Effects of homogenisation treatment on microstructure and grain refinement of Al–1.2Mn alloy

The effects of a homogenisation treatment on precipitation, recrystallisation, grain refinement and texture in an Al–1.2Mn alloy were investigated. Based on hardness and electrical conductivity measurements, a precipitation–recrystallisation diagram was generated, which described the sequence of recrystallisation and precipitation. The results showed that recrystallisation was significantly retarded during the annealing treatment for the cold-rolled alloys with a supersaturated solid solution or with dense pre-existing dispersoids. If precipitation occurred prior to recrystallisation, the precipitates caused a strong resistance to recrystallisation, resulting in a coarse and elongated grain structure with a dominant normal direction-rotated cube texture. In contrast, when recrystallisation was completed before precipitation, recrystallisation was little affected by the precipitates, leading to a fine-grained structure with a weak cube texture.     

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.     

Secondary recrystallisation of MA 957 oxide dispersion strengthened ferritic superalloy

Abstract

Secondary recrystallisation has been studied in MA 957 oxide dispersion strengthened ferritic superalloy following heat treatment at a temperature of ~1320°C. Selected area channelling patterns in the scanning electron microscope were used to characterise the crystallographic texture of grains of large aspect ratio produced by zone annealing and microbeam electron diffraction was used to determine the orientations of submicrometre, equiaxed grains behind the (secondary) recrystallisation front. MA 957 exhibits a dominant 〈110〉 texture in the as extruded condition, but this texture is notably absent after recrystallisation. At high zoning speeds the material displays a 〈113〉 texture, but an increasing proportion of 〈111〉 texture component is evident as the zoning speed is reduced. The texture development can be tentatively rationalised in terms of the influence of solute segregation processes and grain orientation on interfacial mobility.

MST/1555     

Mg–3Al–1Zn alloy strips processed by electroplastic differential speed rolling

The effect of reduction per pass on the mechanical properties, microstructure and texture evolution of Mg–3Al–1Zn magnesium alloy strips processed by electroplastic differential speed rolling has been investigated. With increasing reduction per pass, the mechanical properties of the rolled strips increase. Both the shear effect and the current pulses play an important part in modifying the microstructure and texture by promoting dynamic recrystallisation. During dynamic recrystallisation, nucleus tends to nucleate in the vicinity of the shear bands. And as the progress of dynamic recrystallisation, shear bands are gradually consumed by the newly nucleated grains and become nearly indistinguishable. The athermal effect of current pulses plays an important role in promoting dynamic recrystallisation.     

Evolution of rotated Brass texture by cross rolling: implications on formability

In the present work, the possibilities of tailoring crystallographic texture via cross rolling are presented. It is shown that a strong rotated Brass texture develops upon cross rolling in aluminium alloys which also remains intact during the subsequent recrystallisation annealing treatment. The governing mechanisms behind the evolution of deformation and recrystallisation texture are discussed in terms of effect of strain path on stability of deformation texture components and strain-induced boundary migration mechanism, respectively. In addition, the likelihood of rotated Brass texture having a positive effect on formability is discussed in terms of sluggish cross-slip criteria as the rotated Brass texture presents a unique scenario where cross-slip is inhibited along all the three principal directions.     

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.     

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.     

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     

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.     

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.     

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     

Stored energy in can body aluminium alloy after cold rolling and stress relieving

Abstract

Information on the stored energy after cold deformation and stress relieving would provide a greater understanding of the mechanism that controls the primary recrystallisation in deformed metals. Stored energy as a function of crystal orientation of 88% cold rolled and stress relieved can body aluminium alloy is calculated using the diffraction peaks from X-ray analysis. The obtained stored energy values are presented in the form of a stored energy distribution function on Euler angle space similar to the orientation distribution function. The stored energy along the β fibre that characterises the deformation texture and cube recrystallisation texture components is discussed in detail. A significant reduction of stored energy for the cube texture component after stress relieving is observed.     

Development of microstructures of high grain aspect ratio during zone annealing of oxide dispersion strengthened superalloys

Abstract

Two extruded bars of the nickel base mechanically alloyed materials MA 6000 and MA 760 have been zone recrystallised in a calibrated gradient furnace. Selected area channelling patterns in the scanning electron microscope have been employed to study the crystallographic texture of the grains of large aspect ratio produced by zone annealing, and microbeam electron diffraction has enabled the orientations of the submicrometre sized equiaxed grains in the material behind the (secondary) recrystallisation front to be studied. In both alloys a curved secondary recrystallisation interface is observed, with the surface recrystallising at a lower temperature than the interior. This is considered to result indirectly from the strain gradients occurring during extrusion. A <110> texture is present, and reasons for this are discussed. In MA 6000 progressive grain rotation towards <110> has been measured behind the recrystallisation interface, although this is not observed in MA 760 as it transforms at a lower temperature. Quenching experiments have shown that nucleation of secondary recrystallisation occurs at temperatures higher than that at which the recrystallisation interface grows at the zoning speed employed. It is suggested that the microstructure develops via the thermally activated unpinning of interfaces which have mobility advantages.

MST/1948     

Microstructure characterisation of Fe–21Cr–15Ni–Nb–V non-magnetic austenitic stainless steel during hot deformation

Hot deformation behaviour of Fe–21Cr–15Ni–Nb–V stainless steel was investigated by isothermal compression in the temperature range of 950–1150°C with a strain rate of 0.01–10?s^?1. The results showed that complete recrystallisation occurred beyond 1050°C, resulting from the pinning effect of (Nb, V)(C, N). The nucleation of dynamic recrystallisation (DRX) was performed by the bulging, sub-grain swallowing and twinning mechanism. With increasing strain rate, new twinning was transformed into the Σ3 regeneration mechanism in the partial DRX region, while an opposite transformation was observed in the complete DRX region. In the partial recrystallisation region, grain rotation resulted in the formation of 110 orientation. In the complete recrystallisation region, the texture tended to distribute randomly at a high strain rate, and the grain growth was accompanied by the emergence of stable 100 orientation.     

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.     

Texture modification of magnesium alloys during electropulse treatment

ABSTRACT

Differential speed rolling (DSR) at room temperature has been carried out on two Mg–1Gd and Mg–1Zn–1Gd rare-earth-containing magnesium alloys with different thickness reductions. The cold-rolled samples were selected to investigate the microstructure and texture evolution during the electropulse treatment (EPT). Both grain refinement and texture modification have been achieved for the three cold-rolled samples, which were accompanied by nucleation and nuclei growth during EPT. The recrystallisation process could be attributed to enhanced climb activity of dislocations by EPT, which produces not only a thermal effect but also an athermal effect. Compared with Mg–1Gd, Mg–1Zn–1Gd shows a smaller recrystallisation rate, which should be related to the solute segregation and could be one of the reasons for the texture modification of the alloy.

This paper is part of a themed issue on Materials in External Fields.     

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     

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     

Texture evolution in stainless steel processed by selective laser melting and annealing

This work analyses the texture and microstructure gradients emerging in a 316L stainless steel processed by selective laser melting, using an island scan strategy, followed by annealing. Laser processing leads to the alignment of different crystallographic directions with the build direction at the mid and top layers, as well as to gradual structural coarsening. Annealing triggers discontinuous recrystallisation at highly strained regions, such as grain boundaries and laser track centre lines, resulting in the onset of new texture gradients. The development of the mentioned texture gradients is rationalised based on a competition between thermal gradient-driven growth and epitaxial growth.     

Interaction between precipitation,normal grain growth,and secondary recrystallisation in austenitic stainless steel containing particles

Abstract

With the aid of various complementary methods of microstructural analysis, the precipitation, grain growth, and secondary recrystallisation behaviour of an 15Cr–15Ni–1·2Mo–Ti–B (wt-%) austenitic stainless steel were studied over prolonged periods of time in the temperature range 600–1300°C. The experimental results showed that several types of precipitates were present in the material, and that the dissolution temperatures of each of these correlated with the type and extent of grain growth which was observed. It was, therefore, concluded that in the present study secondary recrystallisation was caused directly by the interaction of precipitates with grain boundaries. Furthermore, secondary recrystallisation produced a strong, predominantly {122{ 〈012〉 texture which has not previously been reported.