Strain-induced microstructural evolution and work softening behavior of Zn–15% Al alloy

Strain-induced microstructural evolution of a Zn–15% Al alloy was studied in order to elucidate the reason for its work softening behavior. Fully annealed microstructure of the Zn–15% Al alloy is distinctively characterized by primary η grains and (η + α) lamellar colonies, where η and α are Zn-rich HCP and Al-rich FCC phases, respectively. Hardness and yield strength decreased continuously with an increase in cold rolling up to 80%, exhibiting work softening behavior. During cold rolling, the (η + α) colonies with interlamellar spacing of ∼100 nm change into equiaxed η and α grains with sizes of ∼500 to ∼800 nm by dynamic recrystallization, whereas primary η grains are only elongated along the rolling direction without any evidence of recrystallization. A linear relationship between volume fraction of recrystallized (η + α) grains and the strength is established. The compositional analyses on primary η grains demonstrate that dissolved Al solutes inside η grains precipitate during cold rolling.