Effects Of Processing Parameters On Mechanical Property And Microstructure Of 2195-T8 Al-Li Alloy During Friction Stir Welding

In the present work,2195-T8 Al-Li alloys with 7.5mm in thickness were used as base material to fabricate fricition stir welding?FSW?butt joints under various welding parameters.Tensile test,scanning electron microscopy?SEM?and electron backscattered diffraction techniques?EBSD?were employed to characterize mechanical propersites and microstructure evolution of joints.The relationship between grain size,precipation,texture component and meachanical properties of joints were analyzed.The friction stir welding window of 2195-T8 Al-Li alloys were constructed.The results can be summarized as follows:?1?Tensile strength would decrease with the increasing of advancing speed,while kissing-bond defect occurred in the root of joints.Tensile strength would decrease with the increasing of rotation speed,while so called tunnel defect occurred in nugget zone?NZ?.?2?Hardness profile of joints on cross section shows a W shape and the hardness in NZ decreases from top to bottom along vertical direction.Grain size decreases from top to bottom in NZ,while grain size decreases with the increasing of advancing speed.Precipitation in joints puts greater effect on mechanical properties than grain size.?3?Proper welding parameters range of this alloys was narrow,in which the advancing speed was limited from 50 mm*min^-11 to 70 mm*min^-11 and the rotation speed was limited from 500 r*min^-1 to 700 r*min^-1.Defect-free joints can obtain due to sufficient heat input in this range.Defect-free joints would fracture along 45°within TMAZ during tensile test.When heat input were too high or too low,sorts of defects would occurr in NZ of joints which would deteriorate mechanical properties of joints.?4?Similar high angle boundaries?HABs?content?about 70%?and grain size?about 5?m?in middle NZ show similar thermal cycle within middle NZ of joints under various advancing speed.HABs content and grain size increase with the increasing of rotation speed,while grain size remains around 5?m under 1000 r*min^-1-50 mm*min^-1welding parameter due to uneven heat input distribution.Recrystallization occurred in joints due to severe plastic deformation.Main recrystallization mechanisms are continuous dynamic recrystallization?CDRX?and geometry dynamic recrystallization?GDRX?.?5?Complicated evolution of texture components occurred in the boundary area between TMAZ and NZ.Severe plastic deformation would result in the rotation of original grains,which would turn rolling texture components into new deformation texture components like S texture component.With approaching to NZ,recrystallization texture components,like Cube component and Goss texture component,occurred due to increasing deformation and temperature.