Study On Texture Evolution And Formation Mechanism Of HCP-structured Materials With Double-peaked And TD-tilted Texture

Magnesium and titanium with a HCP structure are important materials for lightweight structures and have important applications in aerospace,national defense and military industries.Rolling sheets of the above two kinds of materials all have basal plane bimodal texture with transverse deflection(TD)along the sheet,which has a significant effect on the plastic deformation and forming.However,the evolution and formation mechanism of the texture under different stress states have not been systematically studied.In this paper,the influence of different stress states and annealing treatment on the texture evolution of Mg-2Zn-2Gd、Mg-2Zn-1Gd and pure Ti plate was studied by combining the microstructure characterization and crystal plasticity simulation,and the formation mechanism of texture under different stress states was mainly revealed.Specifically,Chapter 2 studies the texture evolution of a cross-rolled Mg-2Zn-2Gd plate after unidirectional rolling.In chapter 3,the formation mechanism of a TD-deflection texture Mg-2Zn-1Gd rare earth magnesium alloy in rolling process was studied.In chapter 4,the evolution and mechanism of texture of industrial pure titanium under different strain paths and strain variables are studied.In chapter 5,the influence of crystal plasticity simulation parameters on the mechanical behavior of pure titanium is studied.The main conclusions are as follows:1 After unidirectional rolling and annealing of Mg-2Zn-2Gd cross-rolled plate,the circular texture can be partially retained in the cross-rolled plate,and the grain C axis is distributed on the ellipse about 30°-40° from the normal direction.The texture changes before and after one-way rolling and annealing were compared quantitatively.The annular texture before unidirectional rolling and annealing is partly inherited from that before unidirectional rolling.There is no obvious relationship between the orientation of recrystallized grains and that of deformed grains in the annealing process after unidirectional rolling.The mechanical anisotropy of the two specimens is very different,that is,the anisotropy of the yield strength is low when the cross rolled plates are stretched along the Rd and Td directions,but the yield asymmetry appears on the unidirectional rolled plates.Under the unidirectional rolling condition,the sliding rate of cylinder activated by stretching along RD is much higher than that of stretching along TD,and the CRSS of cylinder sliding is significantly higher than that of base plane sliding,resulting in the yield strength of stretching along RD is significantly higher than that of stretching along TD.2 Tensile,compression and rolling tests were used to analyze the texture evolution of Mg-2Zn-1Gd.The results show that both the rolling deformation texture and the annealing texture is similar to the texture of unaixal tension.This indicates that the texture evolution mechanism of rolling deformation is similar to that of tensile deformation,but obviously different from that of compression deformation.The deformation mechanism of tensile strain along rolling direction plays an important role in the formation of texture.After annealing,the two peaks of the base plane are distributed in a direction perpendicular to the direction of tensile strain.The main deformation modes under tensile deformation are basal slip and prismatic slip.The main deformation mode under compression deformation is basal slip.There is more prismatic slip along RD tensile deformation and rolling than along TD,is the cause of the difference between the texture along RD and TD direction.3 For pure Ti,tensile deformation should be even larger variable can also be difficult to make significant changes in texture,relatively speaking,in the process of compression deformation texture change is more significant,after compression deformation will form two texture components,namely the initial texture components and compression deformation texture components,grain c axis compression deformation texture component nearly parallel to the direction of compression.Under different strain paths,the deformation mode(the ratio of cylinder slip)at the beginning of deformation is different to some extent.The ratio of edge slip activated by stretching along the RD direction is much higher than that of stretching along the TD direction.The CRSS of cylinder slip is obviously lower than that of base plane and cone slip,and the yield strength of RD is lower than that of TD,This is different from Mg-Zn-Gd plates.The starting rate of cylinder slip during compression is RD>TD>ND,and the yield strength is ND>TD>RD.Under different strain,the dominant deformation mode changes significantly with the increase of deformation degree.Basal slip or pyramidal slip or {1012} tensile twin grain number is more,leading to the formation of the main causes of different texture.4 The Tangent SCS allows a slightly better reproducibility of the available stress-strain curves.The {1122} twin volume fraction depends on the SCS but not the{1012} twin volume fraction.The Tangent SCS seems to better reproduce the r-values,because it predicts a more isotropic behavior.On the opposite,the Affine SCS over-estimate the plastic anisotropy.To reproduce all the stress strain curves,it is necessary to consider that tension twins harden less prismatic slip in tension than in compression.