Modelling recrystallization after hot deformation of aluminium

A physically based model for predicting recrystallization microstructures and textures after hot deformation of aluminium is presented. The modelling approach taken differs from similar models developed for steels. The present model is based on recent experimental investigations directed towards identifying the nature of the nucleation sites for recrystallized grains of different crystallographic orientations. Particle stimulated nucleation, nucleation from cube bands and nucleation from grain boundary regions have been incorporated in the model. The model has been applied to predictions of recrystallized grain sizes and textures of a hot deformed AlMgMn alloy and a commercial purity aluminium alloy. The model responds in a correct way to variations in strain, Zener-Hollomon parameter, initial grain size, initial cube fraction and precipitation. The good agreement between model predictions and experimental results confirms that the recrystallized cube grains are nucleated from “old” cube grains that were present in the starting material and survived the deformation.     

A study on the formation mechanisms of the cube recrystallization texture in cold rolled Fe–36%Ni alloys

The formation of sharp cube recrystallization texture after high cold rolling reductions in Fe–36%Ni has been studied by means of X-ray texture measurements and extensive transmission electron microscopy (TEM) observations, including orientation measurements even in highly deformed materials. In contrast to Cu and Al, this material shows only little recovery during cold deformation; therefore, the deformation structure can be studied in detail. After high cold rolling the cube grains present at the hot rolled state show the formation of cells and the development of a large orientation gradient inside cube bands. During recrystallization nucleation of cube grains proceeds at a high rate inside these structures. For low deformations cube grain nucleation seems to be inhibited due to the insufficient orientation gradient across the cells. Regions of other orientations show a much lower nucleation rate owing to their inappropriate microstructure. Thus, other recrystallization textures only develop if the cube nucleation is inhibited.     

Cube orientation in hot rolled high purity aluminum plate

X-ray diffraction and orientation mapping in EBSD measurement were applied to obtain information of deformation and recrystallization with the emphasis on the cube orientation in hot rolled high purity aluminum plates.It is shown that cube orientations are retained to a large extent during hot rolling.Some deformed cube grains are found to have experienced large extent of recovery according to their Kikuchi band contrasts.The deformed cube-oriented grains in hot rolled plates are in an unfavorite growth condition with respect to their neighboring grain orientations for the subsequent annealing.The reasons for the phenomena observed,as well as the influence of hot rolling process on subsequent cold rolling and final annealing were discussed.     

Cold rolling and recrystallization textures of a Ni–5 at.% W alloy

The formation of recrystallization texture has been studied in a sintered Ni–5 at.% W alloy after heavy cold rolling (～95%) and annealing. Although the cold-rolled texture is a typical pure metal or Cu-type deformation texture on a global scale, variations in microstructure and microtexture are found in the deformed material between locally sheared regions and away those from these regions. The primary recrystallization texture consists of the cube ({1 0 0}〈0 0 1〉), a RD-rotated cube ({0 1 3}〈1 0 0〉) and twin-related orientations of these two components. The presence of both cube and the RD-rotated orientations are identified in thin bands of materials in the deformed matrix. However, predominantly cube-oriented grains nucleate and grow in regions away from the locally sheared regions. In contrast, the nucleation and growth of non-cube grains are observed in the vicinity of locally sheared regions. The formation of cube texture in Ni–5 at.% W alloy appears to occur primarily via the oriented nucleation of cube grains owing to the special properties of the cube bands.     

轧制Al—Mn合金再结晶过程中立方织构的形成

用微观织构分析法天空了轧制Ａｌ－Ｍｎ合金变形组织中的立方带、辩证喧形核及立方晶粒的生长。观察到两种形貌特征的立方带。立方带与其周围基体的取向梯度变化不具有Ｄｉｌｌａｍｏｒｅ－Ｋａｔｏｈ模型关于立方过渡带的特征。立方带中的亚晶及立方带上形成的新晶粒的取向为取向并有绕ＲＤ或ＴＤ的转动;随形变量的加大,绕ＲＤ转动的立方晶粒增多,绕ＴＤ转动晶粒逐渐消失;低温退火时,立方带形核并没有明显的优势;但立方晶粒的     

Moderation of the recrystallization texture by nucleation at copper-type shear bands in Al-1Mg

The critical dependency of copper type shear band formation on deformation variables in Al-1Mg has been described (Acta mater., 49 (2001) 2739). The influence of copper type shear bands on recrystallization behaviour during post-deformation annealing in Al-1Mg is now discussed. Local orientation measurements and orientation images of grains nucleating at shear bands have been made using the electron back-scatter diffraction (EBSD) technique. Bulk recrystallization texture is investigated from X-ray diffraction (XRD) measurements. Shear bands are shown to be potent nucleation sites during annealing and a weak, almost random, texture associated with nucleation at shear bands has been inferred. Most significantly, shear band formation is found to have a pronounced moderating influence on the strength of the potentially dominant cube component of the recrystallization texture.     

铁硅合金轧制-退火过程中立方取向晶粒的形核与长大

利用金相显微镜和EBSD技术分析研究了Fe-3.2%Si合金二次冷轧织构、(100)[001]立方取向晶粒形核、初次再结晶以及二次再结晶后立方织构的形成。结果表明,二次冷轧之后的织构主要为{111}<112>和{111}<011>,并存在少量的{112}<110>,同时在变形晶粒内部存在有接近{100}<001>取向的微区。冷变形晶粒内部各微区取向连续变化,并且逐渐向近立方取向靠近。冷变形晶粒内部立方取向的微区作为形核的核心,在退火过程中利用(100)晶粒低表面能和γ→α相变最终发展成为具有集中立方织构的柱状晶组织。     

W含量对Ni-W合金基带取向及织构形成的影响

采用压延辅助双轴织构基板制备路线,结合X射线衍射和电子背散射衍射技术,系统研究了W量(原子分数)分别为5%、7%和9.3%的Ni-W合金基带在冷轧形变和再结晶热处理过程中的取向及织构形成的变化规律。研究发现,在冷轧形变过程中,随着W含量的增加,Ni-W合金基带中S和Copper取向含量的增量逐渐降低,而Brass取向含量的增量则呈现上升趋势,最终低W合金获得Copper型轧制织构,而高W合金获得Brass型轧制织构。在再结晶热处理过程中,低W合金立方晶粒形核较早并迅速长大,吞并其它取向,容易获得立方织构;高W合金的立方取向晶粒则和其它取向晶粒一同形核和长大,且长大速度不及其它取向晶粒,最后形成杂乱取向。     

Recrystallization behavior of high purity aluminum at 300 °C

The recrystaliization behavior of 98.5% cold rolled high purity aluminum foils annealed at 300 °C was investigated, and the evolution of the microstructures was followed by electron back scattered diffraction(EBSD). The results show that the recrystaliization process of the high purity aluminum foils at 300 °C is a mixture of discontinuous- and continuous-recrystallization. The orientations of the recrystaliization nuclei include not only the cube orientation, but also other orientations such as some near deformation texture components which are the results of strong recovery process. However, such continuously recrystallized grains are usually associated with relatively high free energy, so they would be consumed by the discontinuously-recrystallized grains (cube-oriented grains) in subsequent annealing. On the other hand, the pattern quality index of recrystallized grains shows dependence on the crystal orientation which might introduce some errors into evaluating volume fraction of recrystaliization by integrating pattern quality index of EBSD.     

Investigation on the Recrystallization Mechanism in Warm-Rolled Ti-IF Steel

The nuclei orientation, the nucleation site at the early stage of recrystallization, and the growth mechanism of the nuclei have been studied by EBSD analysis in Ti-IF steel during direct annealing after warm rolling. It is concluded that the formation of the recrystallization texture is dominated by the oriented nucleation mechanism. The recrystallized nuclei with γ-orientation emerged preferentially at the beginning of recrystallization and preferred to form in the deformed bands with γ-orientation and on the boundaries between γ- and α-orientations. The recrystallized grains first consumed their neighboring γ-oriented matrix; and then consumed the α-oriented deformed bands at the late stage of recrystallization, leading to strong γ-fiber.     

PARTICLE STIMULATED NUCLEATION AND THE FORMATION OF RSCRYSTALLIZATION TEXTURE IN Al-Mn ALLOY CONTAINING PARTICLES Ⅱ. Interaction Between Particles and Other Nucleation Sites and the Formation of Recrystallization Texture

本文报了Ａｌ－Ｍｎ合金形昧形变取向基体中粒子周围亚晶转动规律及对应的粒子促进形核晶粒的取向特征的基础上,进一步测定了处在晶界,立方带上的了周转新晶粒的取向分布。     

Al—Mn合金中粒子促进形核及初期再结晶织构 Ⅱ.粒子与其它形核位置的交互作用及初期再结晶织构

本文在分析了Al—Mn合金形变时不同形变取向基体中粒子周围亚晶转动规律及对应的粒子促进形核晶粒的取向特征的基础上,进一步测定了处在晶界,立方带上的粒子周围新晶粒的取向分布,最后分析了再结晶织构的形成．结果表明,处在这些位置上的粒子周围新晶粒一方面保留了晶内PSN晶粒的取向特征,另一方面也带有晶界及立方带形核的特点再结晶织构反映了不同类型形核位置形成的新晶粒的取向特征     

Formation of recrystallization cube texture in high purity face-centered cubic metal sheets

An investigation on recrystallization textures in high purity face-centered cubic (fcc) aluminum, copper, and nickel indicated that the cube texture is a unique dominant final texture. In a macroview of rolling deformation, a balanced activation of four slip systems can result in certain stability of some substructure with cube orientation in the deformed matrix. In the stable substructure the dislocation density is very low, and the dislocation configuration is rather simple in comparison to other orientations so that the cube substructure can easily be transformed into cube recrystallization nuclei by a recovery process. A high orientation gradient and correspondingly high angle boundaries to the deformed matrix are usually expected around the cube nuclei, which, therefore, grow rapidly. After the primary recrystallization, the size of cube grains is much larger than the grains with other orientations, which will be expensed as the cube grains grow further, so that the cube texture can finally become a dominant texture component.     

Zr-Sn-Nb新型锆合金板材加工过程中不均匀组织与织构演变

利用XRD,SEM-ECC,TEM和EBSD技术,研究了Zr-Sn-Nb系新型锆合金板材加工过程的微观组织及织构演变.结果表明,β相淬火得到的随机织构经热轧后形成沿横向倾斜的基面织构,随后的加工过程均保留该织构;热轧及两次冷轧后的基面织构都为〈1010〉方向平行于轧向(〈1010〉//RD),而退火后转变为〈1210〉方向平行于轧向(〈1210〉//RD).淬火形成的网状魏氏组织经热轧转变为不均匀形变组织,两次冷轧使组织的不均匀性更显著,最终退火得到完全再结晶组织;轧制形成的难变形晶粒多为晶粒C轴平行于轧板法向(C//ND)的取向;最终退火板材的大晶粒多为〈1210〉//RD的基面织构,小晶粒则以〈1010〉//RD为主.结合锆合金的变形及再结晶机制对轧制时产生的不均匀组织及再结晶过程的织构转变进行了分析.     

冷轧TA5钛合金退火过程的再结晶行为及织构演变

采用电子背散射衍射技术(EBSD)对冷轧及退火态TA5钛合金板材的晶粒尺寸、再结晶及织构进行了表征,并讨论了变形不均匀对再结晶行为及织构演变的影响。结果表明:<0002>//TD取向晶粒比<0002>//ND取向晶粒更容易发生变形,结合hcp结构滑移系统的有限性,共同决定了TA5合金板材冷轧变形具有不均匀性的特点。退火早期再结晶在局部应变大的区域快速形核,且变形量越大,形核数量也越多,再结晶后样品的晶粒尺寸也越小。局部应变大的区域在退火早期以“定向形核”机制快速发生再结晶形核并长大,包括少量剩余的严重变形<0002>//TD取向晶粒;同时,其余应变较低的组织在再结晶形核全过程以“应变诱发晶界迁动形核”机制缓慢形核,这两种机制共同作用导致退火后板材的织构弱化,但仍以冷轧态的基面织构为主。硬度变化曲线可以很好的反映再结晶程度;但受织构影响,不同测试面的硬度值存在显著差异,加载轴与晶体c轴之间的夹角越大,硬度值越小。     

Texture after ECAP of a cube-oriented Ni single crystal

The texture of a cube-oriented Ni single crystal after one-pass equal channel angular pressing (ECAP) was measured globally and locally by neutron and synchrotron radiation, respectively. The texture is characterized by a TD rotated cube, a split C component and a partial B fiber. These components are heterogeneously distributed in the ECAP billet. Due to friction at the die walls, the rotated cube is mainly observed in the top and bottom parts of the billet, the split C dominates in the central part. The experimental results with respect to component intensity, position from ideal orientation and asymmetry of component splitting are compared with texture simulations taking into account grain fragmentation. Conclusions concerning polycrystal deformation are drawn.     

Zr-sn-Nb新型锆合金板材加工过程中不均匀组织与织构演变

利用XRD,SEM-ECC,TEM和EBSD技术,研究了Zr-Sn-Nb系新型锆合金板材加工过程的微观组织及织构演变.结果表明,β相淬火得到的随机织构经热轧后形成沿横向倾斜的基面织构,随后的加工过程均保留该织构;热轧及两次冷轧后的基面织构都为(1010)方向平行于轧向((1010)∥RD),而退火后转变为(1210)方向平行于轧向((1210)∥RD).淬火形成的网状魏氏组织经热轧转变为不均匀形变组织,两次冷轧使组织的不均匀性更显著,最终退火得到完全再结晶组织;轧制形成的难变形晶粒多为晶粒C轴平行于轧板法向(C∥ND)的取向;最终退火板材的大晶粒多为(1210)∥RD的基面织构,小晶粒则以(1010)∥RD为主.结合锆合金的变形及再结晶机制对轧制时产生的不均匀组织及再结晶过程的织构转变进行了分析.     

Influence of initial textures on dynamic recrystallization and textures in AZ31 magnesium alloys

1　INTRODUCTIONMagnesiumisthelightestmetallicstructurema terialwithhighspecificstrengthandthereforeiswidelyusedinautomotive ,electronicsandaerospaceindustries[1,2 ] .However ,magnesiumoftenshowsinsufficientplasticityatroomtemperatureduetoitsHCPstructurewithlessindependentsystemsofbasalslip .Toenhanceformabilityofmagnesium ,ahigherdeformingtemperatureisusuallyusedwithtwopur poses .Thefirstistoactivatenewslipsystemsbesidesbasalslip ,sothatmorethanfiveindependentslipsystemscanbeprovided ,be…     

PARTICLE STIMULATED NUCLEATION AND THE FORMATION OF RECRYSTALLIZATION TEXTURE IN Al-Mn ALLOY CONTAINING PARTICLES Ⅰ. Deformation Zones Around Particles and Particle Stimulated Nucleation

利用ＳＥＭ中的和射电子衍射技术研究了Ａｌ－１．３Ｍｎ（质量分数,％）合金中没形变取向基体中粒子周围亚晶以及再结晶初期相应的粒子促进形核晶粒的取向分布,并将结果与单昌中的情形进行了比较。