Multiphysics Field Coupled Model On Electronic Current Aided Friction Stir Welding Process

This thesis is supported by the National Natural Science Foundation EmphasesItem of China(51075413/E050803). Conventional friction stir welding(FSW) has beenwidely used in the welding of light metal alloys, but it till has many disadvantages inhigh melting point metal. In addition, welding defects of conventional friction stirwelding process mainly come from insufficient heat input. Electronic current aidedfriction stir welding(EFSW) process is proposed to overcome the shortcomings ofconventional friction stir welding. In this article, the whole process of electronic currentaided friction stir welding process is studied, and a three-dimensional finite elementmodel is established through multi-physics modeling technology using ComsolMultiphysics software.Firstly, a multiple physics fields numerical model of EFSW is proposed. Theestablished numerical model will be solved using multi-physics finite elementtechniques by strong fully coupling. Two non-linear solvers are employed to solve thisfinite element model. These two slovers are quasi-steady state solver and parametrictransient solver, respectively. The established model will solve the temperature field, thecurrent field and velocity field of EFSW and FSW process. And the results will be usedto study the difference between FSW and EFSW and characters of various kinds ofEFSW. The numerical results show that the resistance heat mainly generated on thecontact surface between the friction tool and the workpiece during the EFSW process.Preheating EFSW generates more heat in the region that has not been welded on theworkpiece and heat treatment EFSW results in more heat in the welded area. Theintroduction of current can effectively eliminates the asymmetry of temperature field inFSW. The electric field distribution can affect the distribution of temperature field.During EFSW process, materials of the workpiece have better fluidity, and becomeeasier to form the seam. As the current value ranging from50A to300A, the value ofmaximum speed also increases. As the current increasing, the asymmetry of the velocityfield becomes increasingly evident. The friction tool can reach the maximum value ofstress950MPa, and at the bottom face of the tool pin, the distribution of low stress areaexhibits a shape of a rectangle. Von Mises stress distribution in the lower surface of theshoulder is almost symmetrical distribution, but the distribution of volumetric strain isasymmetry. As the current value increase from50A to300A, the peak stress decrease, reducing from516MPa to415MPa.Finally, in order to verify the model in this article. In this paper, the temperature ofthe workpiece for both EFSW and FSW is measure by experiments. The results showedthat the experimental data are in good agreement with the simulated data, and therelative error is only2.1%. Experimental temperature data indicate that the temperatureof EFSW is always higher than the traditional FSW.