Origins of hardening in aged AlGuMg(Ag) alloys

Ringer, Simon P.; Sakurai, T.; Polmear, I. J.

doi:10.1016/s1359-6454(97)00039-6

Cited by 318 publications

(179 citation statements)

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“…Therefore when quenching large industrial components, rapid hardening should already take place during quenching and will vary across the cross section of the component depending on the local cooling conditions. The rapid hardening during quench increases the yield strength by cluster strengthening [2] and influences the residual stress formation [13]. Therefore, the Cu-Mg cluster formation needs to be taken into account in the simulation of residual stresses by precipitation modeling [11,12].…”

Section: Introductionmentioning

confidence: 99%

“…The first stage is defined by a fast initial increase in strength, which is known as rapid hardening. It was shown by 3D atom probe tomography (APT) and small-angle X-ray scattering (SAXS) experiments that the rapid hardening is associated with the formation of Cu-Mg clusters [1][2][3][4]. The second rise to peak hardness is generally ascribed to the formation of the equilibrium S phase (Al 2 CuMg) [4,5].…”

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confidence: 99%

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Early cluster formation during rapid cooling of an Al–Cu–Mg alloy: In situ small-angle X-ray scattering

et al. 2015

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a b s t r a c tThe formation of Cu-Mg clusters in an Al-Cu-Mg aluminum alloy is observed by small-angle X-ray scattering during cooling. Cooling rates are choosen to mimic the different conditions obtained at the surface and in the center of large forgings. Clusters of 0.45 nm start to form at 250°C. Their volume fraction depends strongly on the cooling rate and the amount of excess vacancies. The difference in cluster kinetics explains the difference in rapid hardening across large forgings.Ó 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.Age-hardenable Al-Cu-Mg alloys are widely used for aerospace and engineering applications owing to their high specific strength and good corrosion resistance. Their age hardening response is characterized by two distinct stages. The first stage is defined by a fast initial increase in strength, which is known as rapid hardening. It was shown by 3D atom probe tomography (APT) and small-angle X-ray scattering (SAXS) experiments that the rapid hardening is associated with the formation of Cu-Mg clusters [1][2][3][4]. The second rise to peak hardness is generally ascribed to the formation of the equilibrium S phase (Al 2 CuMg) [4,5].For industrial applications, the Al-Cu-Mg alloys are commonly processed as large components such as forgings or plates. The mechanical properties are tailored by the age-hardening treatment, which also involves a quenching step. Thermal gradients decrease from the surface to the center and give rise to residual stresses (RS) [6]. The magnitude of the as-quenched RS can be very high and even exceed the as-quenched strength of the materials [6,7]. In the case of Al-Zn-Mg-Cu alloys, the high as-quenched RS are caused by the formation of fine hardening precipitates that form during quenching of large components and thereby increase the yield strength of the material [8,9].In order to predict the RS formation in industrial components during quench, the changes of the nanostructure during cooling conditions close to industrial practice needs to be characterized as they highly impact the yield strength and thus the internal stress generation. Further, the influence of excess vacancies on precipitation during cooling needs to be explored. This can be done by adapting the cooling rates at high temperature, which influence the excess vacancy concentration due to annihilation on defects.SAXS is a useful tool to monitor precipitation phenomena during fast time and temperature changes given that a sufficiently high electron density contrast between the precipitate and matrix exists [4,8,10]. SAXS provides the means to collect information on the size and volume fraction of the precipitates that can then be directly compared to predictions of thermodynamic-based precipitation models [11,12]. These models can be coupled with macroscopic finite-element RS simulations to better predict the residual stress formation during the processing of industrial components [9,13] as part of through-process modeling.This work investigates the Cu-Mg cluster ...

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Section: Introductionmentioning

confidence: 99%

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confidence: 99%

Early cluster formation during rapid cooling of an Al–Cu–Mg alloy: In situ small-angle X-ray scattering

et al. 2015

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“…This stage accounts for approximately 60% of the total hardness increase during ageing [26]. During this rapid hardening no distinct precipitate can be detected by conventional TEM but DSC experiments clearly show a dissolution effect evidencing that a metastable pre-precipitate has formed [27]. Evidence for the existence of the GPB zones, with a structure distinct from the random structure in co-clusters, is limited [23].…”

Section: Sssmentioning

confidence: 97%

VPPA welds of Al-2024 alloys: Analysis and modelling of local microstructure and strength

Wang

Lefebvre

Yan

et al. 2006

Materials Science and Engineering: A

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The microstructural features of variable polarity plasma arc welded Al-Cu-Mg 2024-T351 with 2319 filler have been studied by TEM, SEM and DSC. Fusion zone, partial melting zone, resolutionising zone, overageing (for S phase), peak ageing (for S phase) and under ageing zones (for S phase) have been identified. The Ω phase has been observed between re-solutionising zone and peak ageing zone. The hardness profile contains two peaks. The microstructure development, and resulting hardness and yield strength profiles are modelled using a model which combines primary precipitation, resolution, partial/full melting and resolidification (Scheil type) and reprecipitation, in a two precipitate -two mechanism approach. Hardness profiles and microstructures are accurately predicted. The hardness peak in the re-solutionising zone is due to re-solutionising and subsequent Cu-Mg co-cluster formation; and the second hardness peak is caused by S phase strengthening.

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“…Therefore, the hardening during the initial 20 h is considered to result primarily from the formation of copper-enriched clusters. The decrease in the lattice parameter after 20 h is considered to have resulted by the formation of magnesium-containing clusters [23], which depletes the magnesium from the matrix, causing the lattice parameter to decrease at a rate of -0.0044 Å/at.% Mg [22].…”

Section: Natural Agingmentioning

confidence: 99%