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technical review & Discussion
An Evaluation of Quality Parameters for High Pressure Diecastings Part 2: Heat treatment R. Lumley, N. Deeva, CSIRO Future Manufacturing Flagship, Victoria, Australia
Authors: In response to reviewers’ notes in relation to the chemistry and precipitation sequence in Al-Cu alloy. The precipitation sequence in (binary) aluminium-copper alloys is currently believed to be:1 ·
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·
The form of θ” is a coherent precipitate, reported to have two layers of Cu atoms separated by three layers of aluminium atoms (, i.e. [Cu-Al- Al-Al]n
· The form of θ’ is a semicoherent tetragonal precipitate with chemistry Al2
stoichiometry of Al3Cu.2 Cu that forms on {100}α
Supersaturated solid solution (SSSS)GP zonesθ"θ'θ, where the θ phase is the equilibrium precipitate and the others are transitional phases formed during the decomposition of the solid solution.
·
of Cu atoms between adjoining layers of Al atoms, [Al-Cu-Al])
The form of GP zones is coherent, and usually forms as single layers (disks) of Cu atoms on substitutional sites of {100}α
. (i.e. a single layer . When cold work is applied to the
aluminium following solution treatment, θ’ forms directly on dislocations without forming GP zones or θ”.
· The (equilibrium) form of θ is an incoherent body centred tetragonal phase with chemistry of Al2
Cu.
1. Polmear, I.J., “Light Alloys: From Traditional Alloys to Nanocrystals”, 4th publishers, 2005, p.57.
ed. Butterworth-Heinemann
2. Bastow, T.J., Celotto, S., “Structure Evolution in Dilute Al(Cu) Alloys Observed by 63Cu NMR” Acta Materialia 51 (2003) pp.4621–4630.
, like 3-D stacked GP zones) and formal
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