Research On Lightweight Friction Stir Welding Equipment And Technology Of Thin Plate Aluminum Alloy

For the problems in the conventional friction stir welding of thin-walled aluminum alloys,such as the large axial force,serious thinning and wide heat-affected zone,etc.,this paper establishes the research task of thin-aluminum alloy lightweight friction stir welding equipment and technology.The principle and composition of friction stir welding equipment for thin plate aluminum alloys are described in this paper.On the basis of the completion of the development of the welding experiment platform,the 3003 and 6061 aluminum alloys were used for test welding.The results show that the equipment has the advantages of high rotation speed,small volume,small welding axial force,etc.It can effectively achieve the docking test of 1 mm,2 mm 3003 and 6061 aluminum alloy plates,and basically meet the requirements of lightweight friction stir welding of thin plate aluminum alloy It lays the foundation for the follow-up welding process optimization and the law’s exploration.The mechanical parts of the welding equipment include the static gantry doors of the casting structure,the X,Y,Z directional screw and slide rails,and the plane force measuring table.The electrical parts mainly include: three-dimensional digital motion control systems,programmable controllers,and infrared Temperature sensor,high-speed spindle and its driver,plane force sensor,axial force detection,force signal acquisition system.The outstanding advantages of this equipment are high rotation speed,small volume and small axial force required.It can detect the axial force,forward resistance and lateral force of the friction stir head,and the temperature change of the set point of the welding area around the mixing head.For the butt test of a 300 mm aluminum alloy sheet with a thickness of 1 mm,the optimum process parameters were a rotational speed of 11,000 rpm and a welding speed of 1000 mm/min.In the preheating phase and the finishing phase,the friction resistance of the friction stir head is not more than 50N;in the welding process,it is usually not more than 300 N,and it increases with the welding speed.Through the fracture analysis of the weld joint,it was found that the fracture of the joint was ductile fracture,but the tensile strength and hardness had decreased.The reason was that the strengthened form of 3003 aluminum alloy was cold work hardening,and the welding heat effect resulted in the cold hardening effect of the joint part eliminate.Through electrochemical corrosion tests,it was found that the corrosion resistance of the 3003 aluminum alloy after a high-speed friction stir welding was slightly reduced.This is mainly because the high-speed stirring action destroyed the original microstructure.For the butt welding test of 1 mm thick 6061 aluminum alloy,the best welding parameters are: rotation speed 10000 rpm,welding speed 300 mm/min,welding joints obtained by welding using this process parameter have small deformation,no welding defects such as tunnels,cracks,etc..The tensile strength of the welded joints reached 87.2% of the base metal,and the hardness reached 72.7% of that of the base metal.Through observing the microstructure,6061 aluminum alloy was found after high-speed friction stir welding,and the weld zone and heat affected zone were organized.All have undergone significant changes,the grain size of the weld zone has been clearly refined,and the grains in the heat-affected zone have grown slightly.Through electrochemical corrosion tests,it has been found that the 6061 aluminum alloy has improved corrosion resistance after high-speed friction stir welding.It is due to the refinement of the grain size of the weld nugget,the more even distribution of the size of the weld nuclei,and the more diffuse distribution of the precipitated phases,which results in a decrease in the propensity of microscopic corrosion of the surface of the weld nuclei.Tests have proved that: high-speed friction stir welding can quickly and effectively complete the welding of 6061 aluminum alloy,obtaining good mechanical properties of welded joints,while ensuring that the microstructure of heat-affected zone is better.