Effect of Cooling Rate after Solution Heat Treatment on Aging Properties of Al–Zn–Mg Alloy

This paper investigated the effect of cooling rate after solution heat treatment and pre-aging at 303 K after cooling on aging behavior of Al–6 mass%Zn–0.75 mass%Mg alloy to elucidate the aging behaviors and strengthening mechanism throughout aging heat treatment in the case of low cooling rate, such as furnace cooling, followed by solution heat treatment. Regardless the absence of pre-aging, the maximum hardness obtained in the materials with furnace cooling after solution treatment was almost the same as that of water-cooled and pre-aged materials during the same aging time. The result of microstructure observations using transmission electron microscope show that fine precipitates consisting of η phase have been formed in all peak-aged materials.