Analysis Of Temperature And Residual Stress In Ultrasonic Friction Stir Welding Of Aluminum Alloy

Aluminum alloy has the advantages of small density and high specific strength,and is an important material for key components of rail trains.These parts are mainly connected by welding.Ultrasonic friction stir welding is widely used due to its advantages of low welding temperature and high joint strength.During the welding process,the welding temperature and residual stress after welding will affect the quality of the weld.Therefore,this article considers the combined effect of friction stir and ultrasonic vibration energy to establish a numerical model of ultrasonic friction stir welding to analyze temperature and residual stress.We design experiments to verify the model,and use the established model to analyze the parameters of temperature and residual stress.The main work and results of this article are as follow:(1)Considering the effect of ultrasonic vibration on the pressure under the shaft shoulder,the material constitutive model and the friction coefficient,the thermo mechanical substitution method and the sequential supplement method were established.The temperature of the workpiece surface during the welding process is measured by experiments to verify the accuracy of the model.It is simulated that the high-temperature area is located below the stirring head during the welding process,and spreads in a ring shape to the surroundings.The peak temperature is located in the area on the forward side.The test shows that the temperature fields on both sides of the weld are asymmetrically distributed,and the temperature on the advancing side is higher than the temperature on the retreating side.The simulation results are basically consistent with the test results,the error is about 0.6%(2)Numerical simulation of 7075 aluminum alloy is sheet by sequential coupling method.The temperature result of ultrasonic friction stir welding is loaded as a thermal load in the residual stress model to simulate the residual stress after welding.The simulated residual stress after welding is mainly longitudinal stress,and the longitudinal residual stress is distributed in an "M" shape in the direction of the vertical weld,and the lateral stress value is relatively small.Tensile stress appears in the weld area,and compressive stress appears away from the weld.(3)The article uses established numerical model to analyze the influence of different parameters on the welding temperature and residual stress.When the other parameters remain unchanged,the welding temperature increases with the diameter of the shoulder,increases with the length of the stirring pin,increases with the speed of the stirring head.The welding temperature decreases with increasing welding speed,decreases with increasing ultrasonic amplitude,and decreases with increasing ultrasonic frequency.When the other parametersremain unchanged,the residual stress increases with the diameter of the shoulder,increases with the length of the stirring pin,increases with the speed of the stirring head,increases with the welding speed.The residual stress decreases with increasing ultrasonic amplitude,and decreases with increasing ultrasonic frequency.