Abstract:
The results of the experimental study of the formation kinetics of metastable phases during decomposition of supersaturated solid solutions of quenched Al–Mg–Si alloys are presented. The process has been studied by measuring the electrical conductivity at low temperatures (18–85$^\circ$C) and by measuring the Young’s modulus using the acoustic method in the temperature range 120–220$^\circ$C. The method of measuring the Young’s modulus is characterized by a high precision and has made it possible to distinguish between the successive stages of the decomposition due to the formation of Guinier–Preston zones, particles of the pre-$\beta''/\beta''$ and $\beta'$-phases. The effective activation energies have been calculated using the obtained data on the characteristic durations of the stages of the process at different temperatures. It has been shown that the activation energy of the formation and evolution of particles in the $\beta''$-phase is considerably lower than the activation energy of diffusion of alloying element atoms at equilibrium conditions, which is caused by the effect of long-lived quenching vacancies. This energy is close to the activation energy of migration of the $v$ + Mg complex and, according to the obtained results, is equal to 0.58 eV.
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