Decomposition of the solid solution in unrecrystallized plates of Al?Zn?Mg?Mn?Zr alloy

Abstract

1. We plotted isothermal transformation diagrams of an Al−Zn−Mg−Mn−Zr alloy, which show that decomposition of the solid solution is more rapid in unrecrystallized than in recrystallized plates of the alloy. Transmission electron microscopic examination indicates that the high rate of decomposition of the supercooled solid solution in unrecrystallized plates is due to the well-developed network of subgrain boundaries, promoting nucleation and growth of secondary phase during aging. 2. Unrecrystallized plates age more rapidly than recrystallized plates at temperatures of 100–200o. On aging at temperatures below ∼140o the strengthening effect is higher in unrecrystallized than in recrystallized plates, while at higher temperatures it is lower. 3. The strength characteristics of artificially aged plates with an unrecrystallized structure are more sensitive to the time interval between quenching and artificial aging than in the case of phates with a recrystallized structure.