Hot deformation behavior of uniform fine-grained GH4720Li alloy based on its processing map

The hot deformation behavior of uniform fine-grained GH4720Li alloy was studied in the temperature range from 1040 to 1130℃ and the strain-rate range from 0.005 to 0.5 s⁻¹ using hot compression testing. Processing maps were constructed on the basis of compression data and a dynamic materials model. Considerable flow softening associated with superplasticity was observed at strain rates of 0.01 s⁻¹ or lower. According to the processing map and observations of the microstructure, the uniform fine-grained microstructure remains intact at 1100℃ or lower because of easily activated dynamic recrystallization (DRX), whereas obvious grain growth is observed at 1130℃. Metallurgical instabilities in the form of non-uniform microstructures under higher and lower Zener–Hollomon parameters are induced by local plastic flow and primary γ′ local faster dissolution, respectively. The optimum processing conditions at all of the investigated strains are proposed as 1090–1130℃ with 0.08–0.5 s⁻¹ and 0.005–0.008 s⁻¹ and 1040–1085℃ with 0.005–0.06 s⁻¹.