Precipitation kinetics of GP zones, metastable η′ phase and equilibrium η phase in Al−5.46wt.%Zn−1.67wt.%Mg alloy

Khalfallah, Ali; Raho, Azzeddine Abderrahmane; Amzert, Sid Ahmed; Djemli, Amar

doi:10.1016/s1003-6326(19)64932-0

Cited by 37 publications

(18 citation statements)

References 38 publications

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“…This is in conformity with recently published results, see References [19,20,31,32,58]. On the contrary, Figure 12b also shows weak spots which can be assigned to metastable η′-phase particles (see References [25,32,33]) and to the GP zones and secondary Al3(Sc,Zr)-phase particles [19,25,57,67]. Although the presence of the GP zones, T-, η′-and Al3(Sc,Zr)-phase particles has been demonstrated in electron diffraction ( Figure 12), the individual types of the particles could not be easily recognized in conventional TEM image thanks to the high density of the particles (Figure 11).…”

Section: Phase Development During Isochronal Annealingsupporting

confidence: 92%

“…Taking into account the behavior of the constituent (especially Zn, Mg, and Cu) at temperatures from RT to ~80 °C [20] and the calculated contribution of the solute concentration to the resistivity of Al (e.g., References [1,54,55]), the resistivity development during natural ageing is mainly associated with the change of Zn and Mg concentrations in the Al matrix. In the first approximation it can be assumed that the (co-)clusters/GP zones are composed of Zn and Mg atoms in a ratio of: (a) 1:1; (b) 1:2, see e.g., References [10,15,17,19,[20][21][22][23][24][25][26][27][28][29][30][31][32][33][56][57][58]]. If we assume this, then the resistivity Δρ changes in the HT + NA state (after natural ageing up to 3500 h), Δρ ≈ 8 nΩ•m, see Table 3, would correspond to the decrement of Zn-and Mg-concentration in the matrix: (a) ΔCZn,Mg ≈ 0.7 ± 0.1 at.%; (b) ΔCZn ≈ 0.8 ± 0.2 at.% and ΔCMg ≈ 0.4 ± 0.1 at.%.…”

Section: Natural Ageing Of the Heat-treated Alloysmentioning

confidence: 99%

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Role of Small Addition of Sc and Zr in Clustering and Precipitation Phenomena Induced in AA7075

Vlach

Kodetová

Čı́žek

et al. 2020

Metals

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A detailed characterization of phase transformations in the heat-treated commercial 7075 aluminum alloys without/with low Sc–Zr addition was carried out. Mechanical and electrical properties, thermal and corrosion behavior were compared to the microstructure development. The eutectic phase consists of four parts: MgZn2 phase, Al2CuMg phase (S-phase), Al2Zn3Mg3 phase (T-phase), and primary λ-Al(Mn,Fe,Si) phase. Strengthening during non-isothermal (isochronal) annealing is caused by a combination of formation of the GP zones, η’-phase, T-phase and co-presence of the primary and secondary Al3(Sc,Zr)-phase particles. Positive influence on corrosion properties is owing to the addition of Sc–Zr. Positron annihilation showed an evolution of solute Zn,Mg-(co-)clusters into (precursors of) the GP zones in the course of natural ageing. The concentration of the (co-)clusters is slightly negatively affected by the low Sc–Zr addition. A combination of both precipitation sequences of the Al–Zn–Mg–Cu-based system was observed. The apparent activation energy values for dissolution/formation of the clusters/GP zones and for formation of the metastable η’-phase, stable T-phase and stable η-phase were calculated.

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Section: Phase Development During Isochronal Annealingsupporting

confidence: 92%

Section: Natural Ageing Of the Heat-treated Alloysmentioning

confidence: 99%

Role of Small Addition of Sc and Zr in Clustering and Precipitation Phenomena Induced in AA7075

Vlach

Kodetová

Čı́žek

et al. 2020

Metals

View full text Add to dashboard Cite

show abstract

“…Khalfallah et al [ 56 ] found by DSC that the formation of GP region is controlled by the migration of Zn and Mg atoms, while η′ metastable and η precipitation of stable phase is affected by the migration and diffusion of solute atoms. Berg et al [ 57 ] found that GP I region was formed in a wide temperature range from room temperature to 140–150 °C, and was independent of quenching temperature.…”

Section: Aging Precipitation Sequence and Strengthening-toughening Me...mentioning

confidence: 99%

Review on Micro-Alloying and Preparation Method of 7xxx Series Aluminum Alloys: Progresses and Prospects

2022

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Notably, 7xxx series aluminum alloy has become the most popular nonferrous alloy, extensively used in industry, construction and transportation trades, due to its high comprehensive properties such as high static strength, high strength, heat resistance, high toughness, damage resistance, low density, low quenching sensitivity and rich resource. The biggest challenge for aluminum alloy today is to greatly improve the corrosion resistance of the alloy, while maintaining its strength. The preparation method of 7xxx series aluminum alloy requires controlling time lapses in the process of heating, holding and cooling, and there are many species precipitates in the crystal, but the precipitated strengthening phase is a single type of equilibrium η′ phase. Therefore, more attention should be paid to how to increase the volume fraction of η′ precipitates and modify the comprehensive performance of the material and focus more on the microstructure of the precipitates. This article reviews the progress of 7xxx series aluminum alloy materials in micro-alloying, aging precipitation sequence, the strengthening-toughening mechanism and the preparation method. The effect of adding trace elements to the microstructure and properties of 7xxx series aluminum alloy and the problems existing in aging precipitation characteristics and the reinforcement mechanism are discussed. The future development direction of 7xxx series aluminum alloy is predicted by developing a method for the process-microstructure-property correlation of materials to explore the characteristic microstructure, micro-alloying, controlling alloy microstructure and optimizing heat-treatment technology.

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“…This is even more doubtful if the DSC peaks are used for the determination of activation energies for the precipitation of specific phases, such as in many works, (e.g. [7][8][9][10][11][12][13][14][15]), for instance, by applying evaluation methods like the Kissinger method [16].…”

Section: Introductionmentioning

confidence: 99%

In situ high-energy X-ray diffraction of precipitation and dissolution reactions during heating of Al alloys

et al. 2021

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During heating of Al alloys, typically a sequence of precipitation and dissolution reactions occurs and the single (partly opposing) reactions superimpose. Differential scanning calorimetry (DSC) is one common technique to analyse the kinetic development of precipitation and dissolution in Al alloys, but the superposition of the exothermic precipitation and endothermic dissolution reactions complicates the DSC signal interpretation, as DSC measures the sum of any heat effect. Synchrotron high-energy X-ray diffraction (HEXRD) allows the kinetic development of phase transformations to be obtained and can support the separation of superimposed DSC signals. HEXRD results from this work offer a new approach to separate part of the superimposed reactions and their kinetic development for the equilibrium phases β-Mg2Si in EN AW-6082 and η-Mg(Zn,Cu,Al)2 in EN AW-7150. Comparing DSC and HEXRD results confirms serious overlap issues. Common DSC evaluation methods alone, using zero crossing between endothermic and exothermic heat flow or peak positions can be misleading regarding individual reaction start and finish temperatures as well as regarding reaction intensities, which can be unambiguously determined by in situ HEXRD.

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Precipitation kinetics of GP zones, metastable η′ phase and equilibrium η phase in Al−5.46wt.%Zn−1.67wt.%Mg alloy

Cited by 37 publications

References 38 publications

Role of Small Addition of Sc and Zr in Clustering and Precipitation Phenomena Induced in AA7075

Role of Small Addition of Sc and Zr in Clustering and Precipitation Phenomena Induced in AA7075

Review on Micro-Alloying and Preparation Method of 7xxx Series Aluminum Alloys: Progresses and Prospects

In situ high-energy X-ray diffraction of precipitation and dissolution reactions during heating of Al alloys

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