Numerical Simulation Study On Friction Stir Welding Process Of 7075 High Strength Aluminum Alloy

In recent years,7075 aluminum alloys have been more and more widely used due to their high strength and low density,but it is difficult to weld them.As a new type of solid-state joining technology,friction stir welding has been widely used in the aluminum alloys.However,the traditional experimental method is not only labor-intensive,but also difficult to display the overall temperature distribution of the weld,nor can it visualize the speed of the material.Therefore,based on the finite element numerical simulation technology,the numerical simulation of temperature field and flow field in the friction stir welding process is carried out for the 7075 aluminum alloy.Based on the theory of fluid dynamics,FLUENT,a type of fluid simulation software,was used to study the temperature field and flow flow field in the process of friction stir welding for the 7075 aluminum alloy.The effects of stirring head speed,welding speed and stirring head taper on temperature field and flow field were studied.The simulation results were verified by thermocouple temperature measurement experiments and marker embedding experiments.Combining the temperature field and velocity field analysis to predict the quality of the weld,a set of optimal process parameters for welding 7075 aluminum alloy was explored.The main results obtained in this article are:(1)The temperature field simulated by the distributed surface heat source model shows that the temperature on both sides of the weld is asymmetrically distributed.The temperature on the advancing side is higher than the receding side.The temperature of the weld cross section is funnel-shaped.The highest temperature of the workpiece appears on the shoulder edge.The simulation results of different welding parameters show that the higher the rotation speed of the spinning tool,the higher the workpiece temperature.The higher the welding speed,the lower the temperature of the workpiece.The accuracy of the temperature field simulation results under different welding parameters was verified by thermocouple temperature measurement experiments.In addition,for different taper needles,the smaller the taper,the higher the temperature of the workpiece.(2)The simulation results of the velocity field show that the velocity of the material on both sides of the weld is obviously asymmetric when the welding is steady.and the speed on the retreating side is higher than that on the advancing side.According to the streamline diagram,we can see that the material on the retreating side bypasses the spinning tool from the front of the welding to the rear of the welding,and then flows to the advancing side,where the welding zone is forming.This conclusion was verified by the mark embedding experiment.The simulation results of different welding parameters show that the higher the stirring head speed,the faster the material flow rate.The welding speed has little effect on the material flow rate.However,the smaller the welding speed,the closer the welding position of the material is to the welding center line.(3)Considering the influence of welding parameters and the taper of tool pin on the temperature field and flow field,a set of optimal welding process parameters for welding 7075 aluminum alloy had been explored.When the rotation speed is 800r/min,the welding speed is 100mm/min,and the taper of the tool pin is 0.33,the performance of the weld will be best.