Guinier-Preston and Guinier-Preston-Bagaryatsky Zone Reversion in Al-Cu-Mg Alloys Studied by NMR
GP and GPB zone formation in Al-Cu-Mg alloys proceeds rapidly at room temperature immediately subsequent to STQ. This structure evolution is well known for GP zones but not for GPB zones. In many age-hardenable Al-Cu-Mg alloys this vacancy assisted diffusion of Cu from solid solution to form zones is essentially complete within 50 hours with only a small residual quantity of Cu remaining in solid solution. The alloy then remains in this metastable state. This zone formation is observed here using 63Cu NMR for the alloys AA2014 and AA2124 which lie in the α-θ (GP) and α-S (GPB) phase fields respectively. However these zones which form so readily at room temperature are unstable on aging at higher temperatures. Rapid dissolution of the zones, and their reversion back into solid solution at elevated temperatures is explicitly demonstrated by 63Cu nuclear magnetic resonance (NMR). At this stage the Cu is shown to remain stably in solid solution at room temperature. Further aging at the same elevated temperature is then shown to reform the zones with further continuous evolution to either the θ-phases (AA2014) or S-phase (AA2124).
W.J. Poole, M.A. Wells and D.J. Lloyd
T. J. Bastow and A. J. Hill, "Guinier-Preston and Guinier-Preston-Bagaryatsky Zone Reversion in Al-Cu-Mg Alloys Studied by NMR", Materials Science Forum, Vols. 519-521, pp. 1385-1390, 2006