Β-fiber Texture Research Articles

Effects of Mn and Zr Addition in 6000 Series Aluminum Alloys on the Formation of Stabilized Substructures during Hot Deformation

Thermal stability of substructures in 6000 series aluminum alloys containing Mn and Zr elements was investigated using plane-strain compression test. In order to form thermally stabilized substructures, the deformation parameters should be selected so as to correlate with kinetic precipitation during the deformation. For substructures of the alloys containing Mn and Zr elements, the substructures were stable during the heat treatment at 540 ̊C when the alloys were deformed at a temperature above 350 ̊C. The sheets rolled above 350 ̊C at a strain rate of under 3 s-1 per pass showed the fibrous structure and well developed β-fiber textures after the heat treatment at 540 ̊C. The sheets with the fibrous structure had an average Lankford value larger than one.

Fabrication of Mg/AL multilayer plates using an accumulative extrusion bonding process

In the present study, Mg/Al multilayer plates with excellent layer-layer bonding were successfully fabricated by co-extrusion of Mg/Al bimetal billets from the as-cast condition. The previously extruded plates were stacked and extruded again, realizing an accumulative extrusion bonding (AEB). Grain structure, transition layer and textures from the surface to the center of composite plates were studied. Our results show that a weakened basal texture with a double peaked basal poles tilting toward the ED and a preferred distribution of prismatic planes exist in the inner Mg layer, in comparison to a much stronger peak of basal poles and a random distribution of prismatic planes in the surface Mg layer. All the Al layers have a strong β-fiber texture and an texture gradient from the surface to the center exists. Both the Mg layer and the Al layer have an inhomogeneous grain structure after the first pass of extrusion. The inner Mg layer has a similar grain morphology to that of the surface Mg layer. Compared to the inner Al layers, the surface Al layer contains more recrystallized grains. A new cycle of AEB at 400°C does not refine grains, but generates more homogeneous grains, which leads to an improved tension elongation.

Mechanical properties of 7475 aluminum alloy sheets with fine subgrain structure by warm rolling

The effect of transition elements on grain refinement of 7475 aluminum alloy sheets produced by warm rolling was investigated. The alloy which contains zirconium instead of chromium showed ultra fine structures with stable subgrains after warm rolling at 350 °C, followed by solution heat treatment at 480 °C. The average subgrain diameter was approximately 3 μm. It became clear that zirconium in solution has the effect of stabilizing subgrains due to precipitation of fine Al3Zr compounds during warm rolling. On the other hand, chromium-bearing compounds precipitate before warm rolling and they grow up to relatively large size during warm rolling. The warm rolled sheets with fine subgrains have unique properties compared with conventional 7475 aluminum alloy sheets produced by cold rolling. The warm rolled sheets solution heat treated had subgrain structures through the thickness with a high proportion of low-angle boundary less than 15°. The strength of the warm rolled sheets in T6 condition was about 10% higher than that of conventional 7475 aluminum alloy sheets. As the most remarkable point in the warm rolled sheets, the high Lankford (r) value of 3.5 was measured in the orientation of 45° to rolling direction, with the average r-value of 2.2. The high r-value would be derived from well developed β-fiber textures, especially with the strong {011}«211» brass component. The warm rolled sheets also had high resistance to SCC. From Kikuchi lines analysis and TEM images, it was found that PFZs were hardly formed along the low-angle boundaries of the warm rolled sheets in T6 condition. This would be a factor to lead to the improvement of resistance to SCC because of reducing the difference in electrochemical property between the grain boundary area and the grain interior.

{111}<110> Recrystallization Texture Evolution in Al-Mg-Si Alloy Sheets Fabricated by Symmetric/Asymmetric Combined Rolling Process

A new rolling process, which combined asymmetric rolling with symmetric rolling, was adopted in age-hardenable 6xxx series Al-Mg-Si alloy promising as automotive body panels in order to develop favorable textures for the deep drawability after solution treatment. Symmetric cold rolling at high reduction and subsequent asymmetric warm rolling at low reduction for AA6022 sheets led to the formation of “TD-rotated β-fiber texture” including moderate {111}<uvw>-oriented components, resulting in noticeable evolution of {111}<110> recrystallization texture during the solution treatment at a high temperature. The results of texture analysis and microstructural observation suggested that the low stored energy after asymmetric warm rolling, the high fraction of high angle boundaries with neighboring deformed matrices and the approximate 40° <111> orientation relationship with deformed matrices would strongly affect the evolution of {111}<110> recrystallization texture.

Texture and mechanical properties of Al-0.5Mg-1.0Si-0.5Cu alloy sheets manufactured via a cross rolling method

The relationship between the texture and mechanical properties of 6xxx aluminum alloy sheets processed via cross rolling was investigated. The microstructures of the conventional rolled and cross rolled sheets after annealing were analyzed using optical micrographs (OM). The texture distribution across the thickness in the Al-Mg-Si-Cu alloy, conventional rolled sheets, and cross rolled sheets both before and after annealing was investigated via X-ray texture measurements. The texture was analyzed in three layers from the surface to the center of the sheet. The β-fiber texture of the conventional rolled sheet was typical of the texture obtained using aluminumoll ring. After annealing, the typical β-fiber orientations were changed to recrystallization textures: cube{001}〈100〉 and normal direction (ND)-rotated cubes. However, the texture of the cross rolled sheet was composed of an asymmetrical, rolling direction (RD)-rotated cubes. After annealing, the asymmetrical orientations in the cross rolled sheet were changed to a randomized texture. The average R-value of the annealed cross rolled sheets was higher than that of the conventional rolled sheets. The limit dome height (LDH) test results demonstrated that cross rolling is effective in improving the formability of the Al-Mg-Si-Cu alloy sheets.

Texture Control of Aluminum and Magnesium Alloys by the Symmetric/Asymmetric Combination Rolling Process

In order to develop favorable textures for deep drawing of Al-Mg-Si and Mg-Al-Zn alloys that are promising as automotive body panels, we have adopted the symmetric/asymmetric combination rolling (SACR) process consisting of conventional symmetric rolling and subsequent asymmetric rolling at relatively low reduction. The combination of symmetric cold rolling and asymmetric warm rolling for AA6022 sheets leads to the formation of “TD-rotated β-fiber texture”, resulting in the evolution of {111} recrystallization texture after solution treatment at a high temperature. The SACR processed and solution-treated sheets show a high average r-value with small in-plane anisotropy, and consequently the limiting drawing ratio increases significantly, compared to that of the cold-rolled and solution-treated sheets. In the case of AZ31 magnesium alloy, the SACR process by hot rolling causes the formation of a unique texture, which shows two (0001) poles with tilt angles of 0 and −40 degrees from the normal direction (ND) toward the rolling direction (RD). In addition, subsequent annealing weakens intensity of the double-peak texture, so that the drawability is greatly improved in comparison with that of the conventional warm-rolled sheets with a strong basal texture. At the same time, yield strength decreases to some extent, but the SACR processed and annealed sheets exhibit a good balance of strength and formability due to a mixed texture with basal and tilt components.

Texture Distribution through Thickness in 6xxx Aluminum Alloy Sheet Fabricated by Cross-Roll Rolling Method

Texture distribution through thickness in 6xxx aluminum alloy cross-roll rolled sheet has been investigated using the electron back-scattered diffraction (EBSD) technique. Analyses of texture in three layers from the surface to the center of the sheet were performed. Near the surface, shear type textures including {012}<142> orientation and {112}<110> orientation were found and β-fiber texture were dominating. In the center layer, very weak β-fiber texture {112}<111> orientation, {123}<634> and {011}<211> were found with Cube, Cube-ND and Goss orientation plus others.

Influence of the Processing Temperature on the Microstructure, Texture, and Hardness of the 7075 Aluminum Alloy Fabricated by Accumulative Roll Bonding

The 7075 alloy is an Al-Zn-Mg-Cu wrought age-hardenable aluminum alloy widely used in the aeronautical industry. The alloy was accumulative roll bonded at 300 °C (573 K), 350 °C (623 K), and 400 °C (673 K), and the microstructure, texture, and hardness were investigated. Cell/(sub)grain size in the nanostructured range, typical β-fiber rolling texture, and homogeneous hardness through thickness were determined in all cases. Misorientation was different at each processing temperature. At 400 °C, the presence of elements in solid solution and the partial dissolution of the hardening precipitates lead to a poorly misoriented microstructure with a high dislocation density and a homogeneous β-fiber texture of low intensity, typical of intermediate degrees of rolling. At 350 °C and 300 °C, highly misoriented microstructures with smaller dislocation density and intense heterogeneous β-fiber rolling texture are observed, especially at 350 °C, wherein the degree of dynamic recovery (DRV) is higher. Hardness of the accumulative roll bonded samples is smaller than that of the starting material due to particle coarsening, and it is affected by solid solution and/or by fine precipitates produced by reprecipitation of the elements in solid solution.

Evolution of Rolling Textures of Cold Rolled Copper Foils

The texture evolution of cold rolled tough pitch copper foils could be changed by altering the initial texture and microstructure before cold rolling. The development of β-fiber texture was substantially suppressed even after 92% reduction for the case of abnormally coarse initial grain structure and extremely strong initial cube texture. Instead, the intensity of cube and RD (rolling direction)-rotated cube texture components was increased continuously by increasing the intensity of the initial cube texture.

Anomalous Rolling and Annealing Textures of Cold Rolled Copper Foils

Copper foils cold rolled up to 92% reduction exhibited a low intensity of the β-fiber texture and a high intensity of the cube and RD (rolling direction)-rotated cube components. After annealing, the recrystallization texture of the foils could be characterized by the mixture of the cube and the S components. An initial strong cube texture with a large grain size might remain a less developed rolling texture component, cube or RD-rotated cube, which would be the source of the S component in the recrystallization texture.

Recrystallization Textures of Al-Mg-Si Alloy Sheets Produced by Symmetric and Asymmetric Combination Rolling

In order to improve deep drawability of 6000 series aluminum alloys for automotive body panels, texture control for increasing r-value of the sheets was attempted by combination of symmetric and asymmetric rolling. Asymmetric warm rolling at relatively low reduction after symmetric rolling made it possible to form TD-rotated β-fiber texture including {111} components. Recrystallization textures of the T4-treated materials varied significantly depending on roll speed ratio and reduction in asymmetric warm rolling. On appropriate rolling conditions, {111}<110> orientation with high r-value was formed as a main component of recrystallization texture. On the other hand, two-stage heat treatment consisting of low temperature annealing and subsequent T4-treatment led to a significant change in recrystallization texture. In the sample annealed for long time at a low temperature, TD-rotated β-fiber rolling texture was retained even after solution treatment at a much higher temperature, because recovery or recrystallization took place to some extent during low temperature annealing.

Texture evolution rate in continuous cast AA5052 aluminum alloy during single pass hot rolling

Continuous cast AA5052 Al alloy slab was hot rolled by a single pass with entrance and exit temperatures of 482 °C and 400 °C, respectively. The thickness of the slab was reduced from 21.5 mm to 8.6 mm. The evolution of texture and microstructure during the rolling was investigated by X-ray diffraction, SEM and optical microscopy. It was found that the grain structure changed from equiaxed to elongated in shape in the alloy at a rolling reduction over 38%. With increase in rolling reduction, the β-fiber texture was increased rapidly in the expense of the remainder component, while the rest of the texture components were only changed slightly during the hot rolling. The evolution of different texture components during the hot rolling process was quantified using modified Johnson–Mehl–Avrami–Kolmogorov-type equations. The corresponding evolution rates were also computed from these equations. Among the three main components (copper, brass and S) in β-fiber, the copper component was the strongest, having the fastest evolution rate, and S the weakest, during hot rolling.

Development of textured Ni substrates prepared by powder metallurgy and casting

We fabricated the textured Ni substrate for YBCO coated conductors and evaluated the effects of processing variables on microstructural evolution and texture transformation. Initial specimens were prepared by two different methods, i.e., powder metallurgy (P/M) and casting. To characterize the role of two preparation methods, the initial specimens of the same size were prepared under the same rolling and annealing conditions. The microstructure and texture were evaluated by orientation distribution function (ODF), electron backscattering diffraction and transmission electron microscopy with selected area diffraction. We observed that the microstructure of the rolled tape varied with preparation methods; the rolled tape prepared by P/M had more deformation bands and stronger β-fiber texture than that one obtained by casting, resulting in finer microstructure and stronger cube texture after recrystallization. The smaller grains in the former tape were explained by the “variation inhibition theory” together with in situ TEM result. Texture analysis indicated that the substrate made by P/M had a stronger cube texture and a wider annealing temperature range in which the cube texture became stable, compared to that of the casting-substrate. In addition, abnormal grain growth occurred and consequently formed high angle grain boundary for substrate by casting but not for substrate by P/M.

Improvement of Mechanical Properties of 7475 Based Aluminum Alloy Sheets by Controlled Warm Rolling

An attempt was made to refine the grain structure of 200 mm wide sheets of AA7475 based aluminum alloys containing zirconium by employing a new warm rolling method under the control of both roll temperature and material temperature. The warm rolled sheets as solution heat treated had subgrain structures through the thickness with a high proportion of low angle boundary less than 15°. The average subgrain diameter was approximately 3 μm. The strength of the warm rolled sheets in T6 condition was about 10% higher than that of conventional AA7475 alloy sheets produced by cold rolling. As the most remarkable point in the warm rolled sheets, the high Lankford (r) value of 3.5 was measured in the orientation of 45° to rolling direction, with the average r-value of 2.2. The high r-value would be derived from well developed β-fiber textures, especially with the strong {011} ‹211› Brass component. The warm rolled sheets also had high resistance to SCC. From Kikuchi lines analysis and TEM images, it was found that PFZs were hardly formed along the low angle boundaries of the warm rolled sheets in T6 condition. This would be a factor to lead to the improvement of resistance to SCC because of reducing the difference in electrochemical property between the grain boundary area and the grain interior.

Cold rolling and recrystallization textures in L12-type Co3Ti ordered alloys

The texture development during cold rolling and recrystallization of L12-type Co3Ti alloys was investigated as functions of alloy composition and rolling reduction. Two kinds of fully annealed Co3Ti alloys with different alloy compositions (Co77Ti23 and Co78Ti22), whose initial textures and grain sizes were almost identical, were used. After 70% reduction, the cold-rolling textures of both alloys were composed of strong α-fiber and weak β-fiber textures, in which the intensity of {011}〈211〉 orientation was higher than those of {112}〈111〉 and {123}〈634〉 orientations, indicating that texture transition from copper type to brass type occurred in cold-rolled Co3Ti alloys. This texture transition was more prominently recognized in the Co78Ti22 alloy, whose chemical composition was more off-stoichiometric. On the other hand, the recrystallization textures of both alloys were considerably weak, and their orientation spreads were more significant with increasing rolling reduction. Also, the recrystallization textures were basically independent of alloy composition in contrast to the rolling textures.

Texture evolution during cold rolling and recrystallization of L1 2-type ordered Ni 3(Si,Ti) alloy

Texture evolution during cold rolling and recrystallization of L1 2-type ordered Ni 3(Si,Ti) (Ni 79Si 11Ti 10, denoted by at.%) alloy was investigated. The starting material with no preferential orientation was cold rolled up to 80% reduction, and then fully recrystallized by annealing at 1173 K for 1 h. After cold rolling, a copper type texture composed of the α- and β-fiber textures with the strongest component of {011}〈211〉 orientation was developed. The recrystallization textures depended on rolling reduction. For the 30% reduction, no textural change was observed, while above 50% reduction the recrystallization textures were quite weak, but {011}〈100〉 and {001}〈110〉 orientations apparently existed. Based on these results, formation mechanism for cold rolling and recrystallization textures of the Ni 3(Si,Ti) alloy was discussed and compared with those of other L1 2-type ordered alloys.

The effect of precipitation on the evolution of recrystallization texture in AA8011 aluminum alloy sheet

An AA8011 aluminum alloy sheet cold rolled by 95% had a typical β-fiber texture, which runs from the copper orientation {112}〈111〉 over the S-orientation {123}〈634〉 to the brass orientation {110}〈112〉 in the Euler space. The development of annealing textures depended on annealing temperatures due to the interaction between precipitation and recrystallization. Upon annealing at a low temperature of 275 °C, substantial precipitation took place before recrystallization. This led to a weak recrystallization texture consisting of the P-orientation {011}〈122〉, the cube orientation {001}〈100〉, and the RD rotated cube orientation {hk0}〈001〉, among which the P-orientation, which developed near large FeAl 3 particles, was the main component and the cube orientation originated from the matrix was relatively weak. After annealing at 350 and 500 °C, the cube orientation strongly developed, while the P-orientation did weakly, even though precipitation occurred before or as soon as recrystallization took place. The results were discussed based on the interaction between precipitation and recrystallization. When the cube component developed during annealing, the copper component in the rolling texture disappeared most rapidly in agreement with the prediction of the strain energy release maximization model.

On the accuracy of the predictions of texture evolution by the finite element technique for fcc polycrystals

Numerical averaging procedures utilizing the finite element technique have been suggested in literature as an improvement over the Taylor averaging scheme for modeling the constitutive behavior of polycrystal aggregates with a known distribution of lattice orientations and a known single crystal constitutive behavior. In this paper, the accuracy of the finite element averaging procedure is evaluated critically by comparing the orientation densities of the α and β -fiber components in rolling textures of fcc metals predicted by both the finite element and the Taylor averaging techniques with the corresponding measurements. It is observed that the finite element predictions are in better agreement with the experiment compared to the Taylor model predictions, especially for the β-fiber texture components. In addition, the sensitivity of the results predicted by the finite element technique to the various geometric and material parameters in the model has been evaluated and discussed.