Study On The Stationary Behavior Of The Severe Plastic Deformation System And Analytical Models For Friction Stir Welding

Friction stir welding(FSW)as a high efficiency solid-state joining technology plays an irreplaceable role to meet the high-strength aerospace aluminum alloys requirements of light weight,high performance and high service performance.However,most current researches are only focused on specific FSW of aluminum alloy,ignoring the systematic study on the common feature of friction welding--the evolution process of severe plastic deformation system and its characterization parameters.Therefore,this study takes thin-wall tube aluminum alloy 2024,7050 and thin-wall tube W18Cr4 V respectively,and the method of combining experimental research with analytical model was adopted.The general laws under the steady state system of severe plastic deformation system was studied,and analytical model of in plastic flow stage and severe plastic deformation system of FSW,and tensile strength analytical model of joints of severe plastic deformation system of FSW was established.The research results provide theoretical guidance for the optimization of FSW process parameters.The main research results are as follows.Under constant pressure friction,the formation of severe plastic deformation system with homogeneous or heterogeneous combinations must reach the stage of plastic flow.The response of peak friction coefficient and the time to reach the peak friction coefficient is more significant.On the contrary,the rotational speed is not the key factor affecting the friction coefficient in the stable stage.Based on the above experimental,combining the fluid control equations and material constitutive equation is established under the condition of constant pressure homogeneous equipping severe plastic deformation system of viscoplastic flow peak temperature and the steady state analytical model of the welding power,and by using experimental results validate that the model has certain accuracy and reliability.Based on the analytical model in the viscoplastic flow stage of severe plastic deformation system,the boundary condition is the Campbell stability criterion in the field of plastic deformation.Based on reasonable assumptions,inverse hyperbolic sinusoidal constitutive equation and governing equation of fluid dynamics,and with strain rate sensitivity coefficient as the intermediate variable,the mathematical relationship between the severe plastic deformation system and the process parameters of FSW was established.The calculate results show that the error band is within 5%,which strongly supports the accuracy and universality of analytical model for severe plastic deformation system of FSW.Based on the experimental results of FSW AA5083 aluminum alloy butt joint under different process parameters,the analytical model of tensile strength of FSW severe plastic deformation system joint was established by dimensional analysis method.And accuracy of the model is verified by experiments,and the model is proved to be correct within 5%.The results show that the welding heat input of the optimal processing window is between ω/v=4-5 rev/mm,The causes of welding defects were analyzed with severe plastic deformation system of analytical model for peak temperature,and the rationality of guiding the selection and optimization of process parameters through this analytical model was proved.