Hot deformation behaviors of AZ91 magnesium alloy: Constitutive equation, ANN-based prediction, processing map and microstructure evolution

Abstract

The hot deformation behavior in an AZ91 magnesium alloy was studied using Arrhenius model and Back-Propagation Artificial Neural Network (BP-ANN) approaches. The hot compression tests of AZ91 alloy were performed on the MMS-300 simulator at deformation temperatures and strain rates in the range of 473–623 K and 0.001 s −1 - 1 s −1 , respectively. The results indicated that the BP-ANN model has higher accuracy than Arrhenius model and the correlation coefficient is as high as 0.99341. The processing map is divided into three parts: machinable area (A), instability area I (INS I) (B) and instability area II (INS II) (C). The instability mode of areas B and C gradually changes from cracks to holes with the increase of temperature or the decrease of strain rate. The stable hot-deformation conditions with peak efficiency of power dissipation were concentrated in the range of 523 K, 0.01 s −1 , 573 K, 0.01 s −1 , 623 K, 0.001–1 s −1 , respectively. With the increase of temperature, the deformation mechanism changed from twinning to dynamic recrystallization (DRX), which is discontinuous dynamic recrystallization (DDRX). Due to DRX,< 0001 > // CD texture intensity increased with the increase of temperature, and then decreased. ● BP-ANN is used to predict stress and strain. ● Instability mode: crack and hole. ● Deformation mechanism: twinning, slip and DRX.