Atomic scale HAADF-STEM study of η′ and η
                     1 phases in peak-aged Al–Zn–Mg alloys

Bendo, Artenis; Matsuda, Kenji; Lee, Seungwon; Nishimura, K.; Nunomura, Norio; Toda, Hiroyuki; Yamaguchi, Masatake; Tsuru, Tomohito; Hirayama, Kyosuke; Shimizu, Kazuyuki; Gao, Haijun; Ebihara, Ken-ichi; Itakura, Mitsuhiro; Yoshida, Tomoo; Murakami, Satoshi

doi:10.1007/s10853-017-1873-0

Cited by 71 publications

(37 citation statements)

References 34 publications

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“…The lightweight AA7050 (Al-Zn-Mg-Cu) aluminium alloy possesses high strength owing to precipitate hardening [1]. The precipitation sequence for such aluminium alloys has been reported [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] as follows: super-saturated solid solution (SSSS) → GP zones (GP I and II [2][3][4][5][6]) → η' precipitates (4 variants [2,[7][8][9][10]) → η precipitates (11 types, η1-η11 [1,2,7,8,[11][12][13][14][15]). Recently, Chung et al [7], who identified GPII zones, η', and η2 precipitates in AA7050 aluminium alloy by high-resolution transmission electron microscopy (HRTEM), have elucidated the transition mechanisms of GPII zone → η' precipitate and η' precipitate → η2 precipitate.…”

Section: Introductionmentioning

confidence: 99%

“…Recently, Chung et al [7], who identified GPII zones, η', and η2 precipitates in AA7050 aluminium alloy by high-resolution transmission electron microscopy (HRTEM), have elucidated the transition mechanisms of GPII zone → η' precipitate and η' precipitate → η2 precipitate. Bendo et al [11], Marioara et al [18], and Xu et al [19] have analyzed the stacking structures in the η1 and η2 types on the atomic scale by Cs-corrected high-angle annular-darkfield (HAADF) scanning-transmission electron microscopy (STEM). However, the structures and the growth mechanisms of η-type precipitates on the atomic scale have not yet been completely elucidated.…”

Section: Introductionmentioning

confidence: 99%

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An atomic scale structural investigation of nanometre-sized η precipitates in the 7050 aluminium alloy

et al. 2019

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Using high-angle-annular-dark-field (HAADF) scanning-transmission-electron microscopy (STEM), we have investigated η-precipitates in the Al-Zn-Mg-Cu (AA7050) aluminium alloy. The HAADF STEM images taken along the zone axes of [101 ̅ 0]η, [12 ̅ 10]η, and [0001]η illustrated the projected atomic-scale configurations of η-MgZn2 crystal. The precipitates developed in layer-by-layer growth, supplied with precursors such as Zn, Cu, and Mg, which were solute atoms segregated around the η/Al interfaces due to the higher lattice strain energy. Stacking faults and defect layers composed of flattened hexagons were frequently observed along the zone axes of [12 ̅ 10]η and [101 ̅ 0]η, respectively, and their formation was elucidated, similarly taking into account the layer-by-layer growth. Occasional coalescence between two precipitates yielded a complicated boundary or a twin-like boundary.Based on the differences in orientation relationships between η-types and the Al matrix reported to date, two new types of η precipitates have been recognized and named η4' and η12.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

An atomic scale structural investigation of nanometre-sized η precipitates in the 7050 aluminium alloy

et al. 2019

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“…A combined high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and first-principles calculations study concluded that h ′ phase incorporates structural units present in η 2 -MgZn 2 Laves phase and both are bounded by the {111} Al interface planes enriched with heavy solute atoms [19]. The η 1 internal structure was found to incorporate some different arrangements of atomic structures, deviating from the stacking of (0001) MgZn 2 structure planes [20]. Furthermore, a cross-section of needle-like precipitates along 〈112〉 Al which do not fall into any particular orientation relationship was observed to incorporate Mg 6 Zn 7 elongated hexagons [21].…”

Section: Introductionmentioning

confidence: 99%

Characterisation of structural similarities of precipitates in Mg–Zn and Al–Zn–Mg alloys systems

Bendo

Maeda

Matsuda

et al. 2019

Philosophical Magazine

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High angle annular dark field scanning transmission electron microscopy has been employed to observe precipitate structures in Al-Zn-Mg and Mg-Zn alloys. h 1 precipitate structures in Al-Zn-Mg are commonly formed by MgZn 2 Penrose bricks, but also frequently observed to incorporate Mg 6 Zn 7 elongated hexagons via two different modes. Tilings of MgZn 2 and Mg 6 Zn 7 building blocks in both b ′ 1 in Mg-Zn and h 1 in Al-Zn-Mg alloys, create overall patterns which deviate from the chemical and structural configuration of solely monoclinic Mg 4 Zn 7 or MgZn 2 unit cells. Precipitate morphologies were found to be correlated to their internal sub-unit cell arrangements, especially to Mg 6 Zn 7 elongated hexagons. Systematic or random arrangements of Mg 6 Zn 7 elongated hexagons inside precipitates and therefore compositional and structural patterns, were found to be strongly related to the aspect ratio of the precipitates and altering of the precipitate/matrix interfaces.

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“…13) High-Angle Annular Dark Field Scanning Transmission Electron Microscope (HAADF-STEM) characterization along [110] Al showed that except ©A/© 2 phases, © 1 was the second most found precipitate in peak-aged AlZnMg samples and it incorporated different atomic arrangements from that commonly observed in ©A/© 2 phases. 14) Some age-hardenable AlMgSi, AlMgGe, and AlZnMg alloys including Cu were also investigated by TEM to understand extra diffraction spots that appear in their SAED patterns. The initial cluster, which is based on the ¢AA-phase in the AlMgSi alloy, is proposed to be MgSi(/Ge)Mg, CuMgSi(/Ge), AlCuMg, and AlZnMg, while the second clusters, which consist of three initial clusters including anti-phase boundary short-range order, are proposed for Cu-containing alloys.…”

Section: Introductionmentioning

confidence: 99%

Effect of Copper Addition on Precipitation Behavior near Grain Boundary in Al–Zn–Mg Alloy

et al. 2019

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The effect of Cu-addition on age-hardening and precipitation have been investigated by hardness measurement, tensile test, high resolution transmission electron microscopy (HRTEM) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) techniques. Higher hardness, strength, and lower elongation were caused by increasing amount of Zn + Mg because of increased number density of precipitates. Cu addition also provided even higher peak hardness, strength, and lower elongation. The alloy containing highest Cu content had fine precipitates of GPB-II zones or the second clusters, in the precipitate free zones (PFZs) and the matrix, together with ©A/© in the matrix from the early stage of aging. Two regions have been confirmed as the PFZs in the peak aged alloy containing highest Cu: (i) nearest to grain boundary (GB) about 70 nm in width (n-PFZ) and (ii) conventional PFZ about 400 nm in width which can be confirmed by conventional TEM (con-PFZ). The con-PFZ contains fine precipitates consisting of GPB-II zones or the second clusters, even for 2 minutes of aging at 473 K which were not present in the n-PFZ. The fine precipitates, GPB-II zones or the second clusters in the con-PFZ and the matrix disappeared at overaged condition.

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Atomic scale HAADF-STEM study of η′ and η 1 phases in peak-aged Al–Zn–Mg alloys

Cited by 71 publications

References 34 publications

An atomic scale structural investigation of nanometre-sized η precipitates in the 7050 aluminium alloy

An atomic scale structural investigation of nanometre-sized η precipitates in the 7050 aluminium alloy

Characterisation of structural similarities of precipitates in Mg–Zn and Al–Zn–Mg alloys systems

Effect of Copper Addition on Precipitation Behavior near Grain Boundary in Al–Zn–Mg Alloy

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