Atomistic details of precipitates in lean Al–Mg–Si alloys with trace additions of Ag and Ge studied by HAADF-STEM and DFT

Mørtsell, Eva Anne; Andersen, Sigmund Jarle; Friis, Jesper; Marioara, Calin Daniel; Holmestad, Randi

doi:10.1080/14786435.2017.1281461

Cited by 30 publications

(32 citation statements)

References 29 publications

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“…The quaternary GBP has a lattice parameter larger than that of Q′ phase in Al-Mg-Si-Cu alloys. E. A. Mørtsell [34] and T. Saito [30] Although the influence of Ag on the precipitation of Al-Mg-Si alloys has been investigated by different researchers, most of these works focus on one single precipitate (such as β′ phase) in a given aging condition.…”

Section: Introductionmentioning

confidence: 99%

Effect of Ag addition on the precipitation evolution and interfacial segregation for Al–Mg–Si alloy

et al. 2019

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The effect of Ag addition on the precipitation evolution and interfacial segregation for Al-Mg-Si alloys was systematically investigated by atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), atom probe tomography (APT) and density functional theory (DFT) calculation. At the early aging stage, Ag atoms could enter clusters and refine the distribution of these clusters. Then, Ag atoms preferentially segregate at the GP zone/α-Al and β"/α-Al interfaces at the peak aging stage by the replacement of Al atoms in FCC matrix. With prolonging aging time, Ag atoms generally incorporate into the interior of β" precipitate, facilitating the formation of QP lattice (a hexagonal network of Si atomic columns) and the local symmetry substructures, Ag sub-unit (1) and Ag sub-unit (2). At the over-aged stage, the Ag sub-unit (1) and Ag sub-unit (2) could transform to the β′Ag (i.e. β′Ag1 and β′Ag2.) and Q′Ag unit cells, respectively. All the precipitates at the over-aging stage have a composite and disordered structure due to the coexistence of different unit cells (β′Ag1, β′Ag2, Q′Ag and β′) and the non-periodic arrangement of Ag atoms within the precipitate. In the equilibrium stage, the incorporated Ag atoms in the precipitates release into the α-Al matrix as solute atoms or form Ag particles. In general, Ag atoms undergo a process of "segregate at the precipitate/matrix interface → incorporate into the interior of precipitate → release into the α-Al matrix" during the precipitation for Al-Mg-Si-Ag alloys. Besides, Ag segregation is found at the interfaces of almost all metastable phases (including GP zone, β″, β′/ β′Ag phase) in Al-Mg-Si-Ag alloys. The Ag segregation at the β′/α-Al interface could increase the length/diameter ratio of β′ phase and thus promote the additional strengthening potential of these alloys. These findings provide a new route for precipitation hardening by promoting the nucleation and morphology evolution of precipitates.

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Section: Introductionmentioning

confidence: 99%

Effect of Ag addition on the precipitation evolution and interfacial segregation for Al–Mg–Si alloy

et al. 2019

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“…It has been demonstrated that the enhanced age hardening response of Al-Mg-Si alloys by microalloying with various elements is closely related to the modified precipitation sequence [9,[12][13][14][18][19][20]. For example, Cu can suppress the precipitation of β" and facilitate the formation of Cu-containing precipitates (e.g.…”

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confidence: 99%

“…Q', C and L [1]) [9,18]. Ge atoms were reported to substitute some of the Si atoms in β" due to the similar electronic properties between Ge and Si [12,19]. Li preferentially occupies Mg3 sites in the β" structure [14].…”

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confidence: 99%

“…Ag atoms are often observed at the incoherent precipitate/matrix interfaces or incorporated into β' precipitates by replacing certain Si atomic columns [21,22]. Recently, a new Q'/C-like local configuration containing Ag at the Cu sites was discovered [19]. In addition, with the alloying additions, precipitates with disordered structures will become more common [13,19,23].…”

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Improving ageing kinetics and precipitation hardening in an Al-Mg-Si alloy by minor Cd addition

et al. 2018

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This study reports significant improvements in both the age hardening kinetics and peak hardness of an Al-Mg-Si alloy by microalloying with 0.06 at.% Cd. A detailed high-angle annular dark-field scanning transmission electron microscopy study shows that most of the needle-shaped hardening precipitates β" (~82%) formed in the Cd-containing alloy are attached to or around Cd-rich precipitates, indicating that the Cd-rich precipitates can act as effective nucleation sites for needle-shaped precipitates, and therefore substantially increase the number density and decrease the size of needle-shaped precipitates. It also shows that most of the β" precipitates in the Cd-containing alloy have a disordered structure, even at the peak-aged state.Additionally, Cu and/or Cd atoms are found to be incorporated into β" and some precipitates with Q'/C-like triangular sub-units are formed, which are very rare in Al-Mg-Si alloys with a trace Cu content of 0.01 wt.%.

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“…One unit cell has two such Si4Mg4-xAl2+x units at the (00z) and (½, 0, z+½) special positions in the unit cell. They may be regarded as molecular units of β" and were recently shown to come in three different stacking variations [11], sometimes mixed. The stacking variations occur particularly frequently with small additions of Ge, where Ge (partially) occupies some Si columns.…”

Section: Introductionmentioning

confidence: 99%

The effects and behaviour of Li and Cu alloying agents in lean Al-Mg-Si alloys

Mørtsell

Marioara

Andersen

et al. 2017

Journal of Alloys and Compounds

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We show how replacing a fraction of Mg with Li in a lean Al-Mg-Si alloy gives comparable strength and enhanced temperature stability. Replacing solute with smaller amounts of Cu and Li also improves thermal stability and nearly compensates the strength loss for longer ageing times. High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) documented Li and Cu causing modest structural changes to the main hardening precipitate, β". However, density functional theory calculations verified the observation from HAADF-STEM that Li preferentially occupies Mg3 sites in the β" structure.

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Atomistic details of precipitates in lean Al–Mg–Si alloys with trace additions of Ag and Ge studied by HAADF-STEM and DFT

Cited by 30 publications

References 29 publications

Effect of Ag addition on the precipitation evolution and interfacial segregation for Al–Mg–Si alloy

Effect of Ag addition on the precipitation evolution and interfacial segregation for Al–Mg–Si alloy

Improving ageing kinetics and precipitation hardening in an Al-Mg-Si alloy by minor Cd addition

The effects and behaviour of Li and Cu alloying agents in lean Al-Mg-Si alloys

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