| With the development of car safety and lightweight,high-strength steel and aluminum alloys are increasingly used in automobile production,the hybrid application of steel and aluminum makes joining technology the key to solve material applications.However,due to the difference in thermal physical and chemical properties of steel and aluminum,the traditional riveting technology has low joint strength and poor joint appearance;while the fusion welding technique easily produces a large amount of brittle hard intermetallic compounds in the joint,and the joint is prone to crack.As a kind of solid phase welding technology,the friction stir welding technology studied in this paper can weld sheet at low input state,and the joint strength is high,which can effectively control the production of metal compounds in the welding process,It is of great significance to solve connection problem of high strength steel and aluminum alloy in the automobile manufacturing.Firstly,according to the heat generation characteristics of the friction stir welding in this paper,DP590 steel and AA6061-T6 aluminum alloy sheet were taken as the research object,and the heat source mathematical model of steel and aluminum friction stir welding was established,and which was compiled into DFLUX heat source subroutine in the next step.The mixed friction state of the adhesion and slip between strring and sheet was considered in the heat source,and the difference in the yield shear strength of the DP590 steel and the AA6061-T6 aluminum alloy and the difference in the friction between the stirring head and sheets was considered.Secondly,the friction stir welding heat transfer model of steel and aluminum dissimilar metal butt joint is established by using ABAQUS software with combined with DFLUX mobile heat source subroutine,the distribution law of temperature field in welding process is studied,The rationality of the model is verified by comparing with the relevant literature.The influence of different offset positions of the stirring head on the joint temperature field is studied by adjusting the relative position of heat source and sheet.The effects of stirring speed and welding speed on the temperature field are studied by adjusting the heat source parameters.The degree of influence of the preheating time,the stirring head speed and the degree of influence of the welding speed on the temperature field was comprehensively compared.The results show that the highest temperature in the welding process is located on the side of DP590 steel sheet;The bias of the stirring pin mainly affects the temperature distribution of the steel sheet.The rotation speed is the main factor affecting the temperature field of the welded joint.Thirdly,the stress field model of friction stir welding is established.The residual stress distribution and deformation characteristics of friction stir welding joints of DP590 steel and A6061-T6 aluminum alloy are studied,the rationality of the model by comparing it with the relevant literature was verify.The influence of the position of the strring head on the residual stress of the joint and the deformation after welding was analyzed.The influence of the rotating speed and welding speed on the residual stress and deformation of the joint was studied by using the temperature field under the corresponding heat source parameters.The results show that the deformation of aluminum sheet is larger than that of the steel sheet;the position of the mixing head mainly affects the residual stress distribution on the steel sheet;but the influence on the aluminum sheet is not obvious;the larger residual stress and the more obvious deformation of joint when the higher rotation speed of strring head and the smaller welding speed;uneven heat transfer between steel and aluminum is the main reason why the influence of welding parameters on residual stress is different from that of the same metal.Finally,the model of steel and aluminum friction stir welding flow field is established,the flow law of metal is studied.The results show that the metal fluidity on the sheet surface is the strongest in the shoulder area;The mixture of steel and aluminum appears on the receding side under the action of the side of stirring needle,and the mixing range is not obvious;the metal flow intensity is low and the mixing range of steel and aluminium is small in the action area of the bottom of stirring needle. |
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