Time evolution of the structure function of quenched Al-Zn and Al-Zn-Mg alloys

Abstract

The decomposition of Al–6.8 at. % Zn and Al–10 at. % Zn binary alloys and ternary alloys with the further addition of 0.1 at. % Mg, quenched into the miscibility gap and aged at different temperatures (18, 40, and 80 °C), has been studied by small-angle neutron scattering. The scattering cross section dΣ(k,t)/dΩ as a function of scattering vector k at different aging times t has been analyzed in terms of time-evolution theory of the structure function S(k,t), proposed by Furukawa, taking into account the scaling properties of S(k,t), the mobility M(t) of the clusters, and the diffusivity $D_T$(k,t) of a cluster gas. The results show that a simple dynamical scaling law S(k,t)∝R(t${)}^3$S̃(kR(t)) with a characteristic cluster size R(t)∝$t^a$ and a universal scaling function S̃(x)∝$x^2$/(γ/2+$x^{2+\gamma }$) holds for a wide range of aging times for various samples with different aging temperatures. From the analysis we could extract the time evolution of M(t) and $D_T$(k,t), which should determine the evolution of S(k,t), and thus we were able to calculate numerically the time evolution of dΣ(k,t)/dΩ in good agreement with corresponding observed quantities.