| Friction stir welding (FSW) was a solid-state joining process invented by TWI (The Welding Institute).It was called as green welding technology, because no feed materials and no pollution. It also has the excellent welding property working at lower temperature and easily automatic welding realization. FSW has been used at vast applications in the space flight apparatus,aviation production,shipbuilding,high speed train,natural gas packet,automotive industry. This new welding technique with uniqueness and superiority has been paid a great amount of attention by researchers ever since it was developed. This complicated process of Friction Stir Welding was made up of such four interactive factors as temperature variation, microstructure transformation, stress and strain and metal flow. So far, to proceed basic research in the temperature field,flow field,stress-strain field and their variation or interrelationship, that has become one of the important aspect in FSW researching and developing .There was complicated relationship between temperature field,flow field,force field during the friction stir welding process. In this paper,the finite element analyses and test were carried out for investigate the laws of evolution of fields and the influence of various parameters. Through the tensile experiment at High temperatures,friction coefficient experiment,shear strength of the welded material under elevated temperature and the measurement of heat and force, the influence and the relationship wre studied between the three dimensional field. The main works were done as follows:1. The simulation and real time testing of the dynamic temperature field were carried out, the influence laws were obtained: the temperature of advancing side lower than those of retreating side; the temperature graded distribution at near and front of friction stir tool were thicker than others; the figures of temperature distribution were gained in which thin plate corresponded to bowl, thick plate did to vase.2. The 3-D flow status was observation by using EDS(energy dispersive x-ray spectroscopy) of SEM(scanning electron microscope) and streamline visualization of thin sheet Cu placed into work piece by low amplifications microscope. To simulate the flow field, the RNG k-εmodel was selected. Also the flow field was numerically simulated by using software FLUENT. Plate cutting method the was used in order to observe the 3-D flow status at different depths. The results showed that: The shear characteristic phenomenon at advancing side but sufficient material plastically flow at retreating side, this because of the difference of the temperature; the material flow state can be influence by the various welding parameter, the rotation velocity influence more than others, but the rotation velocity too big may lead to the hole of weld; Onion rings structure in the cross-section was the most prominent feature which proved the metal sufficient plastic flow.3. As a new solid-state joining process, friction stir welding was complicated, in which three dimensional forces exhibits significantly key role. For detecting mechanical signals, self-designed experiment was designed. Using this system, real-time detection of the longitudinal force,the forward force and lateral force of the pin was implemented. The stress-strain field was simulated by the Deform-3D software. The results showed that: lateral force only occurred at the start-up stage welding; longitudinal force was the main factors impacting on the quality of welding; the notable factor influencing longitudinal force was the press in amounts. The power need in welding increased with welding speed increasing, but the various phenomena occurred, the power increase at first, reach the stabilization, then decrease with rotational speed increasing. And at direct measurement, we only found longitudinal force decrease with rotational speed increasing, variation range few with welding speed increasing, because the power in friction stir welding not only work by the friction force but also the shear stress.4. Because friction stir welding process was influenced and interacted by multi-field, the error of the simulations only selecting single field was bigger. The relationship among the fields was studied in order to closer the experimental results. Based the coupling method, the dynamical simulation was realized. Through the friction coefficient studying under elevated temperature detecting, the thermal-mechanical relationship was established; through the analyzing of the effect of deformation temperature and deformation rate on flow stress, the thermal-flow relationship was established; through the research of shear strength under different deformation condition, the mechanical-flow relationship was established.5. Friction stir welding was characterized by high weld quality, but welding defects still exist in the joints if unsuitable welding parameters were used. The common defects were analyzed, and the prediction were presented by the simulation basing coupling method.6. The longitudinal force was systematically tested by using the mutual affecting test, and the force data at different parameter. The experimental equations of longitudinal force are formulated according to the experimental data.
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