The structure of {111} age-hardening precipitates in Al–Cu–Mg–Ag alloys

Knowles, K. M.; Stobbs, W. M.

doi:10.1107/s0108768187012308

Cited by 197 publications

(73 citation statements)

References 12 publications

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“…The Ω phase has been previously proposed as monoclinic [29,30], hexagonal [31], orthorhombic [32] and tetragonal [33]. The above orientation relationships between Ω and matrix are consistent with one of 22 independent orientation relationships between θ and matrix (the orientation called 'Vaughan II' in [34]).…”

Section: Ssssupporting

confidence: 55%

VPPA welds of Al-2024 alloys: Analysis and modelling of local microstructure and strength

Wang

Lefebvre

Yan

et al. 2006

Materials Science and Engineering: A

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The microstructural features of variable polarity plasma arc welded Al-Cu-Mg 2024-T351 with 2319 filler have been studied by TEM, SEM and DSC. Fusion zone, partial melting zone, resolutionising zone, overageing (for S phase), peak ageing (for S phase) and under ageing zones (for S phase) have been identified. The Ω phase has been observed between re-solutionising zone and peak ageing zone. The hardness profile contains two peaks. The microstructure development, and resulting hardness and yield strength profiles are modelled using a model which combines primary precipitation, resolution, partial/full melting and resolidification (Scheil type) and reprecipitation, in a two precipitate -two mechanism approach. Hardness profiles and microstructures are accurately predicted. The hardness peak in the re-solutionising zone is due to re-solutionising and subsequent Cu-Mg co-cluster formation; and the second hardness peak is caused by S phase strengthening.

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Section: Ssssupporting

confidence: 55%

VPPA welds of Al-2024 alloys: Analysis and modelling of local microstructure and strength

Wang

Lefebvre

Yan

et al. 2006

Materials Science and Engineering: A

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“…103 In fact, Fig. 29a can also be obtained by the structures proposed by Auld, 101 Knowles and Stobbs 104 and Garg and Howe. 105 All the above SAD data indicate that the observations which led to the first three crystal structures described in Table 6 were in fact all on one single phase, possibly with very small differences in atomic coordinates.…”

Section: Phasementioning

confidence: 84%

“…701 nm (the fourth structure in Table 4). This pattern cannot be rationalised by the orthorhombic 104 or tetragonal 105 V structures, and hence should correspond to a different structure. However, the structure proposed by Kerry and Scott 103 cannot give an explanation for the streaks in the SAD patterns (indicated by arrows in Fig.…”

Section: Phasementioning

confidence: 99%

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Precipitates and intermetallic phases in precipitation hardening Al–Cu–Mg–(Li) based alloys

Wang¹,

Starink²

2005

International Materials Reviews

775

276

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. Although many suggestions for the existence of pre-precipitates in Al-Cu-Mg alloys with a Cu/Mg atomic ratio close to 1 have been made, a critical review reveals that evidence exists for only two truly distinct ones. The precipitation sequence is best represented as: supersaturated solid solutionRco-clustersRGPB2/S"RS where clusters are predominantly Cu-Mg co-clusters (also termed GPB or GPB I zones), GPB2/S" is an orthorhombic phase that is coherent with the matrix (probable composition Al 10 Cu 3 Mg 3 ) for which both the term GPB2 and S" have been used, and S phase is the equilibrium Al 2 CuMg phase. GPB2/S" can co-exist with S phase before the completion of the formation of S phase. It is further mostly accepted that the crystal structure of S' (Al 2 CuMg) is identical to the equilibrium S phase (Al 2 CuMg). The Perlitz and Westgren model for S phase is viewed to be the most accepted structure. 3DAP analysis showed that Cu-Mg clusters form within a short time of natural and artificial aging. Cu-Mg clusters and S phase contribute to the first and second stage hardening during aging. In Al-Cu alloys, the h phase (Al 2 Cu) has I4/ mcm structure with a50 . 607 nm and c50 . 487 nm, and h' phase with tetragonal structure and a50 . 404 nm, c50 . 58 nm, the space group is I4 m2. Gerold's model for h" (or GPII) appears to be favourable in terms of free energy, and is consistent with most experimental data. The transformation from GPI to GPII (or h") seems continuous, and as Cu atoms will not tend to cluster together or cluster with vacancies, the precipitation sequence can thus be captured as: supersaturated solid solutionRh" (Al 3 Cu)Rh' (Al 2 Cu)Rh (Al 2 Cu). The V phase (Al 2 Cu) has been variously proposed as monoclinic, orthorhombic, hexagonal and tetragonal distorted h phase structures. It has been shown that V phase forms initially on {111} Al with c50 . 935 nm and on further aging, the c lattice parameter changes continuously to 0 . 848 nm, to become identical to the orthorhombic structure proposed by Knowles and Stobbs (a50 . 496 nm, b50 . 858 nm and c50 . 848 nm). Other models are either wrong (for example, monoclinic and hexagonal) or refer to a transition phase (for example, the Garg and Howe model with c50 . 858 in a converted orthorhombic structure). For Al-Li-Cu-Mg alloys, the L1 2 ordered metastable d' (Al 3 Li) phase has been observed by many researchers. The Huang and Ardell model for T 1 phase (space group P6/ mmm, a50 . 496 nm and c50 . 935 nm), appears more likely than other proposed structures. Other proposed structures are perhaps due to the T 1 phase forming by the dissociation of Kn110m dislocations into 1/6n211m Shockley partials bounding a region of intrinsic stacking fault, in which copper and lithium enrichment of the fault produces a thin layer of the T 1 phase.

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“…The Ω phase has been commonly accepted as an orthorhombic [24] structure with lattice parameters of a = 0.496 nm, b = 0.859 nm, c = 0.848 nm. Ω phase formation has been reported to be stimulated by Ag and Si additions [10] and can form 2024 type alloys during a slow quench [25,26].…”

Section: Published In: Scripta Materialia 54 (2006) 287-291mentioning

confidence: 99%

Precipitation hardening in Al–Cu–Mg alloys revisited

2006

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Transmission electron microscopy, differential scanning calorimetry and hardness test have been used to study the precipitation sequence on artificial ageing of a stretched Al-Cu-Mg alloy.Two ageing temperatures at 190°C and 150°C for different times have been chosen. Some orthorhombic GPB2/S" is present in samples aged at 150°C for 48h, which is at the very start of the 2 nd stage of hardening. The combined experiments clearly show the second stage hardening is dominated by S phase, which forms a dense precipitation at the peak hardness stage, whilst no significant amounts of other phases or zones are detected.

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The structure of {111} age-hardening precipitates in Al–Cu–Mg–Ag alloys

Cited by 197 publications

References 12 publications

VPPA welds of Al-2024 alloys: Analysis and modelling of local microstructure and strength

VPPA welds of Al-2024 alloys: Analysis and modelling of local microstructure and strength

Precipitates and intermetallic phases in precipitation hardening Al–Cu–Mg–(Li) based alloys

Precipitation hardening in Al–Cu–Mg alloys revisited

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