation about the negativeeffect.In the research,I finished welding and one to three times repair welding processusing5083,6N01and ER5356welding wire.Through static tensile tests,obvious neckingphenomenon appeared in6N01aluminum alloy heat affected zone,but couldn’t befound in5083aluminmum alloy heat affected zone,indicating that6N01aluminumalloy heat affected zone had good plasticity.Through bending tests,5083had strongbending capacity,while6N01two and three times repair welding joints had weakbending capacity,which meant the times of repair welding had an effect on themechanical properties of welded joints.Through the structure analysis andmicrohardness tests,the times of repair welding led to material growth.5083aluminumalloy deformation strengthening effect was weakened,and there was overaging in6N01repair-welding joints.Fatigue tests were completed and the corresponding S-N curves wereobtained.Through S-N curve fitting calculation,I got fatigue limit and assessed thefatigue performance of welding joints.Though crack growth rate test,I obtained fracturemechanics parameters under different repair welding condition.Simulation and testswere done to master the residual welding stress distribution.I finished the analysis of theresidual life considering different work force,different initial crack length and differenttimes of repair welding. The conclusion is that,weld is the weak link of5083aluminumalloy,and HAZ is the weak link of6N01aluminum alloy.The fatigue properties ofaluminum alloy decreased when the times of repair welding increased.Compared to6N01,5083has better fatigue performance.