Tomographic Atom Probe Study of Age Hardening Precipitation in Industrial AlZnMgCu (7050) Alloy

Bigot, A.; Danoix, F.; Auger, Pierre; Blavette, D.; Reeves, Andrew L.

doi:10.4028/www.scientific.net/msf.217-222.695

Cited by 39 publications

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“…We will assume coarsening effectively starts after attaining peak strength, and hence we will choose r o = 2nm and t o = 2h. Our TEM work (see previous section) indicates that after 16h ageing at 172°C precipitate radius has increased to about 5 nm, and this finding is consistent with APFIM work on similar alloys [42]. From this the coarsening rate, K, is determined as 3.9 nm 3 /h.…”

Section: S S 20μmsupporting

confidence: 77%

“…In addition, we will approximate the precipitation by assuming that the precipitation in the grain is exclusively η′ phase. Some controversy exists concerning the composition of the η′ phase, with atom-probe data suggesting a Zn:Mg ratio of about 1.2-1.5 with very low Cu content (Cu:Zn=0.1) [42,43,44], and small angle X-ray scattering (SAXS) a suggesting a much higher Zn content [44], closer to the Zn:Mg ratio of 2.5 in the suggested structure of η′ phase based on an analysis of selected area diffraction data [45]. We will assume that the Zn:Mg ratio can be approximated to equal 2, and that in good approximation η′ does not contain Cu.…”

Section: Precipitation and Coarseningmentioning

confidence: 99%

“…The size of precipitates in our alloys was estimated from the present TEM data and other data appearing in the literature. This assessment indicates that at the peak-aged condition, which a separate assessment for our alloys showed to correspond to about 2 h ageing at 172°C, the precipitate radius is about 2 nm [42,54]. We will assume coarsening effectively starts after attaining peak strength, and hence we will choose r o = 2nm and t o = 2h.…”

Section: S S 20μmmentioning

confidence: 99%

See 2 more Smart Citations

A model for the electrical conductivity of peak-aged and overaged Al-Zn-Mg-Cu alloys

Starink

2003

Metall Mater Trans A

113

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A physically-based model for the electrical conductivity of peak aged and overaged Al-Zn-Mg-Cu (7xxx series) alloys is presented. The model includes calculations of the η and the S phase solvus (using a regular solution model), taking account of the capillary effect and η coarsening. It takes account of the conductivity of grains (incorporating dissolved alloying elements, undissolved particles and precipitates) and solute depleted areas at the grain boundaries. Data from optical microscopy, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) along with energy dispersive X-ray spectrometry (EDS), and transmission electron microscopy (TEM) are consistent with the model and its predictions. The model has been successfully used to fit and predict the conductivity data of a set of 7xxx alloys including both Zr containing alloys and Cr containing alloys under various ageing conditions, achieving an accuracy of about 1% in predicting unseen conductivity data from this set of alloys.

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Section: S S 20μmsupporting

confidence: 77%

Section: Precipitation and Coarseningmentioning

confidence: 99%

Section: S S 20μmmentioning

confidence: 99%

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A model for the electrical conductivity of peak-aged and overaged Al-Zn-Mg-Cu alloys

Starink

2003

Metall Mater Trans A

113

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“…The overall chemical composition of the alloy measured by the three-dimensional atom probe (93.89 at.% Al, 2.67 at.% Zn, 0.72 at.% Cu and 2.62 at.% Mg) is consistent with the nominal composition of the alloy listed in Table 1. The mean chemical composition of the matrix was measured to be 96.0 š 0.3 at.% Al, 1.5 š 0.2 at.% Zn, 0.7 š 0.02 at.% Cu and 1.8 š 0.2 at.% Mg. Based on the selected volume analysis of five precipitates chosen at random, the mean chemical composition was measured to be 67 š 5 at.% Al, 18 š 3 at.% 12 It should be noted that the presence of trajectory aberrations and local magnification effects may cause the Al concentration in small precipitates to be overestimated. 13 However, the atomic density within the three-dimensional atom probe reconstruction does not vary greatly between precipitates and matrix.…”

Section: Resultsmentioning

confidence: 99%

Characterization of precipitates in an aged 7xxx series Al alloy

Sha

Cerezo

2004

Surface & Interface Analysis

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Precipitates in a 7050 Al alloy under two-step ageing treatments were characterized using an energycompensated optical position-sensitive atom probe and transmission electron microscopy. Selected-area diffraction analyses indicated that the early-stage precipitates present after a stabilization ageing treatment at 121• C for 4 h have a crystallographic structure similar to h , but probably rich with defects. After T6 treatment ageing at 121• C for 24 h followed by 12 h at 154• C, h and h coexist within the Al matrix. Energy-compensated optical position-sensitive atom probe analysis was used to measure the partitioning of Zn, Mg and Cu to the precipitates. Early-stage precipitates in the alloy after stabilization treatment have a Zn/Mg ratio of ∼1.3 and a (Zn + Cu)/Mg ratio of 1.4. The T6-aged alloy contained h precipitates with an Zn/Mg ratio of ∼1.2 and a (Zn + Cu)/Mg ratio of 1.3 coexisting with h precipitates with a Zn/Mg ratio of ∼0.7 and a (Zn + Cu)/Mg ratio of ∼1.

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“…[14,17] Hydrogen fugacities on bare aluminum are high, and near-surface dissolved atomic r tip ϭ d n K 2 (1 Ϫ v 2 ) 2E flow [5] hydrogen concentrations can be in excess of ϳ20,000 wt ppm, as shown by nuclear-reaction analysis of AA 7050 crack wakes produced by HEAC when exposed to 90 pct Of course, these theoretical predictions must be used with boundary region, and in the precipitates. [30,[33][34][35][36][37] However,…”

Section: Introductionmentioning

confidence: 99%

The effects of test temperature, temper, and alloyed copper on the hydrogen-controlled crack growth rate of an Al-Zn-Mg-(Cu) alloy

Young

Scully

2002

Metall Mater Trans A

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The hydrogen embrittlement controlled stage I1 crack growth rate of AA 7050 (6.09 wt.% Zn, 2.14 wt.% Mg, 2.19 wt.% Cu) was investigated as a function of temper arid alloyed copper level in a humid air environment at various temperatures. Three tempers representing the underaged, peak aged, and overaged conditions were tested in 90% relative humidity (RH) air at temperatures between 25 and 90 "C. At all test temperatures, an increased degree of aging @om underaged to overaged) produced slower stage II crack growth rates. The stage n crack growth rate of each alIoy and temper displayed Arrhenius-type temperature dependence with activation energies between 58 and 99 kJ/mol. For both the normal copper and low copper alloys, the fiacture path was predominately intergranular at all test temperatures (25-90 "C) in each temper investigated.Comparison of the stage II crack growth rates for normal (2.19 wt.%) and low (0.06 wt.%) copper alloys in the peak aged and overaged tempers showed the beneficial effixt of copper additions on stage II crack growth rate in humid air. In the 2.19 wt.% copper alloy, the significant decrease (-10 times at 25 "C) in stage I1 crack growth rate upon overaging is attributed to an increase in the apparent activation energy for crack growth. Ir: the 0.06 wt.% copper alloy, overaging did not increase the activation energy for crack growth but did lower the pre-exponential factor, vo, resulting in a modest (-2.5 times at 25 "C) decrease in crack growth rate. These resuits indicate that alloyed copper and thermal aging affect the kinetic factors that govern stage II crack growth rate. Overaged, copper bearing alloys are not intrinsicaIly immune to hydrogen environment assisted cracking but are more resistant due to an increased apparent activation energy for stage IT crack growth. BACKGROUND

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Tomographic Atom Probe Study of Age Hardening Precipitation in Industrial AlZnMgCu (7050) Alloy

Cited by 39 publications

References 0 publications

A model for the electrical conductivity of peak-aged and overaged Al-Zn-Mg-Cu alloys

A model for the electrical conductivity of peak-aged and overaged Al-Zn-Mg-Cu alloys

Characterization of precipitates in an aged 7xxx series Al alloy

The effects of test temperature, temper, and alloyed copper on the hydrogen-controlled crack growth rate of an Al-Zn-Mg-(Cu) alloy

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