Macro And Meso Scale Simulation Of Vibration Reduction Of Welding Residual Stress For Aluminum Alloy

The welding residual stress is concentrated in the welded joint area,and the high internal stress that remains in the structure after cooling will be released with the service time,causing the structure to deform,leading to the decrease of strength,dimensional accuracy and service life.Compared with the traditional heat treatment method,vibration has the advantages of low energy cost,simple operation and short processing time,so it has been widely used in the post-welding treatment in recent years.However,the selection of vibration parameters of this technology often depends on a large number of test results,which increases the time cost while the stress reduction effect is uncertain.In the prediction of residual stress of vibration reduction by numerical simulation,due to the obvious orientation of grain growth in weld zone,the macroscopic isotropic model can not effectively reflect the micro-stress evolution in real crystals,and there is a large deviation between the simulation results and the test results.In this paper,the laser-welded 1060 Al alloy sheet was taken as the research object,and the bending vibration test method was used to study the influence of vibration on the stress reduction of the specimen with different heat input and different vibration amplitudes as the initial conditions.Bending vibration is to fix one end of the specimen and exert reciprocating displacement on the other end.In the process of reducing the residual stress,only the influence of plastic deformation on the residual stress is considered.At the same time,the finite element simulation software Abaqus is used to compare the stress changes caused by vibration at macro and meso scales more intuitively through the finite element method of crystal plasticity.At the macroscopic scale,the temperature field and macroscopic stress field of the specimen are calculated by thermoelastoplastic method.At the meso-scale,a three-dimensional polycrystalline model was established in the weld center according to the structure and orientation of the aluminum alloy cell,and the distribution of meso-stress under different heat input was analyzed.In the process of finite element simulation,the difference between the reduction of meso-stress and macro-stress caused by vibration is emphatically studied and compared with the experimental results.The results show that the residual stress after welding increases with the increase of heat input.After bending vibration,the higher the initial stress vibration,the more obvious the stress reduction is.With the increase of vibration amplitude,the effect of stress removal is improved,and the amplitude of increase decreases with the increase of vibration amplitude,and the longitudinal residual stress cannot be completely eliminated.The EBSD image of the weld center shows that with the decrease of the heat input,the growth trend of the columnar crystal gradually changes from a curve to a straight line,and the length-width ratio of the columnar crystal tends to be slender.The results of meso-stress field simulation show that the residual stress distribution is correlated with the crystal orientation.The interface of grains with large orientations difference will produce a higher stress concentration phenomenon,while the columnar intergranular stress with similar orientations is smaller.The polycrystalline model with large crystal orientation difference has the highest effect stress reduction degree.The comparison between the macro and micro simulation results and the test results shows that the stress reduction degree of the micro simulation results is higher than that of the macro simulation results,which is more consistent with the test results.Therefore,the study of crystal micromechanics at the micro scale should be of great value for promoting vibration elimination of residual stress in industrial production.