Formation Of Guinier-Preston Zones Research Articles

Tweed microstructure of copper-beryllium

The tweed microstructure in aged copper-beryllium alloys has usually been associated with the formation of disk-shaped Guinier-Preston zones on {100} planes, and the coherency strain fields surrounding them. However, tweed contrast and/or diffraction effects have been observed by electron microscopy in as-quenched material and in samples subjected to reversion treatment in which the GP zones redissolve. A Cu-1 wt. % Be alloy has been examined by transmission electron microscopy and diffraction to test the hypothesis that GP zones are not responsible for the tweed contrast.

Phonon dispersion relation of aluminum-copper with the Guinier-Preston zone formation

The phonon dispersion relation of ζ00 T branch of Al-1.8 at.% Cu has been measured by means of neutron inelastic scattering. A single crystal specimen aged at room temperature between 17 and 72 hr. after quenching from 550°C shows a strong resonance mode at the energy of about 2.5 THz. This resonance mode cannot be explained by the calculation based on the simple mass-defect model, and may be attributed to the formation of the Guinier- Preston zone.

Comments on ?the influence of Mg contents on the formation and reversion of Guinier-Preston zones in Al-4.5at% Zn-xMg alloys

Comments on ?the influence of Mg contents on the formation and reversion of Guinier-Preston zones in Al-4.5at% Zn-xMg alloys

Resistivity maximum during Guinier-Preston zone formation in an Al-4 wt% Cu alloy

Abstract In order to examine the scattering of conduction electrons from Guinier-Preston (GP) zones, the electrical resistivity (ρ) and the Hall coefficient have been measured. Quantitative information on the microstructure of aged alloys was obtained from small-angle X-ray scattering measurements. The resistivity behaves anomalously during isothermal ageing; it increases to a maximum, then decreases and reaches a value corresponding to the steady state of the growth of GP zones. A further decrease occurs when the θ˝ phase begins to precipitate. During these changes, the zone size increases, and reaches a constant value which is slightly larger at higher ageing temperatures. The change in volume fraction (V f) of precipitated zones is quite similar to the change in zone size. It was found that the function (ρ - ρAsQ)/V f depends on the zone size. The origin of the resistivity maximum is discussed, based on the theory proposed by Hillel, Edwards and Wilkes.

A neutron scattering investigation of the early stages of guinier-preston zone formation in AlZnMg(Cu)-alloys

A diffuse neutron scattering investigation of the early stages of the Guinier-Preston zone formation in AlZnMg(Cu)-alloys has been made. All samples show at smaller wavevectors (<1 Å −1) elastic diffuse intensity which can be described by two Guinier radii. The smaller radius does not change with annealing time and may indicate the presence of small ‘nuclei’, unaffected by the further decomposition. The larger radius, however, shows a considerable time dependence and characterizes the size of the Guinier-Preston zones. For larger annealing times normal growth was found, but for times just after quench a decrease of the radius was observed. This decrease may be explained in the following way: just after quench greater but dilute Guinier-Preston zones form, which with time become smaller and denser. Only after this initial compactification the normal growth starts.

Positron experiments on the formation and growth of Guinier-Preston zones in AlZn alloys

Positron lifetime and annihilation lineshape measurements have been performed to study the behaviour of vacancies during GP zone formation and growth in various Al-Zn alloys quenched to 200K. The results suggest that vacancies in these alloys are surrounded by Zn atoms. Vacancy recovery is found only above 220K when GP zones already exist in the lattice. Above room temperature the well-developed zones are free of vacancy-type defects.

The influence of Mg content on the formation and reversion of Guinier-Preston zones in Al-4.5 at % Zn-x Mg alloys

The influence of Mg concentrations on the dissolution of Guinier-Preston (GP) zones formed at room temperature (RT) and on the formation of more stable phases has been investigated during continuous heating of Al-4.5 at % Zn-xMg alloys. The Mg content was varied from 0.05 to 3 at %. After different aging periods at RT, calorimetric investigations were carried out at heating rates of 40 and 80° C min−1. In the case of alloys with a lower Mg content (x ⩽ 0.5 at %) only the dissolution of GP zones could be observed during the heating, whereas in the case of alloys with a higher Mg content the formation of theη′-phase started before the total dissolution of GP zones and at higher temperatures the formation of theη-phase also took place. These phases were identified by transmission electron microscopy. The heat-of-solution of GP zones shows saturation as a function of RT aging time. The time needed for the saturation increased monotonously with increasing Mg content. The reversion of zones was followed byin situ X-ray small angle scattering measurements. The change of the total scattered intensity was measured during continuous heating at a rate of 40° C min−1. These investigations have confirmed the results of the calorimetric measurements which indicate that the total dissolution of zones takes place only in the case of the alloys with a Mg content lower than 0.5 at %. In the case of alloys with a Zn concentration of 4.5 at % studied here, 1 at % Mg is sufficient to initiate the formation of more stable phases during the reversion of zones.

The influence of Mg content on the formation and reversion of Guinier-Preston zones in Al-4.5 at % Zn-x Mg alloys

The influence of Mg content on the formation and reversion of Guinier-Preston zones in Al-4.5 at % Zn-x Mg alloys

Precipitation in Al-Li-Cu Alloys

Al-Li-Cu alloys combine high specific strength and high specific modulus and are potential candidates for aircraft structural applications. As part of an effort to optimize Al-Li-Cu alloys for specific applications, precipitation in these alloys was studied for a range of compositions, and the mechanical behavior was correlated with the microstructures.Alloys with nominal compositions of Al-4Cu-2Li-0.2Zr, Al-2.5Cu-2.5Li-0.2Zr, and Al-l.5Cu-2.5Li-0.5Mn were argon-atomized into powder at solidification rates ≈ 103°C/s. Powders were consolidated into bar stock by vacuum pressing and extruding at 400°C. Alloy specimens were solution annealed at 530°C and aged at temperatures up to 250°C, and the resultant precipitation was studied by transmission electron microscopy (TEM).The low-temperature (≲100°C) precipitation behavior of the Al-4Cu-2Li-0.2Zr alloy is a combination of the separate precipitation behaviors of Al-Cu and Al-Li alloys. The age-hardening behavior at these temperatures is characteristic of Guinier-Preston (GP) zone formation, with additional strengthening resulting from the coherent precipitation of δ’ (Al3Li, Ll2 structure), the presence of which is revealed by the selected-area diffraction pattern (SADP) shown in Figure la.

Small-angle neutron scattering from Al-Zn and AI-Zn-Mg alloys during Guinier-Preston zone formation

Small-angle neutron scattering from A1-6.8 at % Zn and Al-6.8 at % Zn-0.1 at % Mg alloys during Guinier-Preston zone formation have been measured at KUR (Kyoto University Reactor). The samples were quenched from 300 °C into brine at -20 °C and kept at 77 K. They were aged at 40 °C for various periods ranging from 0 up to 1000 minutes each with subsequent neutron measurement at 77 K. The observed temporal evolution of the cross section can be interpreted qualitatively in terms of Saito's formula which consists of two distinct parts due to the incoherent anomalous fluctuation and to the coherent ordered structure of the concentration.

Small-angle x-ray scattering study of precipitation in aluminum-zinc implanted alloys

X-ray small-angle scattering is an appropriate tool for the study of inhomogeneities in alloys, as the accessible range of scattering vectors yields the required spatial resolution. It was often used in the past for pre-precipitation studies, i.e. Guinier-Preston zone formation, in supersaturated AlZn solid solutions obtained after quenching. However, it has not yet been used for implanted alloys because of insufficient depth penetration and consequently volume fraction of scattered particles. For this reason a specific camera has been built, employing a positron-sensitive proportional counter which registers the scattering pattern by accumulation and allows measurements of very weak intensities. A comparison will be made in this study between a sample with approximately 7 at.% Zn implanted into an aluminum foil and the well-studied Al-6.8% Zn alloy.

ChemInform Abstract: STUDY OF THE ELASTIC BEHAVIOR OF AN ALUMINUM‐ZINC ALLOY DURING FORMATION OF GUINIER‐PRESTON ZONES

Chemischer InformationsdienstVolume 12, Issue 11 Physical Inorganic Chemistry ChemInform Abstract: STUDY OF THE ELASTIC BEHAVIOR OF AN ALUMINUM-ZINC ALLOY DURING FORMATION OF GUINIER-PRESTON ZONES W. SIEBKE, W. SIEBKESearch for more papers by this authorC. FRIEDRICH, C. FRIEDRICHSearch for more papers by this author W. SIEBKE, W. SIEBKESearch for more papers by this authorC. FRIEDRICH, C. FRIEDRICHSearch for more papers by this author First published: March 17, 1981 https://doi.org/10.1002/chin.198111003AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume12, Issue11March 17, 1981 RelatedInformation

Calculation of the binding energies of complexes formed by magnesium and zinc impurity atoms with vacancies in dilute aluminum alloys

Expressions are obtained for calculating the binding energy of an arbitrary complex formed from impurity atoms and vacancies. Calculations are made for various complexes formed from magnesium and zinc impurity atoms and vacancies in aluminum. The results obtained are used to study the role of vacancies in the formation of Guinier-Preston zones. The need to allow for the lattice relaxation is demonstrated.

The Formation of Guinier-Preston Zones in the AI-4.8 wt.% Zn-1.2 wt.% Mg Alloy Studied by X-Ray Small Angle Scattering

The Formation of Guinier-Preston Zones in the AI-4.8 wt.% Zn-1.2 wt.% Mg Alloy Studied by X-Ray Small Angle Scattering

Durcissement observe dans un alliage Al-Zn à 6,8 % at. au cours d'une decomposition spinodale

X-ray small-angle scattering is an appropriate tool for the study of inhomogeneities in alloys, as the accessible range of scattering vectors yields the required spatial resolution. It was often used in the past for pre-precipitation studies, i.e. Guinier-Preston zone formation, in supersaturated AlZn solid solutions obtained after quenching. However, it has not yet been used for implanted alloys because of insufficient depth penetration and consequently volume fraction of scattered particles. For this reason a specific camera has been built, employing a positron-sensitive proportional counter which registers the scattering pattern by accumulation and allows measurements of very weak intensities.A comparison will be made in this study between a sample with approximately 7 at.% Zn implanted into an aluminum foil and the well-studied Al-6.8% Zn alloy.

Etude par microscopie electronique de la decomposition de l'alliage Al-6,8 at.% Zn

The decomposition of an Al-6.8% Zn alloy was studied using electron microscopy at different aging temperatures within the range of formation of Guinier-Preston zones. The increase in number (~10 15/cm 3) and in size of the zones that was observed during aging at 133°C indicates that the appearance of the zones is governed by a nucleation and growth mechanism. Spinodal decomposition is the interpretation given for the markedly different development at both 20 and 80°C of the decomposition structure observed during the first stages by a slowing down of the kinetics as a result of quenching in steps, and by having a constant density (~5 × 10 18/cm 3) of clusters which become rich in Zn and develop finally into G.P. zones. At 110°C the morphology resembles that observed at 133°C. The advanced stages of the decomposition confirm the development of the G.P. zones into α′ R precipitates with a rhombohedral structure: this transformation which occurs progressively at 20°C is more sudden at 133°C.

A comment on the electrical resistivity during G.P. zone formation

Abstract Two recent theories describing the behaviour of the electrical resistivity during Guinier-Preston zone formation of Rossiter and Wells (RW) and Hillel, Edwards and Wilkes (HEW) are compared. It is shown that the HEW theory is a simplification of the RW theory and lacks important terms due to electron scattering at the zone boundaries.

Variations of the elastic and anelastic properties of aluminium-magnesium alloys with the evolution of Guinier-Preston zones

Ultrasonic velocities and attenuation have been measured at 6 and 15 MHz during isothermal ageing processes at 20°C for Al-Mg supersaturated solid solutions of three concentrations 12, 13.5 and 16 at. % magnesium. The velocities and the elastic moduli increase with ageing time, whilst the attenuation decreases. These effects are due to the formation and growth of Guinier-Preston zones. The effects of grain scattering and of internal friction to attenuation have been separated. Internal friction causes a decrease on attenuation in the first phases of development of GP zones, whereas grain scattering involves an increase in later stages.

Al-Ag合金における伝導電子の散乱におよぼすG.P.ゾーンのサイズおよび内部構造の影響

It is well known that during a preprecipitation process in which the formation of Guinier-Preston zones takes place, an increase of resistivity at its early stage, followed by a decrease, occurs in a number of age-hardenable aluminium-base alloys. Recently we have experimentally determined the contribution of one G.P. zone to the electrical resistivity and discussed the influence of size and shape of G.P. zones on the scattering power in Al-Zn alloys. It has been shown that the scattering power of a G.P. zone increases with its size.The objects of the present paper are to investigate in detail the influence of size and inner structure of G.P. zone on the scattering power for Al-Ag alloys in which two kinds of G.P. zones are known to form at each aging temperature and to compare with the scattering power of G.P. zones in Al-Zn alloys. The electrical resistivity and X-ray small-angle scattering measurements have been performed for several Al-Ag alloys aged at 140 and 190°C.It is shown that the scattering power of a G.P. zone increases with its size, though the size dependence is different for each aging temperature. This behavior of the scattering power is explained in terms of the difference in the inner structure of G.P. zones in Al-Ag alloys.

Theory of the resistivity and Hall effect in alloys during Guinier-Preston zone formation

Abstract The theory of the resistivity maximum, based on Bragg scattering of electrons from Guinier-Preston zones, is described and is used to construct semi-phenomenological formulae for the resistivity appropriate to various types of alloy configuration. When the parameters are determined from transport calculations the formulae will be useful in analysing the state of an alloy during ageing. It is shown, for example, that the size of cluster associated with peak resistivity varies with solute concentration and ageing temperature, but this is much less so for spherical zones than for flat zones. The theory is also able to reproduce the behaviour of the Hall coefficient in Al-Zn, which also peaks during ageing. It is argued that other zone-forming alloys may exhibit a maximum, a minimum or neither.