The Research Of Aluminum Alloy Friction Stir Welding Thermal Action

The welding torque under different process parameters is measured by the torquemeasuring system. During the welding process, the production of thermal power and thethermal inputs are calculated. What’s more, the temperature field distribution of the stir tooland the test plate is simulated and measured separately by the finite element softwareABAQUS/Standard and the self-made temperature measuring system. As a result, thefriction stir welding thermal process is studied comprehensively and systematically.Results show that under a certain welding speed, the numerical relations between thetorque and the rotation speed can be described by an exponential function model. With theincrease of rotation speed, the torque decreases according to a certain rule. When therotation speed increases to a certain degree, the torque remains constant while the heatproduction power, heat input power and peak temperature of the weld joint keep increasing.The torque is determined by welding temperature and the stirring head features.The temperature curves of the friction tool show that during the forward process, thetemperature field of the friction tool can be thought as a quasi-steady state temperaturefield. The heat that flows into the friction tool and flows out of the friction tool keeps adynamic balance. The heat that flows into the friction tool only makes up a small part ofthe whole heat input, which indicates that the friction stir welding process has a highthermal efficiency. During the friction stir welding process, the heat that distributes alongthe axis of the tool is a one-dimensional heat conduction.Under different boundary conditions, the temperature field of welding test plate showsthat with the increase of the shoulder diameter, the rotation speed or the down quantity andthe decrease of the welding speed, the temperature of each measured point increases. Theshape of the friction pin also has an effect on the temperature field. When use a threadedstirring pin to weld the test plate, the temperature is slightly lower than using a cylindricalone. During the welding process, the backing plate which has worse thermal conductivitycan significantly improve the temperature of weld joints, while the backing plate which hasbetter thermal conductivity can lead to the decrease of the temperature of weld joints,especially the temperature of the bottom of test plate, which contributes to the incompletejoint penetration defects on the back and so on. The distribution of the temperature of the friction stir welding can be described fromthe numerical simulation. As the stirring tool moves forward, the high temperatureisothermal surface becomes larger, and the front test plate presents a larger temperaturegradient, while the temperature of the back test plate changes more slightly, which presentsa less temperature gradient. Along the thickness direction, the highest temperature appearsin the near surface area below the shoulder. The shape of the high temperature zone is justlike a bowl, which is similar to the weld joints after the welding process.The rotation speedonly affects the amount of heat input, while it has no influence on the trend of temperaturechanging. With the increase of the rotation speed, the temperature increases in a nonlinearproportion.