| In the automotive field,lightweight design is a good way to solve the problem of insufficient renewable energy.The use of lighter aluminum alloy instead of steel has become the focus of research in the field of automotive lightweight in recent years.However,due to the low melting point and easy oxidation of aluminum alloys,the quality of the welding points formed by traditional fusion welding is poor,and friction stir welding as a solid phase welding technology perfectly overcomes the defects generated by the recrystallization process in fusion welding.However,at this stage,there is a lack of a transient heat input model that can accurately describe the whole process of friction stir spot welding.Therefore,based on the whole process of friction stir spot welding,a new transient input heat source model is established.This model is used to characterize the internal relationship between welding parameters and welding spot formation,and the reliability of the model is verified by friction stir spot welding experiment.The aim is to clarify the temperature field changes during the welding process,explore the forming mechanism of the solder joints and optimize the welding process and mechanical properties of the solder joints.The details are as follows:First,based on the whole process of friction stir spot welding,a new transient input heat source model is established.By determining the basic assumptions such as friction assumption and yield criterion,the heat generation power equations of each part of the stirring pin are obtained,and the action logic of the uniformly distributed surface heat source and the double ellipsoid heat source is determined in conjunction with the actual welding conditions,and a point for friction stir spot welding The new transient input heat source model in three stages of depressing,staying and cooling,combined with secondary development,realized the simulation of the welding process.Secondly,this paper conducted friction stir welding experiments to provide a basis for the accuracy of the simulation model.Select the 60mm-T6 aluminum alloy sheet 2mm thick commonly used in passenger cars,and match the appropriate size of the stirring head.Perform the experiment according to the experimental requirements measured by the welding thermal cycle curve,and at the same time extract the relationship between the temperature at the observation point and the time.The results show that the prediction results obtained by the simulation calculation are in good agreement with the actual situation,and the reliability of the model is verified.Finally,this paper studies the influence of welding parameters on the change of welding temperature field.The four factors of boundary conditions,stirring head speed,shaft shoulder size and stirring head pressure were investigated using single factor analysis method.Among them,the stirring head speed and shaft shoulder size have a high correlation with the peak temperature characteristics.The boundary The conditions and the pressure of the stirring head have a great influence on the temperature field distribution.The research on the temperature field of the whole process of friction stir spot welding aims to clarify the welding spot forming process,provide support for the subsequent exploration of the residual stress of the formed weld spot and optimize the mechanical properties of the weld spot,and provide the basis and basis for friction stir welding as solid phase welding Mechanism analysis. |
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