| The 20 mm thick plates of 2024-T4 aluminum alloy were welded by friction stir welding with six pins and external heat source equipment. The effect of the pin’s shape on the temperature of weld joint was investigated. The size of the nugget zone was measured. The influence of shape of the pins on the plastic metal flow behavior was analyzed. The temperature field under different initial temperature was simulated by ANSYS. The influence of regularity of temperature field on the plastic metal flow was studied. These can provide a theoretical reference for the design of the pins and the welding of thick aluminum alloys.The result shows that, the range of suitable welding parameters for friction stir welding of 20 mm 2024 aluminum is narrow. The influence of welding heat input on the weld formation of the thick aluminum is significant. The defect-free weld joint can be obtained when the welding speed is 37.5mm/min and the rotation speed is 375r/min.The influence of the pin shapes on the flow of plastic metal is great. The flow amount of weld plastic metal can be promoted adequately if reducing the pin taper from 25°to 15°. That is, when the taper is reduced to 15°, the flowing driving force for the plastic metal came from the surface thread of the pin become smaller. However, with the end diameter of pin increasing, the friction area is increased, and then the heat output is increased. This will make the high temperature zone at the bottom of the joint broader, and the amount of the plastic metal in the weld and the pin increased, then the extrusion pressure of plastic metal in nugget to the surrounding metal at the tip of the pin become strong. Thus, the height, width and area of nugget become greater.The flow of the weld plastic metal was enhanced by using pin with multiple threads on it surface. When the thread number of pin is three, compared to one and two threads, the channel for plastic metal flow are increased, the phenomenon of sucking-extruding of the plastic metal in the axial direction of the pin is more prominent, so that the amount of hot plastic metal divorced from the end of pin is increased. But the temperature of base metal around the nugget does not change. In other words, no matter how many thread number of pin is, the deformation resisting capability of base metal around the pin is same. Therefore, with the amount of plastic metal increasing, the expansion of metal in nugget toward weld surface is enhanced, welding defect, such as holes, is reduced.Holes defect in weld is eliminated and defect-free weld joint can be obtained if 2024-T4 aluminum alloy is weld under appropriate external heat source temperature. When the temperature of external heat source is 40℃, the overall temperature of 2024-T4 aluminum alloy weld increases, therefore, the high temperature zone of the joint will be broader, and the softening degree of the metal and the amount of plastic metal will increase. Meanwhile, the amount of metal flowing toward the bottom of the weld and the extrusion pressure of nugget metal increases, the resistance to the expanded nugget is reduced. The sucking-extruding phenomenon will be more prominent, the flow tendency of plastic metal in the transverse direction is enhanced, and the potential energy of the plastic metal for axial movement is reduced. Thus, the height, width and area of the nugget will become larger. |
PDF Full Text Request