Microstructure and texture evolution in continuously cooled AA 3004 hot rolled sheet

Abstract

A quantitative study of variations in microstructure and texture evolution in the through thickness direction of industrially hot rolled AA 3004 aluminium alloy has been carried out. The microstructural features of the specimens were examined with the aid of the electron channelling contrast technique in conjunction with an image analysis system. The number of recrystallised grains and the size distributions of coarse and fine intermetallics were measured to evaluate the variation between surface and centre. Significant differences in the number of recrystallised grains and the average size of coarse intermetallics in the through thickness direction of the hotband were observed. After isothermal annealing of the hotband for various times the fine intermetallic area fraction increased and was higher at the centre than at the surface. Quantitative texture analysis was carried out on the specimens and various texture components estimated to characterise the through thickness texture evolution. The proportion of cube texture component was higher near the surface than at the centre and this difference increased after isothermal annealing. Since negligible change occurred in the cube content of the centre specimen, growth of cube grains was deduced to have taken place primarily near the surface region. These observations illustrate that mechanisms of cube texture formation, heterogeneous nucleation of precipitates causing retarded recrystallisation, and Zener drag are evidently applicable even to complex commercial alloys.

MST/1849     

Control of microstructure and earing behaviour in aluminium alloy AA 3004 hot bands

Abstract

Control of earing behaviour at the hot band stage is a critical requirement for successful manufacture of aluminium alloy sheet for beverage cans. The present study has combined production scale experiments with laboratory examinations to investigate the effect of various material and process parameters on microstructure, texture, and earing of the resulting products. It is shown that optimisation of the product is strongly dependent on (i) iron content of the alloy, (ii) ingot homogenisation temperature, (iii) finish hot rolling temperature, and (iv) heating rate during hot band annealing. Earing level after annealing is shown to depend on the balance between cube (+ Goss) texture intensity and the volume of material having almost randomly spread orientations. Pronounced 0/90° earing tendency is usually associated with coarse and elongated grain structures. A model is shown which represents the microstructure–texture evolution as a competition between cube/Goss grains, which nucleate systematically within transition bands, and randomly oriented grains, which nucleate in the vicinity of coarse second phase particles.

MST/1032     

Microstructure and texture evolution during incremental sheet forming of AA1050 alloy

In incremental sheet forming higher limiting strain can be achieved compared to the conventional sheet metal forming process, which results in increased formability. The higher level of strain may be accompanied by non-uniform thinning. Thus, the different sections in a component may undergo different levels of deformation. In the present work a truncated cone of AA1050 H14 alloy was formed using the incremental sheetmetal forming (ISF) technique. The deformation mechanism during ISF was studied by investigating the microstructural and texture evolution in the truncated cone along the thickness of the cone wall. High resolution electron backscatter diffraction was performed at different sections of the formed truncated cone. The results show the formation of subgrains in different sections of the cone. At higher strains, grains become thin and elongated which results in grain fragmentation and formation of small grains. These small grains undergo complete recovery process and new grain boundaries (low and high angle) are formed within the thin elongated grains. Further, the evolution of shear texture shows the evidence of shear mode of deformation during incremental sheet forming. Thus, the presence of through thickness shear could be used for understanding the higher forming limit in the ISF process.

     

Substructure morphology in aluminium alloys AA 3003 and AA 3004

Abstract

The industrial alloys AA 3003 and AA 3004 have been experimentally rolled using a wide range of temperatures and reductions. The substructures obtained were extensively examined, and it is shown that when the rolling reductions are low the relationship between processing parameters and subgrain size (d) follows the well established form d^?m=a+bln Z, where Z is the Zener–Hollomon parameter. As the reduction is increased the orientations of the subgrains to the rolling direction decreases, and the subgrain size also decreases. It is concluded that the existing relationships require modification if they are to be useful in the industrial context.

MST/676     

Microstructure and texture evolution during accumulative roll bonding of aluminium alloys AA2219/AA5086 composite laminates

Accumulative roll bonding of two aluminium alloys, AA2219 and AA5086 was carried out up to 8 passes. During the course of ARB, the deformation inhomogeneity between the two alloy layers results in interfacial instability after the 4th pass, necking of the AA5086 layers after the 6th pass and fracture along the necked regions after the 7th and 8th pass. The EBSD analysis shows deformation bands along the interfaces after 8 passes of ARB. The ARB-processed materials predominantly show characteristic deformation texture components. The weak texture after the 2nd pass results from the combination of a weakly-textured starting AA2219 layer and a strongly-textured starting AA5086 layer. A strong deformation texture forms due to the high imposed strain after a higher number of ARB passes. Subgrain formation and related shear banding induces copper/S components in the case of the small elongated grains, while planar slip leads to the formation of brass component in the large elongated grains.     

Predicting recrystallised volume fraction in aluminium alloy 7050 hot rolled plate

Abstract

An investigation into the partial recrystallisation that occurs during solution treatment of hot rolled thick aluminum alloy 7050 plate has been performed for three alloy variants with different zirconium concentrations. Electron backscattered diffraction has been used to study the grain and subgrain structure in the as rolled condition and after solution treatment. Localised recrystallisation in the grain boundary regions during solution treatment has been largely attributed to the stimulating effect of large intermetallic particles on the boundaries, combined with the low number density of pinning dispersoids close to the grain edges. A model that predicts the dispersoid distribution across a grain has been applied to predict the fraction of recrystallisation after solution treatment. It has been demonstrated that the recrystallised fractions predicted by the model show good agreement with those measured experimentally. Example calculations are presented showing the predicted effect of the zirconium level, homogenisation conditions, and subgrain size on the recrystallised fraction.     

Structure,anisotropy, and properties of hot rolled AA 5083 alloy

Abstract

The changes in structure and substructure occurring during homogenisation and hot rolling of an Al–5Mg alloy (AA 5083) have been investigated. It is shown that a homogenisation treatment is beneficial and that the resulting structure can be related to processing parameters. The results suggest that the substructure morphology is dependent upon the total strain, but this has not been quantified. The development of texture was also studied and it is shown to be almost invariant with temperature, but strongly strain dependent. The anisotropy so produced yielded plastic strain ratios that were found to be strongly dependent upon the rotated copper texture intensity. The deep drawing behaviour of the hot rolled sheet was investigated by employing cupping tests and it is shown that a relationship exists between the earing value and the subgrain size.

MST/I086     

Recrystallisation and texture in hot deformed aluminium alloy 7010 thick plates

Abstract

The recrystallisation behaviour and its effect on the crystallographic texture during solution heat treatment of thick aluminium alloy 7010 plates has been studied both on commercially hot rolled plates and on laboratory specimens deformed in plane strain compression. In addition to X-ray macrotexture analysis, individual grain orientation measurements within the recovered subgrains and the recrystallised new grains were performed by means of electron backscattering diffraction. Significant recrystallisation takes place during the solution treatment with almost no change in the macrotexture. This behaviour is explained by the balancing effect of randomisation of the texture during recrystallisation and texture sharpening within the recovered matrix regions.

MST/3433     

3004铝合金晶格和织构演化的原位X射线衍射研究

为探究3004铝合金板材在拉伸变形过程中晶粒取向变化和晶格应变行为,明确两者在塑性变形过程中的竞争机制和作用,本文首次将原位拉伸方法用于铝合金织构演化和晶格应变行为的研究中,利用试验装置对3004铝合金进行定量应变拉伸,并在不同变形量下对样品进行X射线衍射物相和织构测试分析.实验结果表明:样品在弹性变形区晶格常数随应变...     

Breakup of texture alignment and reduction of roping in AA6111 aluminium alloy

The evolution of crystallographic texture in AA6111 automotive aluminium alloy during thermo-mechanical sheet processing has been investigated. It was confirmed that the formation of a band-like structure of {001}<100> and {011}<100> textures is the determining factor for roping, while the roping level is controlled by the length of the alignment. The texture is cumulatively developed through the entire rolling process, but can be significantly shortened by an intermediate batch anneal. During annealing, the band-like structure is broken by the nucleation and growth of other orientations. Intermediate annealing also coarsens intermetallic particles, which reduces any particle pinning effects and promotes particle stimulated nucleation during the final solutionising treatment, leading to a randomised texture, which minimises roping in the final T4 temper.     

Dynamic recrystallisation and dynamic precipitation in AA6061 aluminium alloy during hot deformation

Abstract

Deformation behaviour of AA6061 alloy was investigated using uniaxial compression tests at temperatures from 400 to 500°C and strain rates from 0·01 to 1 s^?1. Stress increases to a peak value, then decreases monotonically until reaching a steady state. The dependence of stress on temperature and strain rate was fitted to a sinh-Arrhenius equation and characterised by the Zener–Hollomon parameter with apparent activation energy of 208·3 kJ mol^?1. Grain orientation spread analysis by electron backscattered diffraction indicated dynamic recovery and geometrical dynamic recrystallisation during hot compression. Deformation at a faster strain rate at a given temperature led to finer subgrains, resulting in higher strength. Dynamic precipitation took place concurrently and was strongly dependent on temperature. Precipitation of Q phase was found in the sample deformed at 400°C but none at 500°C. A larger volume fraction of precipitates was observed when samples were compressed at 400°C than at 500°C.     

Comparison of the texture evolution in cold rolled DC and SC AA 5182 aluminum alloys

The hot bands of direct chill cast (DC) and strip cast (SC) AA 5182 aluminum alloys were annealed at 454 °C for 3 h, and then cold rolled to different reductions. The ODFs of the cold rolled samples were determined by X-ray diffraction in order to compare the texture evolution of DC and SC AA 5182 aluminum alloys during rolling. The texture volume fractions were computed by a new method, in which the Euler space representing all possible crystallographic orientations in rolling was subdivided into the cube, r-cube, Goss, r-Goss, β fiber, and random orientation regions based on the slip pattern combined with the characteristics of microstructure and texture. Empirical formulae of the texture volume fractions and true strain were constructed to predict the texture of cold rolled DC and SC AA 5182 aluminum alloys. The results show that the processing method (DC vs. SC) strongly affects the texture after annealing at 454 °C and the texture evolution during the subsequent rolling.     

Microstructure evolution in aluminum alloy AA 2014 during multi-layer friction deposition

How microstructures evolve in heat-treatable aluminum alloys during multi-layer friction deposition is an intriguing question. The current work shows that the process invariably leads to overaging of strengthening precipitates in such materials as alloy 2014. The problem can be overcome using a solution treatment, but it can lead to other problems such as abnormal grain growth. Based on these findings, it appears that the benefits of friction deposition cannot be fully realized in heat-treatable aluminum alloys.     

热轧过程中高纯钴微观组织及织构演变

金属钴具有同素异构转变特性。为探究热轧工艺对高纯钴的微观组织及织构演变规律的影响,对纯度为99.99%(质量分数)的高纯钴进行500 ℃(高于同素异构转变温度)下的热轧,并采用电子背散射衍射(EBSD)技术对样品进行表征。结果表明:初始态板材由密排六方相(HCP相)和面心立方相(FCC相)构成,且以HCP相为主;HCP相晶粒的晶体取向较为集中,而FCC相晶粒的晶体取向较为分散;HCP相中的相变孪晶和FCC相中的退火孪晶含量较高。经过热轧,不同道次下的水冷板材中仍含有HCP相和FCC相,HCP相和FCC相在不同轧制板材中含量略有不同,但FCC相的相对含量均高于HCP相;HCP相晶粒的细化效果尤为显著。两相的小角度晶界含量较初始态大幅度上升,大角度晶界含量大幅度下降;轧制水冷板材中HCP相形成了特殊的择优取向,{0001}基面法向偏离ND方向朝向RD方向35°,且{10-12}取向较为分散;而FCC相呈现出较为随机的晶体取向特征。     

Microstructure,texture evolution and mechanical properties of cold rolled Ti-32.5Nb-6.8Zr-2.7Sn biomedical beta titanium alloy

Ti-32.5 Nb-6.8 Zr-2.7 Sn(TNZS,wt%) alloy was produced by using vacuum arc melting method,followed by solution treatment and cold rolling with the area reductions of 50% and 90%.The effects of cold rolling on the microstructure,texture evolution and mechanical properties of the experimental alloy were investigated by optical microscopy,X-ray diffraction,transmission electron microscopy and universal material testing machine.The results showed that the grains of the alloy were elongated along rolling direction and stress-induced α' martensite was not detected in the deformed samples.The plastic deformation mechanisms of the alloy were related to {112} 111 type deformation twinning and dislocation slipping.Meanwhile,the transition from γ-fiber texture to α-fiber texture took place during cold rolling and a dominant {001} 110_(α-fiber) texture was obtained after 90% cold deformation.With the increase of cold deformation degree,the strength increased owing to the increase of microstrain,dislocation density and grain refinement,and the elastic modulus decreased owing to the increase of dislocation density as well as an enhanced intensity of {001} 110_(α-fiber)texture and a weakened intensity of {111} 112_(γ-fiber)texture.The 90% cold rolled alloy exhibited a great potential to become a new candidate for biomedical applications,since it possesses low elastic modulus(47.1 GPa),moderate strength(883 MPa) and high elastic admissible strain(1.87%),which are superior than those of Ti-6 Al-4 V alloy.     

Modeling texture evolution during hot rolling of magnesium alloy AZ31

The texture evolution during hot rolling of the magnesium alloy AZ31 is simulated using a visco-plastic self-consistent model including crystallographic slip, twinning and recrystallization. This combined model is shown to capture the main features observed in mechanical tests and in X-ray diffraction measurements of the texture. The model is implemented in the commercial finite element code ABAQUS/Explicit^®, and hot rolling is simulated. Although the strain field exhibits considerable gradients over the sheet thickness and strong shear components at the sheet surface, the basal texture, as it is commonly observed in rolled magnesium sheets, predominates over the whole thickness.     

Microstructure development in hot deformed AA6082

Age hardenable aluminium alloys are suitable for hot deformation at temperatures between 300 and 600 °C, depending on the alloy and on the process. During thermo mechanical processes, dynamic and/or static restoration mechanisms take place. In this work, hot compression tests of hot rolled AA6082 and of a hot extruded AA6082 were carried out by means of a Gleeble^® 1500 thermo-mechanical system, between 450 and 550 °C and at 0.1-10 s⁻¹ of strain rate followed by fast cooling. The materials were thermo-mechanically processed before hot deformation to transform the complex initial microstructure into a fully recrystallized microstructure. Some compression tests of non recrystallized samples were carried out for comparison. All the samples were examined using electron backscatter diffraction (EBSD), followed by a determination of grain size and subgrain size distributions as well as of the local misorientation distribution. The as received samples showed a duplex microstructure consisting of elongated grains oriented in the rolling and extrusion directions, and some small recrystallized grains. The main restoration mechanism for all the materials is shown to be dynamic recovery, and the Zener-Hollomon parameter, as well as the flow stress was correlated to the subgrain size. The hot rolled material flow behaviour was sensitive to the initial microstructure, and geometric dynamic recrystallization was found.     

Effect of preheat treatment on ingot structure and recrystallisation of brass component of rolling texture in hot rolled AA 5182

Abstract

Two different preheating treatments were used to vary the Al₆ Mn dispersoid characteristics in AA 5182. High temperature followed by slow cooling produced coarse, needlelike dispersoids which allowed rapid recrystallisation following hot rolling, whereas a low temperature preheat produced afine dispersion of low aspect ratio particles which retarded recrystallisation. Long, unrecrystallised bands persisted in the hot rolled material subected to the low temperature preheat even after holding for 24 h at the final pass temperature. Micro-orientation determinations within the bands showed that they were predominantly of the brass (Bs) orientation, {110}〈112〉, confirming the results of X-ray bulk texture analyses. The results are considered conclusive evidence of the widely reported higher resistance to recrystallisation of the Bs orientation compared with other orientations in rolled high stacking fault energy fcc metals. The Bs oriented bands could be removed by annealing at a temperature substantially greater than that experienced in the final hot rolling pass.

MST/1475     

Through-thickness texture gradient in AA 7055 aluminum alloy

Through-thickness texture gradient in AA 7055 aluminum alloy rolled plate has been investigated using the electron back-scattered diffraction (EBSD) technique. Quantitative analyses of texture in five layers from the surface to the center of the plate were performed. A pronounced texture variation through the plate thickness was found. In the center layer, a typical β fiber texture running from {112} <111> orientation through {123} <634> orientation to {011} <211> orientation was found. Near the surface, in contrast, shear type textures including {001} <110> orientation, {112} <110> orientation and {111} <110> orientation were dominating. In particularly, when the shear type textures reached the maximum in both intensity and content, the β fiber became minimums.