Study on dynamic recrystallization and precipitation behavior of hot compressed Al-20Zn-0.5Mg-0.5Sc alloy

Abstract

The dynamic recrystallization (DRX) behavior of the Al-20Zn-0.5Mg-0.5Sc alloy was investigated under specific conditions using a Gleeble-3500 thermal simulator. The resultant grain size, recrystallization degree and precipitated phases were studied. The results indicate that the sensitivity of DRX grain size is highly affected by temperature, feebly influenced by strain and intermediately affected by strain rate. The DRX grains are grown by an average of 3.49 μm with increasing temperature. The DRX behavior is sensitive to temperature, strain and strain rate, resulting in changes in average grain size, percentage of HAGBs and degree of recrystallization under different parameters. At 400 ℃ / 40 % / 0.1 s−1, the average grain size is refined to 12.90 μm, and the corresponding HAGBs and recrystallization degree are approximately 46.2 % and 34.3 %, respectively. The Al3Sc, Zn and η (MgZn2) phases are precipitated in the hot-compressed alloy. The Al3Sc phase promotes the precipitation of the Zn and η phases. The size, amount and morphology of Al3Sc, Zn and η phases at different parameters have an important influence on the movement of dislocations and nucleation of grains, which leads to changes in DRX grain size and the degree of recrystallization. The fine precipitated phase particles Al3Sc and η inhibit the growth of recrystallized grain by pinning grain boundaries and exerting a blocking force on dislocations. Dynamic precipitation is the dominant mechanism for the changes in DRX grain size and degree of recrystallization. To achieve the refined grains and homogeneous microstructures, the optimum parameters are recommended as 400 ℃, 0.1 s−1 and 50 %.