| A7N01 aluminum alloy and friction stir welding are widely used in the frame,beam,end wall,beam and column of rail vehicle body.The structure of the tool will affect the flow behavior of the material and then determine the quality of the weld.Traditional research methods based on fluid mechanics cannot scientifically characterize the flow behavior of materials in the welding process in nature.Method of this article is based on solid mechanics,from the nature of the friction stir welding solid connection principle,build the multi-facets tool plastic simulation model of friction stir welding,discusses the multi-facets tool and frustum of a cone head of welding temperature field,the material flow behavior,the organization and the mechanical properties of weld joint the influence law of the effect of peace.In this paper,the main research contents include:(1)Based on the welding temperature field,furrow defects and the test results,as well as material migration,multi facets tool of friction stir welding of plastic science and accuracy of the simulation model validation has carried out.(2)The influence law of multi-facets tool on welding heat input and material flow behavior was studied.The welding heat input of the multi-facets tool is stronger than that of the circular tool,the time to enter the stable welding state is shorter,the effective welding seam is longer,the uniformity of the material flow and the mechanical properties of the welding seam are better than that of the circular tool,cavitation in the welding process is also more evenly distributed than that in the circular tool.(3)To explore the friction stir welding furrows and tunnel defects formation mechanism.The welding defects of the multi-facets tool are mostly half furrow-half tunnel type,and the defects of the circular tool are furrow-type,and the increase of welding speed will make the defects evolve into tunnel type defects.(4)The effect of heat input on the properties of welded joints was discussed.Increasing the welding heat input can improve the filling capacity of the material,but the abnormal growth of the microstructure grains induced by the high temperature should be prevented,which leads to the decrease of the weld strength.(5)The preventive measures of typical defects and welding process window are put forward.The matching degree of welding parameters determines the type of welding defects.Due to the extrusion of the facet,the three-facets tool can be adapted in low speed and high welding speed under the condition of no defect welding seam.The research results of this paper can provide theoretical basis for the structure and process design of multi-facets tool,and have certain guiding significance and application value for the popularization and application of friction stir welding technology. |
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