Influence of particles on recrystallisation textures and microstructures of aluminium alloy 3103

Abstract

The evolution of recrystallisation textures in the commercial aluminium alloy 3103 has been investigated by means of a three-dimensional orientation distribution function (ODF) analysis. The global texture measurements were supplemented by local texture measurements by means of the electron backscattering pattern (EBSP) technique in SEM and optical microscopy, inparticular grain size measurements. The evolution of recrystallisation textures was determined by the competition between particle stimulated nucleation (PSN) and nucleation from cube bands. Precipitated particles were found to have a higher retarding effect on the nucleation from deformation zones around particles than on the nucleation from cube bands. The result of this is a strong cube texture and a large grain size in cases of a strong precipitation reaction. This phenomenon has also been discussed theoretically in terms of a semiquantitative model.     

Annealing behaviour of dilute aluminium alloys following hot deformation

Abstract

The microstructure and texture of three dilute aluminium alloys after hot deformation and annealing was assessed; In particular, the influence of deformation temperature, strain rate, and strain on the annealed texture was examined, as well as the effect of alloy composition. The microstructures of the commercially pure materials studied (Al, Al+1%Mn and Al+1%Mg) varied in the volume fraction of coarse intermetallic particles, the type of dispersoid present, and the level and type of solute in solid solution. Furthermore, the initial stages of recovery and recrystallisation were studied in detail for one of the alloys (commercially pure Al). It was found that the main recrystallisation texture component was the cube and its strength, as well as the recrystallised grain size, depended strongly on the deformation strain. The deformation strain rate and temperature, and the alloy composition also strongly influenced the grain size and cube texture strength. These results are discussed in the context of current theories for cube nucleation within cube bands in the hot deformed microstructure. The present work was carried out as part of a wider research programme, partially supported by the European Union (Brite/Euram funded), to develop micromechanical models to describe the evolution of microstructure and texture during hot deformation and annealing of aluminium alloys.

MST/3376     

Control of annealing texture and earing in non-hardenable aluminium alloys

Abstract

Factors affecting textures in non-hardenable aluminium alloys are considered on the basis of published results and some new experimental results. Emphasis is placed on conditions relevant to industrial scale rolling and annealing of sheet products. The most commonly observed texture components in these alloys are summarised, together with available evidence regarding their origins. Hot rolling conditions have a powerful effect on subsequent annealing textures, which is attributed to the microstructural state of the material before cold rolling. This can influence the relative frequency of different nucleation mechanisms. Heat treatment of the hot rolled band can also bring about marked changes in texture and earing for the same reason. The effect of cold rolling reduction on texture is complex and depends on the initial microstructure; increasing reduction promotes an increasingly heterogeneous substructure. The main impurity in these alloys is iron, which plays several different roles in controlling texture and earing level. Iron, both in solid solution and as coarse precipitates, can weaken the cube texture and promote 45° earing tendency. However, fine scale precipitation in the deformation substructure before recrystallisation may contribute to a strengthening of the cube texture. For high contents of iron and heavy rolling reductions, where continuous recrystallisation occurs, the rolling texture is retained or may even become strengthened. Influences of silicon, manganese, and magnesium are also discussed.

MST/1295     

Recrystallisation textures in cold rolled low carbon steel containing ferritic and bainitic microstructures

Abstract

Low carbon steel strip was heat treated to generate four different starting microstructures (fine and coarse polygonal ferrite, acicular ferrite and bainite) for investigating their influence on texture development during cold rolling and annealing. The starting materials were cold rolled to 50–90% reduction and annealed for various times in the temperature range 853–953 K. The resultant microstructures and textures were examined mainly by electron backscatter diffraction and X-ray diffraction. The initial microstructure strongly influenced the crystallographic rotation paths during cold rolling, whereby high strain deformation generated strong {223}〈110〉 texture components in the polygonal ferritic microstructures, whereas a strong {001}〈110〉 texture was produced in the acicular/bainitic microstructures. Subsequent annealing generated, to varying degrees, the classic {111}〈uvw〉 (γ-fibre) recrystallisation texture in all materials. Unexpectedly, coarse polygonal ferrite produced the strongest γ-fibre recrystallisation texture after 70–90% cold rolling reduction. Based on arguments involving the effect of carbon in solution, initial grain size and deformation textures on recrystallisation texture development, it was shown that a strong γ-fibre texture can indeed be generated in coarse polygonal ferrite.     

Recrystallised grain size of commercial purity aluminium after hot torsion within steady state regime

Abstract

Hot deformation within the steady state regime of commercial purity aluminium has been carried out under wide ranges of deformation parameters: temperature, strain, and strain rate. The microstructure developed after deformation exhibited dynamically formed grains having volume fraction increasing with strain and of size inversely dependent on flow stress. The effects of the parameters of deformation and of the annealing temperature after deformation on statically recrystallised grain size and on the rate of grain boundary migration during recrystallisation were studied and can be satisfactorily described by equations in which each of the variables is considered to act independently. The effects of the deformation parameters on the grafnsize produced after static recrystallisation are interpreted in terms of their influence on the number of dynamically formed grains that can act as pre-existing nuclei. A decrease in the final recrystallised grain size with an increase in annealing temperature, which may be related to the number of dynamically formed grains that become viable nuclei, was observed. The growth rate during recrystallisation was found to decrease with increasing time, probably as a result of the distribution of stored energy within the deformed structure.

MST/1169     

On the cold rolling textures in some fcc Ni–W alloys

The development of thin, mechanically stronger and highly cube textured substrates is of great technological importance for increasing the engineering current density of coated superconductors. Due to the development of a strong recrystallisation cube texture and improved strength, Ni–W alloys are good candidate substrate materials for the development of coated superconductors. It is well known that the recrystallisation cube texture is strongly related to the rolling texture, which in turn is related to the alloying content, temperature of deformation, etc. In the present paper, we report the copper-type to brass-type texture transition in the rolling texture of cold rolled fcc Ni_1−xW_x alloys at W contents >5 at.%. The possible reasons for the above texture transition and the consequences on recrystallisation texture are discussed.     

Microstructure and texture of aluminium alloys 3105 and 3015 during cold rolling and annealing

Abstract

The microstructure and texture of industrially produced hot bands of direct chill (DC) cast AA 3105 and continuous cast (CC) AA 3015 during cold rolling and annealing have been studied. The textures were determined using an X-ray diffraction technique and then analysed using orientation distribution functions. The Copper, Brass, and S texture components were the major deformation texture components for both the DC and CC materials after the same cold rolling process. After an annealing process, the Cube component was found to be the major recrystallisation texture component for AA 3105 DC material. In contrast, it was difficult to obtain the Cube texture component in AA 3015 CC material after cold rolling followed by annealing. Instead, the P orientation {011} 〈566〉 with Euler angles of (?₁,Φ,? ₂) = (60°,45°,0°/90°) was found to be the major recrystallisation texture component of the AA 3015 CC material.     

Effect of pretreatment and texture on recovery and recrystallisation in Al–4·5Mg–0·7Mn alloy

Abstract

The development of recovery and recrystallisation in cold rolled Al–4·5Mg–0·7 Mn (designated AA 5083) was analysed metallographically, by measuring hardness and electrical conductivity, and by means of texture analysis. The precipitation state and the initial texture were varied using appropriate pretreatments before cold rolling in order to study the influence of these parameters on kinetics and texture evolution during deformation, recovery, and recrystallisation. Finally, the results obtained were compared with those obtained for conventionally produced material.

MST/1960     

Heterogeneous deformation and recrystallisation of iron base oxide dispersion strengthened PM2000 alloy

Abstract

The recrystallisation behaviour of PM2000 oxide dispersion strengthened ferritic alloy has been investigated for tube specimens which had been cold deformed after extrusion. The evolution of the recrystallisation temperature, defined as the minimum temperature at which the specimen begins to recrystallise, has been studied in detail as a function of the level of deformation. The microstructure was characterised using optical and transmission electron microscopy, together with microhardness measurements, and local texture measurements obtained using the electron backscattering pattern technique. The results can be interpreted if it is assumed that any procedure that produces a heterogeneous microstructure, stimulates recrystallisation. In this sense, larger strain gradients lead to more refined and more isotropic grain structures. The way in which these results can be exploited for commercial applications is discussed.     

Effect of roll pass schedule on through thickness texture development in Al–Mn alloy

Abstract

During hot rolling a texture gradient is developed through the thickness of the slab. This is directly related to the different strain paths experienced by the material between the surface and the centre plane. The difference in strain path not only affects the texture, but can also give differences in stored energy though the thickness, which in turn affects the recrystallisation kinetics and ultimately the recrystallisation texture. The strain path is further complicated when a number of roll passes are involved, since the material is subjected to more complex strain paths. In the current investigation the effects of roll pass schedule (rolling direction, i.e. reverse rolling or continuous rolling) on the texture development during deformation and subsequent annealing have been characterised for an Al-1%Mn alloy. The study has shown that the texture of the surface region of the slabs is dependent on the roll pass schedule. This effect is at a maximum in the near surface region, although the effect of roll pass schedule on the recrystallisation kinetics is at a maximum 20% of the half thickness below the surface of the slabs.     

Recrystallisation kinetics of TWIP steel: interface velocity and stored energy

Abstract

In the present article, a modular phase transformation kinetics model has been employed to describe the static recrystallisation behaviour of a high Mn (25 wt-%) twinning induced plasticity steel just after hot deformation. The modular recrystallisation model is based on site saturation with preferential distribution of nuclei, interface controlled growth and impingement of growing particles. The model prediction has been validated with the experimental recrystallisation data of twinning induced plasticity steel. The experimental data were also modelled using Johnson–Mehl–Avrami kinetics based on random distribution of nuclei, which showed worse prediction as compared to the modular transformation kinetic model, thereby indicating the possibility of preferential nucleation around the defect sites. The rate of recrystallisation estimated from the measured fraction recrystallisation decreases sharply within a small recrystallised fraction. The interface migration velocity (interface between the recrystallised grains and the deformed matrix) was estimated from the analytical model. The interface velocity decreases sharply within initial small recrystallised fraction. The calculated stored energy of deformation, from the estimated interface velocity and mobility of the interface, suggests an inhomogeneous distribution within the deformed matrix.     

Mechanism of cube grain nucleation during recrystallization of deformed commercial purity aluminium

Cube texture is a sharp recrystallization texture component infcc metals like aluminium, copper, etc. It is described by an ideal orientation i.e. (100) (100). The subject of cube texture nucleation i.e. cube grain nucleation, from the deformed state of aluminium and copper is of scientific curiosity with concurrent technological implications. There are essentially two models currently in dispute over the mechanism of cube grain nucleation i.e. the differential stored energy model founded on the hypothesis proposed by Ridha and Hutchinson and the micro-growth selection model of Dugganet al. In this paper, calculations are made on the proposal of Ridha and Hutchinson model and the results are obtained in favour of the differential stored energy model. It is also shown that there is no need for the micro-growth model.     

Influence of transformation induced recrystallisation on hot rolling textures of low carbon steel sheet

Abstract

A series of hot rolling textures of steel sheet with different compositions and hot rolling parameters have been compared. The observed hot rolling textures all belonged to a limited number of different types. These types seemed to depend on the composition, the hot rolling parameters, and the local deformation mode. The influence of these hot rolling textures on the properties of commercial sheet steels after cold rolling and continuous annealing is critically evaluated. For steels with a low content of high temperature precipitates, the texture and microstructure after intercritical hot rolling often appeared to be the result of a transformation induced recrystallisation process with a specific nucleation mode. Understanding of the nature of this type of recrystallisation may facilitate an improvement in the material properties by optimisation of the hot rolling texture.

MST/1327     

Texture development in high strength aluminium alloys

Abstract

Texture development during the thermomechanical processing of high strength aluminium alloys is reviewed. The alloys dealt with include both conventional heat treatable alloys, and unconventional materials such as rapidly quenched alloys and metal-matrix composites. The processing routes considered include hot and cold rolling, extrusion, forging, recrystallisation, and superplastic deformation. The information is presented as (111) pole figures and orientation distribution functions, in order to illustrate the much greater degree of detailed information that can be extracted from the latter method of analysis. The implications of texture development are considered by examining the effects that texture can have on tensile property anisotropy and fatigue and fracture behaviour.

MST/1292     

Nucleation and growth during recrystallisation of aluminium alloys investigated by local texture analysis

Abstract

This paper presents a systematic survey on the formation of recrystallisation textures in cold rolled Al alloys. In particular, the nucleation of new grains in cube bands, grain boundaries, shear bands, and the deformation zones around large pProceedings of Conference 'Texture on a Mircoscale' as well as their subsequent growth into the deformed matrix are examined and discussed in the context of their contribution to the final recrystallisation textures. In addition to X-ray macrotexture analysis, particular attention is focused on the determination of local orientations by electron diffraction either in the transmission electron microscope (microbeam electron diffraction) or, at later stages of recrystallisation, in the scanning electron microscope (electron backscattered diffraction). A combination of these complementary techniques for orientation determination with increasing spatial resolution yields much more valuable information on the underlying mechanisms of recrystallisation than is accessible by the sole use of the individual techniques.

MST/3676     

Microstructure and texture evolution in hot rolled AA 3004 aluminium alloy

Abstract

The evolution of microstructure and texture in industrially hot rolled AA 3004 aluminium alloy has been studied. Specimens were subjected to isothermal annealing treatments and the recrystallisation kinetics was determined via measurement of changes in hardness at surface and centre locations. Metallographic examination of specimens was performed using electron channelling contrast. With the aid of an image processor, the Mg₂Si precipitate count and size distributions were obtained. A significant increase in the number of precipitates was observed to occur after the completion of recrystallisation. Quantitative texture analysis was performed on the tapered specimens to characterise the through thickness effect. The quantity of cube texture component was shown to be higher at the surface than at the centre location and decreased with increasing exit temperature of the hotband.

MST/1564     

Effect of silicon on recrystallisation of V–Ti microalloyed steel

Abstract

The dynamic recrystallisation (DRX) and static recrystallisation (SRX) behaviours of three V–Ti microalloyed steels were studied by the analysis of the true stress–strain curves and the stress relaxation curves under different deformation conditions. The results of DRX showed that deformation activation energy Q_def, peak stress and peak strain increased, as a result of the solute strengthening and dragging effect due to Si. The results of SRX showed that Si increased the SRX activation energy Q_SRX. The solute retardation parameter for static recrystallisation of Si was calculated. Based on the SRX results, to quantify the drag effect of Si and V, a new model was proposed to describe the time for 50% recrystallisation (t_0·5), which was tested and verified by previously published data on similar steels. Precipitation during recrystallisation could lead to a lower value of the Avrami exponent.     

Dynamic recrystallisation in hot deformed oxide dispersion strengthened MA956 and MA957 steels

Abstract

The hot deformation behaviour of the oxide dispersion strengthened stainless steels MA956 and MA957 has been studied. The alloys are made by a mechanical alloying process which leaves them in a very fine grained, cold deformed state immediately after consolidation. It is found that deformation is accompanied by dynamic recrystallisation, even when the deformation temperatures are far less than the ordinary recrystallisation temperatures of the two alloys. These and other results on the strength and anisotropy of the alloys are interpreted in terms of their microstructures.

MST/3043     

冷轧形变量对异步轧制高纯铝箔织构的影响

应用取向分布函数(ODF)研究和分析了异步轧制高纯铝箔的形变织构和再结晶织构.结果表明:异步轧制高纯铝箔的形变织构除了C{112}<111>、B{110}<112>和S{123}<634>织构组分外,还有较强的CubeND{001}<110>和{102}织构.异步轧制高纯铝箔的再结晶织构由强的立方织构{001}<100>和弱的R{124}<211>织构组成.随着形变量的增加,异步轧制高纯铝箔的形变织构和再结晶织构呈现规律性的变化,{102}织构减少,S织构先增后减,速比较小时C织构近线性减少,速比较大时C织构则先增后减.异步轧制高纯铝箔的退火样品中有很强的立方织构,这与异步轧制提高高纯铝箔的形变储能有关,形变量过大时,立方织构随形变量的增加急剧减少.{102}织构有利于再结晶立方织构的加强.     

Formation of {111} fibre texture in recrystallised aluminium sheet

Abstract

The deep drawability of commercial purity aluminium sheets is improved by introducing a (in fcc materials rather unusual) {111} fibre texture in the sheet surface layers. An additional step of warm rolling after the conventional hot and cold rolling leads to the formation of a pronounced shear texture in the sheet surface layers. During the final recrystallisation annealing, the desired {111} texture prevails at the expense of the other shear texture components. The present paper aims to clarify the mechanisms of the formation of {111}∥ND orientations during both warm rolling and recrystallisation. The effect of the {111} surface texture on the plastic anisotropy of the resulting sheets is discussed.