Numerical Simulation And Experimental Investigation On Temperature And Materialsflow Fields In Friction Stir Welding Of Aluminum Alloy

The research on friction stir welding of 6061-T6 aluminum alloy via numerical simulation and experimental method was performed in the present dissertation. The investigation contents include the heat generation, temperature distribution, materials flow, dissimilar welding of 6061-T6 aluminum alloy to pure copper, the improvement of the friction stir welding and the numerical modeling for the modified welding process.At first, a modified three-dimensional model was established to simulate the friction stir welding of the 6061-T6 aluminum alloy. A detailed calculating method of the heat generation was proposed by taking account of the contact conditions between the tool and the work-piece. During the friction stir welding, the welding temperature and materials flow behaviors were monitored by thermocouple and marker material, respectively. The results show that the heat mainly generated within the region near the shoulder, the high temperature exists within the upper portion of the weld and decreases along the thickness direction. The strong material flow mainly occurs within the region near the tool and the material ahead of the tool sweeps toward the retreating side and finally deposits behind the tool. During this procedure the material is extruded to experience different shear orientations, and a defect-prone region exists in the region where material flow is weak. The temperature field and material flow behaviors predicted by the simulation method are in good agreement with the results obtained by the experiments.Secondly, the dissimilar friction stir lap welding of 6061-T6 aluminum alloy to pure copper was investigated. In the present research, due to the fact that the formation and growth of the intermetallic are significantly controlled by the thermal history, the underwater friction stir welding was employed for fabricating the weld, and the underwater weld was analyzed via comparing with the weld obtained under same parameters by classical weld. The results show that the water could decrease the peak temperature and shorten the thermal cycle time, and the amount of the intermetallic in the underwater weld is obvious less than in the classical weld, the Al-Cu diffusion interlayer at the Al-Cu interface of the underwater weld was obviously thinner than that of the classical weld, the grain size of the two materials in the underwater weld was smaller than that in the classical weld.Thirdly, a two-dimensional model, in which the vaporization of the water was considered, was developed for the underwater friction stir welding of 6061-T6 aluminum alloy. The character of the temperature distribution was studied by the numerical simulation and experimental measure. It is found that the temperature field predicted by the simulation method is in good agreement with the results measured by the experiment. The results show that the temperature would reach the peak value after about 2.5s during the dwell period, and the mechanical perporities of the weld were improved.