Hot deformation behavior and processing map of a new type Mg-6Zn-1Gd-1Er alloy

Abstract

The hot deformation behavior of a new type Mg-6Zn-1Gd-1Er alloy was investigated in the temperature range of 180 ℃–380 ℃ and strain rate of 10−3 s−1–10 s−1 with the Gleeble-3500 thermal simulation testing machine. The true stress-strain curves showed that flow stress increased with the increasing of strain rate and decreasing of temperature. The constitutive equations based on hyperbolic sine equation were used to demonstrate the flow stress of two intervals of medium-high and low temperature deformation for this alloy. Processing maps were developed based on the experimental data of true strains of 0.2, 0.4, 0.6 and 0.8, which the optimal processing parameters were determined as 330 ℃–380 ℃ and 0.001 s−1–0.1 s−1. Microstructure analysis based on the strain rate corresponding to peak efficiency of power dissipation of processing map found that twinning was the dominate deformation mechanisms during low temperature deformation. With the increasing of temperature, a typical necklace-typed microstructure resulted by continuous dynamic recrystallization (CDRX) was formed. When the temperature was up to 380 ℃, the electron backscatter diffraction (EBSD) results of stable region showed that a typical discontinuous dynamic recrystallization (DDRX) and CDRX were the main deformation mechanisms, and formation a strong<0001>//CD texture together with secondary weaker texture component. At the instability region, it can be found that CDRX and twinning were the main deformation mechanisms, and an obvious bimodal texture formed at 380 ℃/10 s−1.