Interplay of Chemistry and Faceting at Grain Boundaries in a Model Al Alloy

Zhao, Huan; Huber, Liam; Lu, Wenjun; Peter, Nicolas J.; An, Dayong; Geuser, F. de; Dehm, Gerhard; Ponge, Dirk; Neugebauer, Jörg; Gault, Baptiste; Raabe, Dierk

doi:10.1103/physrevlett.124.106102

Cited by 28 publications

(17 citation statements)

References 61 publications

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“…Grain boundary defects, such as ledges, may also act as preferential nucleation sites [46,49]. Zhao et al demonstrated how a grain boundary may decompose into facets with different segregation and precipitation behaviour [50]. The spacing between grain boundary particles may have influence on the presented SCC results, but the statistics from the methods used in this work could not be applied in drawing any conclusions related to this due to the enormous variations between grain boundaries within the same sample.…”

Section: Discussionmentioning

confidence: 92%

Stress Corrosion Cracking in an Extruded Cu-Free Al-Zn-Mg Alloy

Lervik

Walmsley

Lodgaard

et al. 2020

Metals

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Stress corrosion cracking (SCC) in Cu-free Al-Zn-Mg (7xxx) aluminium alloys limits its use in many applications. In this work, we study in detail the microstructure of a peak and slightly overaged condition in an AA7003 alloy using transmission- and scanning electron microscopy in order to provide a comprehensive understanding of the microstructural features related to SCC. The SCC properties have been assessed using the double cantilever beam method and slow strain rate tensile tests. Grain boundary particles, precipitate free zones, and matrix precipitates have been studied. A difference in the SCC properties is established between the two ageing conditions. The dominating difference is the size and orientation of the hardening phases. Possible explanations correlating the microstructure and SCC properties are discussed.

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Section: Discussionmentioning

confidence: 92%

Stress Corrosion Cracking in an Extruded Cu-Free Al-Zn-Mg Alloy

Lervik

Walmsley

Lodgaard

et al. 2020

Metals

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“…We recently reported on the interplay of chemistry and faceting at GBs in the same Al-Zn-Mg-Cu alloy [40] . The GBs show significant different segregation and precipitation behavior along the GB plane.…”

Section: Interplay Of Segregation and Local Structure At Gbsmentioning

confidence: 99%

Grain boundary segregation and precipitation in an Al-Zn-Mg-Cu alloy

et al. 2020

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High strength Al-alloys are highly susceptible to intergranular embrittlement, which severely limits their lifetime. This article summarizes our recent work on the effect of solute segregation in the precipitation behavior at grain boundaries (GBs) compared to the grain interiors. Solute segregation could accelerate the precipitation behavior at GBs, which causes the formation of coarse precipitates and precipitate free zones along GBs. Furthermore, the interplay of solute segregation and the local structure at GBs has been considered. We show that the distinct segregation and precipitation behavior occurs within the same GB, which makes the GB excess of solutes at one facet significantly higher than the other facet. This paper enriches the current understanding on the role of chemistry and structure at GBs related to intergranular fracture and corrosion resistance in high strength Al-alloys.

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“…This has resulted in intense efforts to characterise the GBs in 7xxx alloys at the atomic-scale using advanced techniques, such as aberration-corrected scanning transmission electron microscopy (STEM) [4,5,12] and atom probe tomography (APT) [10,11,13,14]. In recent work, on which we focus herein, APT revealed significant solute segregation to GBs, in a model as-quenched Al-Zn-Mg-Cu alloy [11,15], and a significant acceleration of the sequence of precipitation compared to that found in the bulk of the grains. Grain-size effects on segregation have also been investigated, with higher Zn segregation being observed in a coarse-grained alloy compared to in an ultrafine-grained alloy, while similar Mg and Cu segregation levels were observed [11,13,14].…”

Section: Introductionmentioning

confidence: 99%

CALPHAD-informed phase-field modeling of grain boundary microchemistry and precipitation in Al-Zn-Mg-Cu alloys

Liu

Garner²,

Zhao

et al. 2021

Preprint

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The grain boundary (GB) microchemistry and precipitation behaviour in high-strength Al-Zn-Mg-Cu alloys has an important influence on their mechanical and electrochemical properties. Simulation of the GB segregation, precipitation, and solute distribution in these alloys requires an accurate description of the thermodynamics and kinetics of this multi-component system. CALPHAD databases have been successfully developed for equilibrium thermodynamic calculations in complex multi-component systems, and in recent years have been combined with diffusion simulations. In this work, we have directly incorporated a CALPHAD database into a phase-field framework, to simulate, with high fidelity, the complex kinetics of the non-equilibrium GB microstructures that develop in these important commercial alloys during heat treatment. In particular, the influence of GB solute segregation, GB diffusion, precipitate number density, and far-field matrix composition, on the growth of a population of GB η-precipitates, was systematically investigated in a model Al-Zn-Mg-Cu alloy of near AA7050 composition. It is shown that the GB solute distribution in the early stages of ageing was highly heterogeneous and strongly affected by the distribution of GB η-precipitates. Significant Mg and Cu GB segregation was predicted to remain during overageing, while Zn was rapidly depleted. This non-trivial GB segregation behaviour markedly influenced the resulting precipitate morphologies, but the overall precipitate transformation kinetics on a GB were relatively unaffected. Furthermore, solute depletion adjacent to the GB was largely determined by Zn and Mg diffusion, which will affect the development of precipitate free zones during the early stages of ageing. The simulation results were compared with scanning transmission electron microscopy and atom probe tomography characterisation of alloys of the similar composition, with good agreement.

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Interplay of Chemistry and Faceting at Grain Boundaries in a Model Al Alloy

Cited by 28 publications

References 61 publications

Stress Corrosion Cracking in an Extruded Cu-Free Al-Zn-Mg Alloy

Stress Corrosion Cracking in an Extruded Cu-Free Al-Zn-Mg Alloy

Grain boundary segregation and precipitation in an Al-Zn-Mg-Cu alloy

CALPHAD-informed phase-field modeling of grain boundary microchemistry and precipitation in Al-Zn-Mg-Cu alloys

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