Research On Friction Stir Weld Joining EHV Transmission Pipeline

Compared with the traditional ground overhead transmission,The underground aluminum alloy EHV transmission pipeline has the advantages of safety,reliability and larger transmission capacity,which is the main development trend of long-term transmission projects in the future.However,the high-quality manufacturing technology of this kind of pipeline is not mature and perfect at present.FSW technology has significant advantages in connecting aluminum alloy.Therefore,this paper studies the technology of large diameter ultra-high voltage aluminum alloy transmission pipeline connected by friction stir welding.Since the thickness of the pipe wall is up to 30 mm,this paper adopts the double-sided friction stir welding scheme and the single-sided welding thickness is 16 mm.The main research work and achievements of this paper are as follows:(1)The FSW heat source model verified by most scholars was used to simulate the temperature field of welding 16 mm thick 6061-T6 aluminum alloy,and the range of parameters of FSW was determined.The results show that the tool with a 24 mm shoulder can form a good weld joint under the parameters of rotating speed of 500 rpm and above and feed speed of 150 mm/min and below.(2)Based on the simulation of temperature field,the thermal mechanical coupling simulation is carried out,and the distribution of residual stress after welding is obtained,which is compared with the measured value.According to the simulation results,the longitudinal residual stress on the surface after welding presents a double peak distribution,the peak value appears at the two sides of the weld about 1 times of the shoulder diameter from the weld center,the transverse residual stress presents a single convex distribution,and the peak value is near the weld.(3)Base on the simulation results of FSW temperature field,a method is proposed to quickly estimate the critical value of the diameter of the shoulder according to the material and thickness of the parts to be welded.Calculation results of this method shows that the diameter of the tool shoulder is at least 20 mm when welding the 16 mm thick 6061-T6 aluminum alloy.(4)According to the above research results,the friction stir welding experiments of 60 groups of 6061-T6 aluminum alloy with 30 mm thickness were carried out,and the tensile test of the weld was be done.The results show that the best parameters of FSW are: the diameter of the shoulder is 24 mm,the rotating speed is 650 rpm,and the feed speed is 100mm/min.the tensile strength of the best weld is 80% of the base metal.Finally,the microstructure,hardness and residual stress of the weld under the optimum process parameters were be analyzed.