Grain Refinement In Aluminum Alloys Research Articles

Effect of the alloy composition on the grain refinement of aluminum alloys

Abstract Experiments were carried out to evaluate the effect of solute elements on grain refinement in aluminum based hypoeutectic alloys. Grain sizes of the as-cast structures were measured. The measured grain sizes were plotted vs. the undercooling parameter, P , the growth restriction factor, Q , and the solidification interval, Δ T , of the alloys. The results indicated that grain sizes decrease monotonically with increasing Δ T over the whole range of the hypoeutectic compositions whereas the relationships between the grain size and P or Q are “V” type curves.

Grain refinement of aluminum alloys by friction stir processing

Combining friction stir processing (FSP) with rapid cooling, samples with grain sizes of ∼100, 180, 300 and 500 nm have been produced in commercial 7075 Al by controlling the cooling rate. Microstructure characteristics of the processed materials were investigated. The nanocrystalline structures formed in the sample processed with the highest cooling rate consist of high-angle grain boundaries, and are free of dislocation cell structures. High temperature discontinuous dynamic recrystallization is the mechanism responsible for the nanocrystalline creation. Dislocations and recovery structures were observed in the large grains of samples with slower cooling rates. The developed grains are a result of the evolution of the initial nanocrystals formed around pin tool during the FSP.

Mechanisms of grain refinement in aluminum alloys in the process of severe plastic deformation

A study of the mechanisms of grain refinement in the process of severe plastic deformation of two aluminum alloys, i.e., 2219 bearing nanometric particles of Al3Zr and low-alloy Al-3% Cu, is described. The alloys are deformed by the method of equal channel angular pressing at 250°C to a maximum strain degree of about 12. The angles of (sub)grain boundaries in alloy 2219 are determined with the help of transmission electron microscopy by the method of Kikuchi lines. The evolution of the microstructure in alloy Al-3% Cu is studied with the help of grain-boundary maps obtained by the method of electron back-scattered diffraction.

321 圧縮ねじり加工によるアルミニウム合金の組織微細化(OS3-1,OS3 新材料の機能と強度)

321 圧縮ねじり加工によるアルミニウム合金の組織微細化(OS3-1,OS3 新材料の機能と強度)

In situ investigation of the crystallization kinetics and the mechanism of grain refinement in aluminum alloys

The crystallization kinetics during the liquid to solid phase transformation of pure aluminium and various Al–Ti–B alloys is investigated using differential thermal analysis (DTA) and three-dimensional X-ray diffraction (3D XRD). A reduced undercooling required to activate nucleation of aluminum grains is observed, when both solute titanium and TiB 2 particles are present in the liquid. The cooling rate dependence of the onset temperature T o, the crystallization peak temperature T P, and the latent heat Δ H are evaluated and compared for all samples. The DTA curves for slow cooling of an Al–0.3Ti–0.02B (wt.%) alloy illustrate the formation of an aluminide phase (TiAl 3) upon solidification. A comparison of the DTA curves during slow cooling of the hypoperitectic Al–0.1Ti–0.1TiB 2 (wt.%) and the hyperperitectic Al–0.3Ti–0.02B (wt.%) alloys seem to exhibit a kinetic similarity at the onset of the solidification. In situ 3D XRD measurements clearly exhibit the formation of a metastable TiAl 3 phase prior to solidification of both alloys. This explains the mechanism of grain refinement in the presence of solute titanium and TiB 2 particles in the grain refined aluminum alloys. The influence of titanium diffusion, latent heat, and cooling rate on the growth behaviour of individual aluminium grains during the phase transformation is further quantified.

Mechanisms of Grain Refinement in Aluminum Alloys during Severe Plastic Deformation

The mechanisms of grain refinement during severe plastic deformation have been studied, by comparing the microstructure evolution in an AA2219 aluminium alloy, containing Al3Zr nanoscale particles, with that in a dilute Al-3%Cu alloy deformed identically by equalchannel angular extrusion (ECAE) at 250oC to a maximum strain of ~12. Transmission electron microscopy (TEM) was used on the AA2219 alloy to reveal the misorientations of deformationinduced boundaries. Microstructural evolution in the Al-3%Cu alloy was studied by electron-back scattering diffraction (EBSD) orientation mapping. It was shown that the mechanism of grain refinement in the AA2219 alloy is continuous dynamic recrystallization (CDRX) consisting of two main elementary processes. In the initial stages of plastic deformation, the formation of threedimensional arrays of low-angle boundaries (LABs) takes place. Further strain results in increasing misorientation of these boundaries providing their gradual transformation into high-angle boundaries (HABs). A fully recrystallized structure with an average grain size of ~0.9 µm is evolved after a total strain of ~12. In the dilute Al-Cu alloy the evolution of ultrafine grains with an average size of ~6 µm is attributed to the formation of deformation bands outlined by HABs and extended medium to high-angle boundaries at moderate strains. The subdivision of these deformation bands into fine grains rarely occurs through the mechanism of geometric recrystallization (GRX). In this alloy the main contribution in the grain refinement gives CDRX occurring within fibrous structural features. At e~12, a partially recrystallized structure is formed in the Al-3%Cu alloy.

Asymmetric Rolling as Means of Texture and Ridging Control and Grain Refinement of Aluminum Alloy and Steel Sheets

Asymmetric rolling, in which the circumferential velocities of the upper and lower rolls are different, can give rise to intense plastic shear strains and in turn shear deformation textures through the sheet thickness. The ideal shear deformation texture of fcc metals can be approximated by the <111> // ND and {001}<110> orientations, among which the former improves the deep drawability. The ideal shear deformation texture for bcc metals can be approximated by the Goss {110}<001> and {112}<111> orientations, among which the former improves the magnetic permeability along the <100> directions and is the prime orientation in grain oriented silicon steels. The intense shear strains can result in the grain refinement and hence improve mechanical properties. Steel sheets, especially ferritic stainless steel sheets, and aluminum alloy sheets may exhibit an undesirable surface roughening known as ridging or roping, when elongated along RD and TD, respectively. The ridging or roping is caused by differently oriented colonies, which are resulted from the <100> oriented columnar structure in ingots or billets, especially for ferritic stainless steels, that is not easily destroyed by the conventional rolling. The breakdown of columnar structure and the grain refinement can be achieved by asymmetric rolling, resulting in a decrease in the ridging problem.

Grain Refinement of Aluminium Alloys by Inoculation

AbstractA review is given of the studies of aluminium inoculation undertaken within the EU Network “Microstructural Engineering by Solidification Processing” (MEBSP). A wide range of studies of industrial practice of grain refining and of the fundamental mechanisms of nucleation and growth have contributed to improved understanding. Particular advances have been made in understanding the relative performance of different grain refiners.

アルミニウム合金の結晶粒微細化へ及ぼすひずみ負荷様式の影響

アルミニウム合金の結晶粒微細化へ及ぼすひずみ負荷様式の影響

Effects and mechanisms of grain refinement in aluminium alloys

Grain refinement plays a crucial role in improving characteristics and properties of cast and wrought aluminium alloys. Generally Al-Ti and Al-Ti-B master alloys are added to the aluminium alloys to grain refine the solidified product. The mechanism of grain refinement is of considerable controversy in the scientific literature. The nucleant effects i.e. which particle and its characteristics nucleate α-Al, has been the subject of intensive research. Lately the solute effect i.e. the effect of dissolved titanium on grain refinement, has come into forefront of grain refinement research. The present paper attempts to review the literature on the nucleant effects and solute effects on grain refinement and addresses the importance of dissolved titanium in promoting nucleation of α-Al on nucleant particles.

Influence of silicon and magnesium on grain refinement in aluminium alloys

Grain refinement in Al–Si alloys with silicon contents in the range of 0·2–30 wt-% has been studied in detail with conventional as well as higher level additions of a Al–5Ti–1B master alloy. A poisoning effect was observed with Al–Si alloys containing ≥7 wt-%Si and the extent of poisoning increased with an increase in the silicon content. Silicon improves the grain refining behaviour of aluminium when added in small quantities (0·2%). Magnesium can counteract the poisoning effect of silicon. The optimum level of magnesium required to overcome the poisoning effect depends on the silicon content of the alloy. Higher level additions of a grain refiner could overcome the poisoning effect of silicon and the level required to achieve good grain refinement is a function of the silicon and magnesium contents of the alloy. The present paper also reports the influence of degasser and melt temperature on the grain refining response of Al–Si alloys.

Grain refinement of aluminum alloys: Part I. the nucleant and solute paradigms—a review of the literature

Despite the extensive literature on grain refinement, there is not a consensus on the mechanism of grain refinement in aluminum alloys. Recently, there has been a shift in understanding of the grain-refinement paradigm from purely being concerned with the nucleation event, called here the “nucleant paradigm,” to also being concerned with the effect of solute elements, or, the “solute paradigm,” on the final grain structure. This article is divided into two parts. In Part I, the literature underpinning both paradigms is explained, and the validity of the paradigm shift toward the solute paradigm as a more complete understanding of grain refinement is presented. Part II experimentally confirms the validity of the solute paradigm and details a mechanism which explains the need for both effective nucleants and a solute of a good segregating power in order to obtain grain refinement.

Modelling of Grain Refinement in Aluminium Alloys

AbstractCommercial grain refiners for aluminium solidification are so potent that the barrier forgrain initiation is that for free growth rather than for nucleation itself. In this case quantitative prediction of grain size is possible. For small melt volumes a successful isothermal-melt model is presented. This is extended to directional solidification in a temperature gradient using cellular-automaton modelling of grain growth with finite-element heat-flow calculations.

極低温・異方向圧延により加工した３００４および５０８３アルミニウム合金の蓄積エネルギーと再結晶

Grain refinement of aluminum alloys can be achieved by introducing a large amount of lattice distortions during an intense plastic deformation. In order to introduce high plastic strain to 3004 and 5083 aluminum alloys and to restrain a dynamic recovery, a two-directional rolling method at cryogenic temperature was applied. Superiority of the two-directional rolling method was verified by a stored energy obtained from differential scanning calorimetry (DSC) analysis, by a microstructure and by a work hardening. The stored energy and work hardening given by the two-directional rolling at cryogenic temperature to 50% reduction of area were larger than those given by the other types of rolling with same reduction such as two-directional rolling at room temperature, one-directional rolling at cryogenic temperature and one-directional rolling at room temperature. A recrystallized grain size at peak temperature of remarkable exothermal reaction was smallest in the two-directional rolling at cryogenic temperature compared with in the other rolling conditions. The recrystallized grain size at the peak temperature of the exothermal reaction was decreased with increasing the stored energy. The work hardening on ST–LT cross-sectional plane of these alloys strained by the two-directional rolling at cryogenic temperature was distributed more uniformly compared with that of these alloys strained by the other rolling.

Effect of gravity level on grain refinement in aluminum alloys

Effect of gravity level on grain refinement in aluminum alloys

Effect of gravity level on grain Refinement in Aluminum Alloys

Effect of gravity level on grain Refinement in Aluminum Alloys

Grain Refinement in Aluminum Alloys by Rapid Solidification

Grain Refinement in Aluminum Alloys by Rapid Solidification

Thermodynamic consideration of grain refinement of aluminum alloys by titanium and carbon

Thermodynamic consideration of grain refinement of aluminum alloys by titanium and carbon

Characterization of submicron particles in Al5Ti1B grain refining master alloys

Al5%Ti1%B master alloys are frequently used in the grain refinement of aluminium alloys to induce heterogeneous nucleation during solidification and to promote an equiaxed grain structure. Boride particles are often observed in these alloys and could act as nucleation sites. However there are many more particles than nucleated grains in the samples and hence the precise role of the borides and other particles is not clear. We have therefore been undertaking a systematic TEM study of submicron particles extracted from master alloys using carbon extraction replication of fractured samples, with a view to investigating the nucleation mechanisms.Many of the particles analysed adopted a well defined hexagonal prism morphology (Fig.1) and varied in size from 5μm to 100 nm across the hexagonal face. A combination of EDX and EELS analysis plus electron diffraction was used to identify isolated particles as TiB2 containing little if any aluminium or potassium. These other elements are often detected in agglomerations of particles.

Application of a thermomechanical process for the grain refinement of aluminum alloy 7475

A thermomechanical process, concluding with warm rolling, was applied to aluminum alloy 7475 to assess the degree of grain refinement attainable with it. The processing method has been shown to result in a grain size of 2–5 μm in AlMg alloys, with superplastic ductility obtained at lower temperatures (573 K (300 °C)) and higher strain rates ((2–5) × 10 −3 s −1) than generally reported for wrought aluminum alloys. This was attributed to continuous recrystallization of an initially severely worked microstructure; when applied to aluminum alloy 7475, it was necessary to include precipitation treatments prior to the warm working. It was found that a dispersion of 0.2 μm precipitate particles resulted in sufficiently fine, continuously recrystallized grains to give enhanced ductility in aluminum alloy 7475 at warm temperatures. Coarser precipitates resulted in discontinuous recrystallization and a coarser grain size with concomitant less warm temperature ductility, while finer precipitates were not as effective in retarding boundary migration and producing microstructure refinement.