The Effect of Primary γ' Distribution on Grain Growth Behavior of GH720Li Alloy

Abstract

In this paper, a series of hot compression tests were carried out under different hot deformation parameters, covering the temperature range of 1000ºC to 1170ºC, strain rate range of 0.01s -1 to 1s -1 and compression reduction of 30%, 50%, and 70%. After that, all specimens were heat treated under the standard heat treatment schedule of GH720Li to investigate its hot deformation characteristics, especially the grain growth behaviors. The further OM and SEM observations were adopted to investigate the interaction mechanism of the primary γ′ distribution and grain growth for GH720Li alloy. The results show that for GH720Li alloy, when hot deformed below γ′ solvus, the banded or bi-model structure always occurs; while hot deformed near or over γ′ solvus, the uniform grain size distribution can be obtained. Further microstructure analysis shows that the bi-model or banded grain size distribution in GH720Li alloy is mainly due to the nonuniform re-dissolving of primary γ′ during heating process; while the uniformity of primary γ′ phase is determined by the uniformity of elements in this alloy. In other word, the homogenizing process for ingot is the key reason for later grain size control.