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 degrees C leads to the following precipitation sequence: Guinier-Preston zones -> eta'-phase -> eta-phase. The significant increase of electrical resistivity (rho) of the considered alloys was associated with the stage of GP zone decomposition. The formation of the intermediate eta'-phase was accompanied with a decrease of electrical resistivity and an increase of hardness. Non-continuous quenching was found to suppress the eta'-phase formation; while elevated quenching rates led to the formation of uniformly distributed fine precipitates in the alloy bulk. (c) 2013 Elsevier Ltd. All rights reserved.