Low-temperature dynamic precipitation in a supersaturated AI-Zn-Mg alloy and related strain hardening

Dynamic precipitation during low-temperature deformation of a supersaturated Al-Zn-Mg alloy has been studied by small-angle X-ray scattering and in-situ resistivity in the temperature range 4.2–300 K. At 300 K, dynamic precipitation is observed both for the material strained in the form of a solid solution and for the material strained in the partially aged state, that is containing Guinier-Preston (GP) zones. In the first case, dynamic precipitation occurs by nucleation of precipitates 5 Å in diameter, and in the second case it occurs by coarsening of existing precipitates. In all cases the dynamic precipitation results in an unusual-strain hardening behaviour in which the work-hardening rate is very high and essentially temperature independent.