Early decomposition of supersaturated solid solutions of Al–Zn–Mg casting alloys

This study aimed at investigating the structural, electrical resistivity and hardness changes of aged Al–Zn–Mg alloys. It was observed that the isothermal annealing in temperature range of 25–200 °C leads to the following precipitation sequence: Guinier–Preston zones → η′-phase → η-phase. The significant increase of electrical resistivity (ρ) of the considered alloys was associated with the stage of GP zone decomposition. The formation of the intermediate η′-phase was accompanied with a decrease of electrical resistivity and an increase of hardness. Non-continuous quenching was found to suppress the η′-phase formation; while elevated quenching rates led to the formation of uniformly distributed fine precipitates in the alloy bulk.