Deformation Behavior Of 2195 Al-Li Alloy Friction Stir Welding Sheet At Cryogenic Temperatures

The new generation of aluminum-lithium alloy has a relatively low density and high strength,which promotes the lightweight development of carrier rockets and effectively improves the carrying capacity of rockets.Therefore,it has a relatively wide application prospect in the field of arrow body materials.Because of al-li alloy overall forming thin-walled components with large size,difficult to forming large tonnage,billet size of equipment problem,this paper puts forward using friction stir welding(FSW)plank ultra-low temperature(196 ℃)forming method,combination of friction stir welding process with ultra-low temperature into forms,in the "forming" at the same time to ensure that the performance of the forming parts.In this paper,the mechanical properties and bulging properties of 2195 aluminum-lithium alloy FSW plate under ultra-low temperature(-196℃)were studied,and the influence of different deformation conditions on the coordinated deformation of FSW plate was explored,laying a theoretical foundation for practical engineering application.The mechanical properties of base material at different low temperature and heat treatment state were studied by unidirectional tensile test at ultra-low temperature.Then the mechanical properties of FSW sheet under different FSW parameters and different heat treatment conditions were studied.The results show that the welding speed has no great influence on the appearance morphology,elongation and strength of the welded joint,while the welding speed has great influence on the appearance morphology of the weld.Under the ultra-low temperature condition(-196℃),the elongation and strength of FSW plate are greatly improved.With the increase of heat treatment temperature,the strength of FSW plate is gradually increased,and the strength is all higher than the base material.The elongation increases first and then tends to be stable.By analyzing the coordinated deformation behavior under different deformation conditions under unidirectional stress state,the theoretical analytical model was established to explore the law of coordinated deformation of FSW plate.The results show that under the condition of-196 ℃ and unidirectional stress,the uniform deformation capacity of base material and welding plate is improved,and the strain distribution is more uniform.In the unidirectional stress state,the ratio of the thickness strain of the weld and the base material is mainly related to the strength ratio and thickness ratio of the weld and the base material.In the process of free dilation,it also depends on the position of the dilation zone,the closer to the top of the dilation zone,the greater the strain.By simulating the bulging process of FSW plate at ultra-low temperature(-196℃),the coordinated deformation behavior of FSW plate under different material and geometric properties was studied.When the strength of weld and base material is different,the deformation is mainly concentrated in the area with weak strength.The more uniform the performance of weld and base material is,the better the uniformity of plate deformation is.By thickening the weak area of FSW plate,the deformation uniformity of the plate can be improved.The position of weld is shifted from the center to the edge,the influence of weld on the deformation of FSW plate is weakened,and the ability of plate to coordinate deformation is improved.