Numerical Simulation Of Material Flow And Dynamic Recrystallization Of Friction Stir Welding Of TC4Titanium Alloy

Friction stir welding (FSW) as an advantageous, efficient, clean and energyconserving solid state joining method, has been widely used in the manufacturingfields of aerospace, ships, airplanes and vehicles. Hitherto, scholars all over theworld have already carried out a series of experimental research on it, but as acomplicated process combining frictional heating, metal flowing and microstructure transforming, FSW leaves a lot of physical mechanism to be studied andillustrated, which is difficult for experiments. However, numerical modeling methodnot only lowers the costs, but also provides dynamic observation on the wholewelding process, which is a guideline for practical production.In this paper, FSW heat source model is firstly established by numericalmodeling method applying finite element modeling (FEM) analysis softwareMSC.Marc and secondary development on it using FORTRAN language, fulfillingtemperature field modeling in different phases. The whole welding process isdivided into three phases, namely needle inserting, preheating and head marchingphases. The welding head rotates at a rate of800r/min, and marches at a speed of0.6m/s. When preheating time is15s, temperature around welding head basicallyreaches the requirement for welding. During the marching phase, temperature fieldkeeps basically stable. From computing results, the shape of temperature field isellipsoid and in the front area temperature gradient is larger. This mainly concernsthe heat conducting property of the material.Afterword, based on temperature field modeling, the metal flow field aroundthe welding head is simulated numerically using FEM analysis softwareDEFORM-3D. Parameters are set referring to temperature field modeling results.An analysis on the whole shows that the metal around the welding head flows into ahopper-like zone similar to the shape of welding head, and the flowing field isasymmetrical with the welding seam. By studying the metal flow in differenthorizontal cross sections, it is found that nod velocities increase linearly with thedistance from seam center, and material flowing ability weakens when the weldingseam is deepened. By changing the rotating rate and marching speed, heat input isaffected. In some range, heat input increases with the rotating rate, leading to a better flowing ability of metal and a better welding seam forming. This regularitygoes similar with the decrease of marching speed.Finally, the dynamic recrystallization process in the nucleating zone of thejoint is simulated numerically. The grains changing regularity in dynamicrecrystallization process in the nucleating zone is studied numerically withoutapplication of strain and strain rate. It shows that with the increase of strain, theaveraged dynamic recrystallization grain size becomes smaller, and fractions ofdynamic recrystallization increase. With the increase of strain rate, grain sizedecreases gradually.