Non-isothermal “retrogression and re-ageing” treatment schedule for AA7055 thick plate

• Isothermal retrogression behavior of AA7055 grain boundary precipitate was given.
• The coarsening activation energy was obtained as 115.2 ± 1.3 kJ/mol.
• The RRA route of AA7055 thin plate was established.
• Non-isothermal retrogression model for AA7055 GBP was established.
• The applicative RRA route of AA7055 thick plate was established.

In order to apply the retrogression and re-ageing (RRA) treatment to AA7055 thick plate subject to the non-isothermal retrogression condition, a kinetic model based on the mean size evolution of grain boundary precipitate (GPB) is developed firstly. An optimized RRA treatment schedule derived from AA7055 thin plate is established subsequently. Taking the retrogression temperature and time as the references, the “equivalent retrogression time” in selected non-isothermal retrogression schedule of AA7055 thick plate was predicted by the kinetic model for several thermal paths with different heating rates. The efficiencies in processing and enhancements in strength that may be realistically achieved are also examined. The results reveal that, the “equivalent retrogression time” of the selected non-isothermal retrogression schedules can be predicted successfully. The similar properties to those from the referential RRA treatment can be achieved by more than one non-isothermal RRA schedule. However, the thick plate under non-isothermal retrogression schedule with quick heating rate could achieve the same properties by less energy consumption.

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