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.     

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.     

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     

On the origin of recrystallization textures

The development of recrystallization textures has been debated for the past 50 years. Essentially the rival theories of evolution of recrystallization textures i.e. oriented nucleation (ON) and oriented growth (OG) has been under dispute. In the ON model, it has been argued that a higher frequency of the special orientation (grains) than random occur, thus accounting for the texture. In the OG model, it has been argued that the specially oriented grains have a high mobility boundary and thus can migrate faster and grow to a larger size as compared to random orientations thus contributing to the final recrystallization texture. In FCC metals and alloys like aluminium, cube orientation [(001) 〈100〉] is the recrystallization texture component. In the classic OG model, cube orientation is supposed to be misoriented fromS-orientation [(123) ] which is a deformation texture component by a 40° about 〈111〉 relationship which is supposed to be a high mobility boundary leading to faster growth of cube grains. Stereographic calculations and analytical calculations are presented in this paper to the effect that theS-orientation (123) is not misoriented from cube (100) 〈001〉 by 40° 〈111〉 whereas another deformation texture component (123) which is termed theR-component is misoriented from cube component by 40° 〈111〉,R-component is also seen in deformation textures of aluminium and hence the classic OG model remains valid with respect to theR-component.     

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     

A study of precipitation and recrystallization behaviour of aluminium alloy AA1235

The recrystallization behaviour of 92% cold rolled commercial pure aluminium has been studied. Annealing was done at different conditions to evaluate the effect of recrystallization temperature and time on the microstructure and texture of the alloy along with a study of subsequent precipitation. Variation of orientation between grains has been studied by the orientation imaging microscopy (OIM). During precipitation, cube component {001}<100> has dropped and rolling texture component has increased comparatively. Recrystallization texture is the combination of cube, rolling and random texture. However, during grain growth strong cube grains have formed. A significant number of dislocations are present during grain growth owing to the pinning effect of Al₃Fe particles.     

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     

中间退火及成品退火速率对高压阳极铝箔微观组织的影响

采用不同中间退火温度及成品退火速率对高压阳极铝箔进行处理,并利用EBSD及XRD技术分析其微观组织结构,尤其是织构的变化规律。结果表明,中间退火温度对后续成品退火中形成立方织构起到了关键作用,这可能是由于低温中间退火保留了大量的形变储能,为成品退火时立方织构的形成增加了形核核心。同时,低的中间退火温度造成立方织构较理想位置偏转程度更大。随着成品退火加热速率的增大,铝箔再结晶分数及再结晶晶粒尺寸逐渐减小,这是由于退火加热速率的增大(低于临界加热速率),缩短了晶界迁移的时间,减缓了再结晶的发生。     

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     

Nucleation of recrystallization in compressed aluminium: studies by electron microscopy and Kikuchi diffraction

Following the earlier investigation of recrystallization of aluminium by Bellier and Doherty [1] by transmission Kossel diffraction, the details of the nucleation process were studied by transmission electron microscopy and Kikuchi electron diffraction. This showed that nucleation appeared to occur via a sub-grain coalescence process that occurred selectively at deformation bands and at deformation band, grain boundary junctions. Nucleation occurred only at grain boundaries and at deformation bands. The condition for continued growth, of enlarged sub-grains of length 2L, along the grain boundary L>2r( _s/ _g) where _s is the sub-boundary energy and _g the grain-boundary energy, was found to be obeyed. The values of the stored energy calculated from the measured sub-grain sizes and misorientations were less than the reported experimental value, indicating that in as-deformed aluminium the dislocation arrays in the sub-boundaries may not have the lowest energy structure assumed in the calculation.     

On the modeling of the static recrystallization considering the initial grain size effects

Modeling of the static recrystallization in deformed copper specimens with different initial grain sizes is carried out based on a previous dislocation–grain size interaction model and a Monte Carlo simulation. From the dislocation–grain size interaction model, the stored energy of the deformed copper is calculated considering the interaction of the dislocations due to the different initial grain sizes. Then, utilizing the stored energy and Monte Carlo simulation the kinetic of recrystallization and recrystallized grain sizes are obtained. The JMAK plots of the modeling results show that, in conditions of 2D modeling and site-saturated nucleation, the Avrami exponent is 2 ± 0.1. The time for 50% recrystallization and recrystallized grain size increase by increasing the initial grain size at a specific strain and are consistent with the experimental data.     

Kinetics of precipitation hardening phase in aluminium alloy AA 6110

Abstract

The solid solution treated aluminium alloy AA 6110 was investigated using a differential scanning calorimetry (DSC) with different heating rates. Kinetic parameters, e.g. the activation energy and the Avrami exponent, were calculated. The peak temperatures of the hardening phase β″ from each heating rate were collected to calculate the activation energy of the aluminium alloy AA 6110 using various mathematical models: the Kissinger, Ozawa and Boswell models. It was found that the activation energies from each model were within the range of 106–114 kJ mol^?1. These activation energies were found to be lesser than those for the bulk diffusion of aluminium, magnesium and silicon atoms in aluminium matrix. The average Avrami exponent, n of 2·36 was calculated using the developed Matusita model and corresponded to a one-dimensional linear growth of fresh nuclei of needle-like β″ in this aluminium alloy AA 6110.     

Effect of zirconium addition on the recrystallization behaviour of a commercial Al-Cu-Mg alloy

It is well known that the second phase particles have an effect on recrystallization and grain growth behaviour of an alloy. Particularly the bimodal distribution of second phase particles has an effect which is opposite in sense where coarse second phase particles (> 1 μm) stimulate nucleation while fine particles exhibit Zener drag. In the literature, the effect of zirconium addition to aluminium alloys has been well documented in order to produce superplasticity by giving ultra fine grain size to the alloy. Addition of zirconium produces Al ₃ Zr particles which pin the grain boundaries during recrystallization and grain growth. In the present work, zirconium was added to a commercial Al-Cu-Mg alloy and by heat treatment Al ₃ Zr particles were precipitated and after forging, the grain size was an order of magnitude lower than the alloy without zirconium. Transmission electron microscopy was employed to characterize the second phase particles, i.e. Al ₃ Zr particles and found to be rod shaped and identified to be cubic ordered L 1 ₂ phase with a lattice parameter of 0.408 nm. Further, it was observed that fine (100 nm) Al ₃ Zr particles promote only continuous recrystallization which is polygonization of subgrains and subgrain growth. It was found that the fine dispersion of Al ₃ Zr particles inhibits both recrystallization and grain growth in the commercial Al-Cu-Mg alloy.     

Effects of solute content on microstructure of nano precipitate-fine grain synergistically reinforced copper alloys

ABSTRACT

Alloying of Fe, Co was reported to tailor microstructure of copper alloys into a nanoprecipitate-fine grain (NPFG) structure, i.e. nano-sized iron-rich precipitates dispersed inside refined grains. Here, we investigate the solute effect of Sn, Zn on NPFG structure in as-cast copper samples. Mechanisms are proposed to account for the solute effect on precipitate and grain features. Solutes restrict coarsening but facilitate undesirable morphology transition from spherical to angular of iron-rich precipitates. Meantime, solutes allow more precipitates to be active in the nucleation of copper and consequently induce finer grains. Minor Sn is added to optimise NPFG structure and leads to an excellent strength–ductility combination in Cu–1.5Fe–0.1Sn (wt-%) alloy. This work provides a solute-alloying strategy to achieve desired mechanical properties in metals.     

Texture mechanism in some fcc-type soft magnetic materials

The authors have studied the mechanism for recrystallization texture in some soft magnetic materials with fcc crystal structure. The alloys used were 77% Ni-14% Fe-5% Cu-4 wt% Mo permalloys. Thin foils selected area electron diffraction (SAD) and X-ray diffraction techniques were employed using a Philips 300 Electron Microscope (EM 300) and an X-ray diffractometer, respectively. Investigations were carried out on deformed, recovered and recrystallized states of the alloys. The various results show that the cold-rolled (deformed) and recovered states of the alloys possess copper-type of rolling texture with {110} 〈112〉 texture as the predominant deformation texture though other minor components such as {112} 〈111〉, {110} 〈001〉 and {123} 〈420〉 textures were detected. No cube texture, {100} 〈001〉 was detected in any of the deformed and recovered materials though the recrystallization texture in these alloys is the cube texture, {100} 〈001〉 which forms over 80% of the annealing texture in these alloys. It is concluded here that the detection of cube texture in the deformed and recovered materials is not a prerequisite for the detection of cube texture in these alloys. The present work is not conclusive about the mechanism for recrystallization texture, but it is proposed here that recrystallization texture, in these alloys is attributed to the growth-oriented mechanism based on the following model. (1) The lattice domains which form the recrystallization texture are present in the cold-rolled matrix. (2) The favoured site for nucleation are the grain boundaries and deformation band boundaries. (3) For the nucleus to be able to grow and form the recrystallization texture it must possess the necessary free energy. (4) Grains must be capable of growth into two or more orientations between which it forms, i.e. the nuclei which form the cube texture should have a [111] pole in common with the matrix in which they grow and a rotation of about 30° around this pole.     

微观组织对电解电容器铝箔比电容的影响

主要探讨了微观组织结构对电解电容器用铝箔比电容的影响。分析表明，高压阳极铝箔需要具有95％以上的立方织构以及一定的晶粒度；软各中低压阳极铝箔需要有75％～85％的立方织构，防止粗大的第二相产生，正品粒要求细小；硬念中低压阳极铝箔需要有高的位错密度和85％以上的(110)织构。硬态负极铝箔要求全属间化合物粒子细小弥散分布在Al基体中，均匀的位错分布和柯氏气团，从而获得均匀的海绵孔腐蚀。     

Non-Uniform Distribution of Energy Density Near a Crack Tip in the Framework of HRR Model

The energy density distribution in the frame work of HRR model (Hutchinson, 1968a; Rice and Rosengren, 1968) is obtained. The analysis indicates that within a sector ahead of a crack, the hydrostatic stresses are very high while the effective stresses are very small, near to the yield stress, so the elastic strain energy density of volume deformation prevails in the forward sector. However, this sector is nearly a "rigid area" in HRR field (Hutchinson, 1968b). Meanwhile, a large amount of plastic dissipation distributes out of the sector, where the plastic dissipation makes up the main part of the J value. The high constraint means that the high elastic volume energy is stored in the local sector, thus the one-parameter fracture criterion based on J is invalid.     

Evaluation of crystallographic changes and plastic strain ratio in Al alloys

Over the past several decades, extensive research endeavours in the field of crystal plasticity (CP) have led to the development of various Taylor-type homogenisation models enabling simulation of texture evolution during plastic deformation. This contribution provides a brief summary on the quality of deformation texture modelling under various boundary conditions. The crystallographic evolutionary patterns are discussed on the basis of grain interaction phenomena incorporated in the CP calculations. The annealing textures are successfully simulated by considering strain heterogeneities in the particle affected zone and by employing orientation selection during both nucleation and growth stages of recrystallisation. It is shown that the Lankford value profiles can be accurately reproduced by CP calculations on condition of reliable grain statistics.

This paper is part of a Themed Issue on Aluminium-based materials: processing, microstructure, properties, and recycling.     

Effect of recrystallization and texture on mechanical properties of extruded AA7003 alloy

The microstructure, texture and mechanical properties of AA7003 extrusion sheets processed with different parameters were investigated. Furthermore, the effects of the microstructure and texture on the mechanical properties were discussed. The grain morphology and the texture were analyzed by using a combination of scanning electron microscopy and electron backscatter diffraction. Moreover, the mechanical properties were measured by tensile tests and the tensile fracture morphology was also analyzed by scanning electron microscopy. The results showed that the maximum recrystallization extent occurred at the extrusion process conditions of T = 450 °C and v = 1 mm/s, and the increase in recrystallization extent had a negative effect on the tensile strength. Moreover, a relatively strong recrystallization cube orientation <100> existed when the extrusion temperature was 470 °C, showing a high tensile strength and elongation. Thus, it can be concluded that the cube texture is beneficial to the tensile strength and elongation in extruded AA7003 alloy.     

Factors affecting dynamic recrystallization of metals and alloys

Abstract

The high-temperature mechanical behaviour of copper, Cu–Al alloys, and nickel has been examined using torsional testing with hollow testpieces in conjunction with microstructural observations on deformed and quenched specimens using both optical and electron microscopy. Dynamic recrystallization occurred in these materials as the restoration process during high-temperature deformation. The factors influencing dynamic recrystallization have been considered, including materials of high stacking fault energy. It was found that the regime of dynamic recrystallization and the transition in flow stress behaviour could be reasonably represented in terms of the Zener–Hollomon parameter. In Cu–Al solid solution alloys, although the addition of the solute aluminium into copper lowered the stacking fault energy, dynamic recrystallization was retarded to higher strains due to the reduced mobility of the grain boundary. By mechanical and microstructural analysis of the behaviour of various single phase metals and alloys during dynamic recrystallization, the factors influencing the behaviour (i.e. stacking fault energy (solute elements), Zener–Hollomon parameter (deformation condition), and strain) can be summarized on a three dimensional schematic.

MST/587