Fundamental Research On Meso Friction Stir Joining Of Aeronautical Aluminum Alloy

With the continuous development of our country's aerospace industry,the manufacturing technology in this field gets rapid development.In order to save energy and reduce costs during the manufacturing process of unmanned aircraft,satellites,rockets,supporting facilities along the high-speed railway,lightweight structure has become an important direction of the design and manufacture which generates new requirements for thickness of plate and connection technology.For sheet metal and specific processing parts,narrow seams are required.However,the traditional melting connection method and riveting method cannot meet the requirements of the structure manufacturing of these industrial products and improvements should be made on the basis of traditional friction stir joining.This research project,combining the numerical simulation with the method of experimental research,solves the problem of friction stir joining for aluminum alloy plates with thickness of 1mm and below.The main work finished and main results achieved in this research project are as follows:(1)Study on simulation during the process meso friction stir joiningThe MFSJ heat source model was established,through the shoulder radius calculated the relationship between the width and the input heat;It was found that there was insufficient heat input at normal temperature,and the peak temperature could not meet the requirements while heat input could be increased by preheating;The temperature field,flow field and stress field of 6061 aluminum alloy plate with a thickness of 1mm were simulated by finite element software ANSYS and it was found that temperature field smear under MFSJ was more obvious;By analyzing the influence of speed and feed speed on the peak temperature,Flow field flow was in different ways from top to bottom,after preheating,with higher fluidity,the metal in connection area was thermo plasticized.The molding of the material mainly depended on the lower pressure of the shaft shoulder.Under the joint action of the workbench,the plastic metal was extruded into shape.(2)The development of meso friction stir joining equipment(MFSJ)A MFSJ device was designed and manufactured for connection of thin plates.The connecting material was aluminum alloy and the plate thickness was less than 1mm.The requirements of the equipment were analyzed and the main structure was designed,including the design of auxiliary heating system and control system;The simulation of temperature field and stress field of theequipment was carried out,and the vibration performance and machining accuracy were tested.(3)Study on the process of meso friction stir joiningThe MFSJ process parameters of plates with different thickness less than 1mm were preliminarily obtained,and the surface arcs were found to be different from that of an ordinary friction stir joining;The characteristics of surface arcs under high speed were analyzed by Matlab,Through a large number of basic process,the machining difficulty of different materials is obtained,and the actual size of the shaft shoulder under unheated condition is verified,and the law of speed and surface appearance was obtained;Under preheating condition and normal temperature condition,the experimental data of MFSJ were compared,and it was found that the surface of the connection area was smoother under the auxiliary heating condition,and the tensile strength was higher;Finally,the optimized process parameter combination was obtained through orthogonal process.(4)Study on the acting force of meso friction stir joiningAccording to the test results of the acting force,the acting force formula of longitudinal,transverse and axial forces was fitted;Through the analysis of the test results of the force,it was found that the periodic change rule was only related to the speed of stirring head,rather than the feed speed,the connection material and the thickness of the material;Increasing the preheating temperature would reduce the axial force,but it had no effect on the cyclic variation of axial force.(5)Microstructure and performance evaluation of meso friction stir joiningMicrostructure observation,electrochemical corrosion and tensile properties,bending performance,wear performance and vickers hardness were evaluated to the optimized MFSJ connection area;Comparing the performance between the experimental plate and base metal,analyzing the changes in various performance of MFSJ under preheating condition,it was found that after preheating,all the performance properties of the plate connection area were close to or better than the base metal,the mechanical properties of the connection area significantly improved compared to that at normal temperature.