The Quasi-steady-state Heat-flow Coupled Numerical Model Of Friction Stir Welding

The FSW stable welding stage as the main stage of weld, the weldmenttemperature field and material flow field can be approximated that it reaches a stablestate. Therefore, it can effectively explore the weld forming by analyzing thetemperature distribution and material flow behavior of the weldment.During the friction stir welding process, the relative sliding occurs between thematerial and the tool resulted in the lower flow rate of the materials than the rotatingspeed of the tool. However, many simulation analyses, which based on fluid mechnics,can not effectively reflect the real flow behavior of the metal because of there is novalid wall conditions to describe the relative sliding. Therefore, a viscous slidingmathematical model and a coupled flow-thermal mathematical model were establishedbased on the relative sliding phenomenon and the interactions between thermal effectsand material flow respectively, and the numerical model would be built by usingCOMSOL Multiphysics finite element analysis software and verify the reliability of themodel in this paper. The weldment temperature distribution and material flow behaviorof6061-T6aluminum alloy during the quasi-steady-state welding processing would beacquired by using this numerical model, and they would be used to verify the reliabilityof the model, especially the reliability of the viscous sliding model. Finally, the effect ofthe sliping length on the material flow was discussed in this paper.The simulation results show that the temperature field which achieved from themodel measured the temperature which achieved from the experimental, the peaktemperature is781K, it is below the melting point of the material and the material doesnot melt. The weldment temperature distribution is oval which centering on the tool andradiates outward, the high temperature region in front of the tool is smaller than the rear,but the temperature gradient is bigger and the highest temperature region in the innerinside of the shoulder. Furthermore, the impact of the shoulder on the temperature issignificantly greater than the pin, which results in the decrease of the temperature withthe increasing distance from the shoulder, and this characterized in the cross section ofthe weld is particularly evident: the temperature distribution showed bowl which issimilar with the macroscopic of the weld line, the bowl on the narrow width and compete on low temperature, but it showed a asymmetry that the temperature of theadvancing side is higher than the retreating side.For material flow field, the flowing velocity under viscous sliding wall conditionis slightly than the sliding wall condition and the viscosity is slightly higher, but thevelocity and viscosity are similarity in the cross section and longitudinal section, thepeak velocity of the flowing material occurred in about90%of the shoulder radius andlower than the rotating speed of the tool, it shows that there is a relative slip between thematerial and the tool. The velocity and the radius of the flow area decrease with theincreasing of the sliding length and the viscosity increases. The flow regularity underviscous sliding wall condition is similar to the sliding wall condition, the material flowonly within the scope of the shoulder, some of which flow around the rotating tool, partof them accumulation in the retreating side and the rest deportees in the rear of the tool.Furthermore, the radius of the flow area and the fluidity decrease with the increasing ofthe sliding length.