Formation And Mechanical Properties Of Friction Stir Additive Manufactured 2195 Al-Li Alloy

As our country accelerates its construction of manufacturing powerful country,achieving large application of lightweight?high-performance and functional materials has become a common goal in many fields such as aerospace,automobile manufacturing,and power electronics industries.Due to its excellent welding performance and corrosion resistance,2195 aluminum alloy has been widely used in the manufacture of large-scale launching vehicle fuel tanks.Traditional processing methods(forging or casting)have many difficulties when manufacturing larger structural parts such as complex processing and high cost.Chemical milling and mechanical milling technologies require higher equipment capabilities and technological levels with many problems like low efficiency?high cost ? poor accuracy and large deformation,design requirements cannot be guaranteed.In order to solve the above problems,this paper proposes friction stir additive manufacturing self-constrainted technique(FAST)based on friction stir welding(FSW),using a welding tool assembled by stirring pin with features of thread and three milling facets and self-constrained stationary shoulder to conduct the research of FAST.In this paper,FASTis used to conduct single-layer and multi-layer experiments,and the mechanical properties and corrosion resistance of the samples are studied,realizing the optimization design of the welding process.In this paper,the processing feasibility of FASThas been explored,high-quality joints have been successfully obtained.Part of the precipitation phase near the additive manufacturing zone is dissolved into the matrix,part of the precipitation phase iso found to grow up.The precipitate phase in the WNZ is sufficiently stirred and broken into extremely fine particles,the number of precipitate phases is larger.The compression shear test of the joints shows the following conclusions.As the traveling speed increases while the rotational speed remains unchanged within a certain range,the joint bearing capacity increases.As the rotational speed increases while the travel speed remains unchanged within a certain range the joint bearing capacity decreases.The hardness test shows that the hardness of the additive manufacturing zone is higher than that of the BM.As the welding speed increases,the microhardness of the joint increases.In the end,the best quality joint is obtained under the process parameters of 800 rpm and 200 mm/min.The friction stir additive manufacturing process is optimized,multilayer additive joints are fabricated.The results show that the additive joint fabricated under the process parameters of 200 mm/min and 800 rpm is the best multilayer additive joint.The distribution of the multi-layer additive structure is similar to the single-layer structure.Since the lower layer undergoes more thermal cycles and mechanical stirring processes,the lower layer has a smaller grain structure than the upper layer,but the lower layer has less second phase contents than the upper layer.Compared with the single layer sample,the effective overlap width of the multi-layer additive sample is significantly increased,but the load-bearing capacity is slightly weaker.When the rotational speed stay unchanged,the load-bearing capacity of the sample gradually increases with the increase of the traveling speed within a certain range.The compression-shear experiment indicates that the weakest area of the multilayer additive manufacturing sample is the cold lap defect of the first layer.There is a certain hardness change in the hardness among the layers.Multiple thermal inputs lead to the dissolution of the precipitated phase,the hardness gradually decreases from the upper layer to the lower layer.The use of welding tool assembled by stirring pin with features of thread and three milling facets and selfconstrained stationary shoulder can prevent material overflow to a certain extent,and suppress hook defects to a certain extent.Adopting opposite traveling direction of the upper layer and the lower layer can suppress the lower layerfrom growing hook defects to a certain degree.The corrosion resistance of the 2195 aluminum-lithium alloy sample manufactured by FAST is analyzed.Through the polarization curve and electrochemical impedance spectroscopy,explore the corrosion potential and corrosion current of different microregions.It is confirmed that there is a certain corrosion potential difference in each microregion of the structure,which form a corrosion couple in the experiment,and the corrosion potential of the weld nugget region is the highest.During the entire corrosion process,WNZ is obviously protected as a cathode.There is a certain potential difference among each layer of the structure.The corrosion potential of the structure gradually increases from the fifth layer to the first layer,and the corrosion rate gradually slows down from the fifth layer to the first layer.During the process of intergranular corrosion,the corrosion depth of BM area is greater than that of t HAZ and the WNZ.During the FAST process,the precipitated phase particles in the WNZ are solid-dissolved and then precipitated into fine particles,the Cu content in the matrix is increased,so the intergranular corrosion resistance is better.