| Friction stir welding(FSW) is a new solid state joining method, which has the characteristics of environmental friendly, save energy and high quality, meet the requirement of modern welding. It is one of the most promising futures of welding technology. 2A12 aluminum alloy is a high strength aluminum alloy, has been widely used in aerospace, shipbuilding and other industrial fields. Due to poor weld ability, with fusion welding, the weld beads not only produce easily porosity, hot crack and large welding deformation et al, but also softened seriously, restricts the further application in modern industry. Friction stir welding provides a new idea for effective connection of 2A12 aluminum alloy.The welding experiments on 2A12 aluminum alloy plates of thickness 6 mm was performed with friction stir welding, studied effects of the welding speed, rotation speed and press amount on quality of the welded joint. When welding parameters were appropriate, the weld bead with excellent surface quality, no internal defects and good quality could be obtained. The results of mechanical property test show that the tensile strength of joints can reach 371.2 MPa, which is 87.3% of base metal, and elongation rate is 6 %;The strain fracture appears at the advance side of joints, the fracture belong to the ductile fracture; The refined and equiaxed grains whose size is much smaller than that of base metal(BM) formed in weld nugget zone(WNZ), the deformed grains are formed in thermo-mechanically affected zone(TMAZ),coarse grains are formed in heat affected zone(HAZ); The welded joint indicated softened zone during welding process; The distribution of micro-hardness of joint belonged to ―W‖ type, the lowest hardness is in TMAZ of advancing side; The microstructure features and properties of the different parts of joint are related to different thermal and mechanical combined actions which have been experienced in the welding process.On the basis of friction stir welding experiments, a finite element model is developed to analyze the FSW thermal process, which considers the effect of the material flow velocity difference between the advancing side and the retreating side on the welding process. The software package ANSYS is used to conduct numerical simulation of the FSW process of 2A12 aluminum alloy. The dynamic evolution of temperature field and characteristics of weld thermal cycles on the test plates were studied. The effects of the welding speed, rotation speed, shoulder’s radius, stir pin’s radius on temperature field distribution of the welding process was analyzed. The results showed that with increase of welding speed the heat input decrease, workpiece temperature drop, the trend of weld temperature asymmetry distribution is more obvious; When the rotation speed increases, the workpiece temperature increase, it’s effective to improve temperature at the bottom of the weld, but it has no effect on the asymmetry of temperature field distribution; With the shoulder’s radius increases, the friction heat increase, the temperature of workpiece remarkable increase, but temperature difference of the top surface between bottom surface increase. When the stir pin’s radius increases, the temperature of the central and below area on the weld cross section change obviously, the temperature difference of top surface between bottom surface of workpiece decreases. The results of numerical simulation provide reference data for the optimization of friction stir welding of 2A12 aluminum alloy. |
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