Effect Of Thickness Rolling Pass Reduction On Microstructure And Properties Of Asymmetric Rolling 6016 Aluminum Alloy Sheet

Strong shear asynchronous rolling of 6016 aluminium alloy sheet for automobile body was carried out by thickness reduction per pass(TRPP)process.The microstructural characteristics of 16%,27%,40% and 60% pass reduction rates after asynchronous rolling and solution treatment were analyzed by optical microscopy(OM),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The macroscopic texture information of 6016 aluminium alloy rolled and solid solution sheets was collected by X-ray diffraction(XRD).The evolution of sheet texture during asynchronous rolling and the influence of different TRPP on the deformation texture,shear texture and recrystallization texture of rolled and solid solution sheets were analyzed.The mechanical properties and forming properties of the sheet before and after solution treatment in the rolling direction of 0,45 and 90 directions were measured and analyzed by universal tensile test machine and cupping test machine,and the corresponding anisotropy index and plastic strain ratio was calculated.Combining with the process of strong shear deformation and recrystallization mechanism,the changes of structure and properties of sheets with different TRPP were discussed,and the relationship between texture and properties of aluminium alloy sheets was explored.The main results are as follows:1、 The grain morphology and second phase particle morphology of 6016 aluminum alloy sheet with different TRPP were analyzed.The grains of the initial hot rolled slab distribute in strip shape along the rolling direction,and the grains are coarse and uniform.The grain of rolled sheet is compressed and elongated in strip shape.With the increase of deformation,the grains mainly distribute in flakes.When the final thic kness is reached,the grains show a slender strip,and the second rod-like phase is distributed in a discontinuous chain along the rolling direction.With the increase of pass reduction rate,the deformation characteristics are obvious,the grain spacing narrows,the number of second phases increases,and they are evenly distributed in the matrix.After solution,the grains in the matrix exist in the form of equiaxed grains.The average grain sizes of 16%,27%,40% and 60% solid solution sheets are 69.6m,7 8.1m,77 m and 44.5m,respectively.The content of the second phase particles in the matrix is relatively small,but there are still a few insoluble coarse second phases.With the increase of pass reduction rate,the second phase particles break up and disperse in the matrix,which is conducive to the recrystallization of the sheet.2 、 The texture changes of 6016 aluminium alloy as-rolled sheet rolled by asynchronous rolling with different TRPP were investigated.The texture configurations of rolled sheets with different TRPP are similar to those of original sheets.The main deformation textures are Brass texture,Copper texture and S texture.E,F shear texture,and Cube recrystallizatied texture.With the increase of rolling deformation,the deformation texture strength increases,the shear texture strength increases,and the recrystallization texture does not change significantly.When rolling to the final thickness,the texture strength of the rolled sheet varies with the reduction rate.With the increase o f reduction rate,the deformation texture strength of the rolled sheet decreases,and the shear texture and rotating cubic texture strength increase significantly.3、 The texture changes of 6016 aluminum alloy soluted sheet during asynchronous rolling with different TRPP were investigated.After solution treatment,the deformation texture and shear texture strength of the sheet decreased,while the rest texture tended to random orientation distribution.The recrystallization texture strength of the solid solution sheet increased,showing Cube cubic texture as the main component,Goss,P,Q and R texture coexisting.This is due to the cubic band nucleation and particle-promoted recrystallization nucleation during solution,which makes the recrystallization text ure of the sheet diversified.The shear texture strength of soluted sheets with different TRPP is not significantly different.With the increase of TRPP,the texture distribution of soluted sheets becomes more diffuse and the overall texture strength weake ns.4、 The mechanical properties and forming properties of sheets with different reduction rates before and after solution were stuied,and the corresponding anisotropic index and plastic strain ratio was calculated.Compared with the original sheet,the tensile strength and yield strength of the sheet increased,while the elongation decreased after asynchronous rolling.With the increase of pass reduction rate,the average tensile strength increases while the elongation decreases.After solution treatment,the sheets were strengthened by solution treatment,and the tensile strength and elongation increased to about 30%.Increasing the TRPP is helpful to increase the r value of the sheet,while reducing theΔr value.The thickness anisotropyΔr value is lower than 0.2,and the IE value of the sheet increases,and increases with the TRPP.5、 The relationship between microstructures and anisotropy of rolled sheets with different pass reduction rates was analyzed.The Planar Anisotropy of as-rolled sheet with the same pass reduction rate is obvious.The measured strength of as-rolled sheet in 0(RD),45(AD)and 90(TD)directions is RD>AD>TD.The strip grain morphology along the rolling direction makes the grain boundary ha ve the greatest effect on the rolling strengthening,while the rod-like second phase along the rolling direction has the greatest effect on the TD direction of the sheet.The interaction of grain boundary,second phase and texture leads to the anisotropy o f mechanical properties of rolled sheets.After solution treatment,the Planar Anisotropy of sheet metal decreases significantly.IPA indices of four solid solution sheets with different pass reduction rates are 2.21,4.52,2.44 and 2.92,respectively.Solution treatment is beneficial to improving the formability of sheet metal.6、 The mechanism of effect of asynchronous high shear rolling with TRPP on shear texture and formability of 6016 aluminum alloy sheet was discussed.From the calculation of the ideal texture components,it can be seen that the strong shear texture of E and F can not only increase the plastic strain ratio r,but also reduce theΔr value.When rolling TRPP is increased,the external shear stress acting on the rolled sheet can be effectively increased,and the effect of strong shear deformation will be greater.It will promote the formation of more E and F strong shear texture,which is beneficial to increase the plastic strain ratio r value and reduce the thickness anisotropyΔr value of the sheet.When the TRPP is 60%,the shear texture strength of as-rolled and soluted sheets is relatively high,with high r value and IE value,and lowΔr value.