| Friction Stir Welding which is an advanced Connection technology wasdeveloped by British Welding Institute (TWI) in1991for the aluminum alloy.Compared with traditional welding methods, it has characteristic of high-quality, highefficiency, low consumption, small deformation, no pollution, low cost.and so on.As a new solid joint technique, there is also a great deal of problems for frictionstir welding,such as the flow of material, temperature field and residual stress, need tobe studied widely. Most scholars at home and abroad researched thermal process andthe residual stress of the FSW by means of experiment and numerical simulation.Butonly a little research was about aluminum alloy sheets buckling deformation. So it isnecessary to integrate the numerical simulation and experiment to analysis theresidual stress and buckling deformation in the aluminum sheet FSW joints. Thenanalyze the feasibility ofthe prediction model.This paper investigates the residual stresses for friction stir welded3mmLY12alloy sheets in different parameters by using the blind-hole technique. To release theinfluence on the measuring accuracy of high welding residual stress when the holedrilling method is used, finite element modle of three dimensions was created tosimulate the test of the strain release coefficients. The strain release coefficientsA andB was corrected based on the energy parameter S which was obtained by the FEManalysis results. The results showed that longitudinal residual stresses areasymmetrically distributed at different sides of the weld center and it is high at theadvancing side and relatively low at the retreating side; like the longitudinal residualstresses, the transverse residual stresses are not at zero but about12.7%of base metal.The residual stresses will become larger at fist and have some decrease then with therotation rate and become more and more larger with the pressed-in and welding speed.On the other hand, a three-dimensional finite element model was established andthe temperature distribution in the FSW process was analyzed.Through imposing theboundary conditions in the temperature model，the heat source model of FSW wasdefined and the thermal cycle curve of the whole welding process was obtained.Theresults showed that the maximum temperature values were all in their high plastictemperature range.At last,the heat load obtained in the temperature distribution wasapplied to thecomponent model through indirect thermal coupled method.Theresistantstress and the thermal elastic-plastic buckling deformation of welded sheets were obtained. At the same time, the effects of welding speed, rotating speed and thereduced altitude on temperature and residual stress distributions were investigated.Theresults correlate well with corresponding experiments.The results of calculatingresistant stress showed that the longitudinal resistant stress of LY12joints were nearlyequal to the material yield strength. The difference between calculating andexperiment was large.But after calculating by inherent strain method and indirect heatcoupled methods which were based on the resistant stress, the result trend was assame as the experiment. At the same time, the relative deformation is anatomized welland errors were alllimited below20％.The results of buckling deformation showedthat there was high resistant stress in the aluminum sheets after FSW: which wasobviously higher than the experimental results.The numerical analysis results ofresistant stress and the experimental results showed the similar stress distributingtrend.This proved that it was feasible to prediet the resistant stress in FSW aluminumsheets through indirect heat coupled model and the inherent strain method is moretimesaver than the coupled thermal-mechanical method. |
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