Study On The Design Of Multi-flat FSW Tool And Its Effect On Joint Structure And Properties

The FSW tool is an important part of the friction stir welding process,and is an important factor that determines the quality of the weld joint.At present,the trial and error method is often used for the design of the FSW tool,which not only lacks systematic and theoretical support but also wastes a lot of manpower and material resources.In view of this,based on theoretical derivation,this paper scientifically constructed a multi-flat tool heat generation model,which can effectively numerically simulate the temperature field and flow field during the welding process of the multi-flat tool.The influence of the number of flats on the welding temperature field,the structure of the welded joints and the mechanical properties is discussed.The main research contents of this article include:Multi-flat tools heat source model.Based on the heat generation principle of friction stir welding and the structural of the tool,a multi-flat stirring head heat generation model was constructed.Through the welding quick stop method,the flat equivalent contact state variable was analyzed and determined.A heat-flow coupling model of FSW in steady state welding process was established,and the validity of the model was verified by using the tracer method.The simulation results show that when the plane equivalent contact state variable is 0.85,the simulation results of the multi-plane stirring head are in good agreement with the temperature and flow fields of the welding experiment.The influence of the number of tool flats on the temperature field,pressure field and flow field of the welded joint.The T_max of the multi-flat tool is higher than that of the conical tool,and as the number of planes increases,T_max shows an upward trend.The pressure field of the multi-flat tool/workpiece interface is significantly greater than that of the conical tool,and as the number of flat increases,the interface pressure decreases.The flat changes the flow direction of the material around the tool,causing some materials to move horizontally.The influence of the number of tool flats on the structure of welded joints.The microstructure analysis of the joints shows that the joints of the conical tool,tri-flat tool and quad-flat tool all show that the average size of the upper layer grains is larger than that of the middle and bottom,under the same cross section,the tri-flat tool welding nugget zone has the smallest grains.In this paper,the existence of flats strengthens the squeezing effect of the stirring head on the material and reduces the grain size in the weld nugget,but as the number of flats increases,the squeezing effect of the stirring head on the material gradually weakens.The influence of the number of tool flats on the performance of welded joints.The stratified test results of the joint performance show that the microhardness of the three types of stir welded joints are U-shaped,and the hardness value of the upper layer is the lowest,which is the weak area that affects the performance of the welded joint.On the same horizontal plane,the microhardness value of the tri-flat tool is the highest.The mechanical properties are the best.The tensile strength is 413MPa,which is 90%of the base material.As the number of planes increases,the tensile strength of the welded joints shows a downward trend.In summary,this article has conducted in-depth research on the establishment of a multi-flat FSW tool heat generation model,the number of tool flats and the principle of action.Important theoretical significance and practical value of engineering.