Microstructural evolution in Al-Zn eutectoid alloy by hot-rolling

The Al-Zn eutectoid alloy has been widely known as a typical superplastic metallic material, where fine-grained microstructure is usually obtained by heat treatment. Recently, thermo-mechanical controlled process has also been reported to provide a fine-grained microstructure. In the present study, Al-Zn alloy ingots of 20 mm in thickness were homogenized and hot-rolled to a thickness of 2 mm under three processes: 1) the specimen was air-cooled after homogenization and hot-rolled; 2) the specimen was water-quenched after homogenization and hot-rolled; 3) the specimen was immediately hot-rolled after homogenization. Microstructural observation showed that, in processes 1 and 3, lamellar microstructure was formed after homogenization, and became fragmented to fine-grained microstructure as the hot rolling process proceeded. In process 2, fine-grained microstructure without lamellar microstructure was attained throughout the hot-rolling process. A minimum grain size of 1.6 μm was obtained in process 3. Tensile tests at room temperature showed that the elongation to failure was the largest in process 3.