| The frictional coefficient about 2A12, 5A06, 7075-O and 7075-T6 four types of aluminum alloy was determined under different temperature through friction experiment. Based on the finite element software ANSYS, the friction stir welding temperature field was simulated with frictional coefficient, which changes along with the change of temperature. The temperature of four kinds of aluminum alloy FSW joint was measured by thermocouple temperature measurement system, then the comparative analysis of simulation results and measured results was given. The processing of friction stir welding about four aluminum alloy was carried out with the same processing parameters. Analysis of material frictional performance effect on temperature field in friction stir welding joint and weld formation.The friction test results show that the frictional coefficient between wrought aluminum alloy and H13 steel will experience three gradation along with the change of temperature. Firstly, the frictional coefficient decreases with the increase of temperature. Secondly, it will increases dramatically as the temperature continues to rise. Thirdly, the frictional coefficient begins to decrease from the maximum as temperature further increases, even reduces to zero approximately at 450 ℃.The friction and wear mechanism between aluminum alloy and H13 steel is also changed along with the variation of frictional coefficient, the friction mechanism changes from the dry friction to boundary friction, and the wear mechanism changes from abrasive wear to adhesive wear.Simulation results show that under the condition of the friction coefficient changing along with the change of temperature, 5A06 aluminum alloy can reach the highest temperature 501 ℃, then 7075-O and 7075-T6 reach the temperature 487 ℃ and 483 ℃ respectively, and the 2A12 aluminum alloy reach the lowest temperature 470 ℃. The aluminum alloy friction stir welding temperature is affected by the maximum of friction coefficient and the transition temperature of friction coefficient beginning to decrease. The greater the friction coefficient and the higher the transition temperature, the higher temperature the aluminum FSW joint can reach.The heating speed of four types of aluminum alloy in friction stir welding preheating stage is different. The changing trends of 7075-O and 7075-T6 aluminum alloy heating speed are similar, which remain unchanged after first increasing, then decrease as welding time passed. While the changing trends of 5A06 and 2A12 aluminum alloy heating speed are similar, which decrease after increasing as welding time passed. The heating speed in Aluminum FSW preheating stage is affected by initial fiction coefficient, transition temperature of fiction coefficient and the maximum of friction coefficient. The greater the initial friction coefficient, the lower the transition temperature and the greater the maximum, the higher heating speed friction stir welding can get in preheating stage.The results of weld formation show that the material fictional performance has an important influence on the weld surface morphology by affecting the weld surface temperature. When the sufficient heat production makes weld surface temperature exceed the melting point, part of the molten metal plays a role of lubrication in friction interface, which is helpful to get a good surface morphology. Welding nuclear size is affected by friction heat and plastic deformation resistance. When friction heat production is similar, the smaller the plastic deformation resistance, the greater the welding nuclear area and width. When plastic deformation resistance is similar, the greater the heat production, the greater the welding nuclear area and width. |
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