Partial Reversion of Small GP Zones in an Al-Zn Binary Alloy

The reversion process of very small Guinier-Preston (GP) zones in Al-Zn binary alloys has been studied by time-resolved synchrotron-radiation small-angle X-ray scattering (SR-SAXS) measurements. Al-15 at.% Zn alloys with GP zones of 1.0 to 1.3 nm in radius formed by aging at 274 K were up-quenched up to 463 K. During reversion, the Guinier radius increased rapidly while the integrated intensity decreased. This rapid increase of the radius was completely different from what was found during the reversion of larger GP zones above the miscibility gap. It is concluded that a process of simultaneous dissolution and coarsening has been observed.