AA7050 Alloy

Alloy name: AA7050
Diagram No.: 859
Type of diagram: TTT
Chemical composition in weight %: 6.2% Zn, 2.3% Cu, 2.35% Mg, 0.13% Zr, balance is Al
Alloy group: Aluminium-based alloys
Note: Time Temperature Transformation curves for AA7050 showing the time required for precipitation of 1% S, 0.001% Eta and 0.0005% T.
The numerical model was also used to predict the Time Temperature Transformation curves. Isothermal cases were run at several temperatures to note the precipitation volume fractions. Figure shows the TTT curve for the precipitated S, Eta and T phases for AA7050 alloy. The red hollow circles indicate the time required to precipitate a volume fraction of 1% S during isothermal treatment in the temperature range of 250-450°C. As mentioned earlier the CCC also suggest very fast quenching in this temperature range to avoid S phase precipitation.
The Eta phase precipitates in the temperature range of 150-350°C, with the nose of the curve lying at approximately 275°C. The aging heat treatment is done to form fine metastable Eta’ phase precipitates prior to the stable Eta precipitates. However, at this temperature, Eta’ grows fast enough to transform into undesirable coarse stable Eta precipitates. Eta’ precipitation also is accompanied simultaneously by the undesirable T phase precipitates,occurring in the temperature range of 150-250°C. At temperature of 100-125°C, the TTT curve for Eta lies ahead of the curve for T phase. In this temperature range, supersaturation is high enough to precipitate numerous fine-sized metastable Eta’ precipitates without precipitation of the T phase. This temperature range is hence ideal for aging of these alloys.
Reference: Not shown in this demo version.

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