Aging phenomena in Al-Zn-Mg alloys ranging from (α+T) to (α+η) phase region

Abstract

Aging phenomena in Al-Zn-Mg alloys, ranging from (α+η) to (α+κ) phase regions, with 5 at% of Zn plus Mg were investiga ed by means of hardness, electrical resistivity and specific heat measurement and transmission electron microscopy. After solution treatment at 470°C for 1hr, specimens were quenched into iced water and aged at various temperatures between 50°C and 150°C. As the ratio, Zn/Mg, increased, the initial aging rate increased. However, at the same time, the distribution of G. P. zones and intermediate phases became coarser and the age-hardenability decreased. These observations were discussed in terms of the characteristcs of precipitates, present in the phase regions, and the solute-supersaturation which decreased with the increasing Zn/Mg ratio. The present study indicated, with the results reported in the previous study, that aging behavior of the (α+T) to (α+κ) type Al-Zn-Mg alloys changed continuously as the Zn/Mg ratio inc1eased, except in the (α+κ)type alloy, and the most excellent mechanical property was considered to be obtained by aging the Zn rich (α+T) type alloy at 125°C to 150°C.