Numerical modeling of friction stir welding of dissimilar metals using functionally graded material concept and its experimental verification.

摘要

To gain a better understanding of the Friction Stir Welding (FSW) of the dissimilar metals, Finite Element Modeling (FEM) of FSW process was advanced by the novel application of the Functionally Graded Material (FGM) concept to the welding zone. Modeling and numerical simulations were conducted by the Lagrangian FEM formulation and a time-varying FGM was implemented to simulate the change in material composition during the welding process. To verify the proposed models and concepts, experimental investigations of FSW were performed by joining selected dissimilar metals, such as aluminum alloy and brass.;Thermal mechanical analysis provided the prediction of the thermal and residual stress distribution in the welding joint. In the FSW modeling, instead of simulating the material flow phenomena occurring during the process, the properties of the FGM area were properly modified to account for time and space variations of the welded zone material properties; the subroutine USDFLD was applied for this purpose. Comparisons with existing models and experimental data also proved the validity of these proposed models. The FGM concept was used in modeling of the joint through a successive series of models with increasing complexity, starting from a 2D model with a stationary heat source and stationary FGM region to a 3D model with a moving source and FGM region varying in space and time.;An experimental campaign was initiated to validate the developed computational tools. A qualitatively good welding joint of A16061 and Brass260 was achieved by selecting the proper welding parameters including welding speed, rotational speed, and applying the appropriate pressure on the tool shoulder. Tension and hardness tests of the joints were conducted for the comparison with the base metals. The temperature along the welding line was measured with a non-contact method by using a commercial pyrometer. Because the surface of the welding joint was mixed with the two materials, a calibration of the pyrometer for the surface of this material was conducted before the FSW experiments. Finally, Energy Dispersive X-Ray (EDX) analysis was used to investigate the element distributions (Al, Cu, and Zn) of the welding joint.;In FSW, heat transfer plays an important role to the quality of the final welding joints. An in depth numerical investigation of the heat flows generated and transferred during this process was conducted in the FEM package ABAQUS. In the 2D simulations, the heat source generated by the friction between the tool shoulder and the surfaces of the workpieces was modeled as an equivalent heat flux. This distributed heat flux was loaded by using the user subroutine DFLUX in ABAQUS.