Hot Deformation Behavior and Hot Rolling Properties of a Nano-Y2O3 Addition Near-α Titanium Alloy

The hot deformation behavior and hot rolling based on the hot processing map of a nano-Y2O3 addition near-α titanium alloy were investigated. The isothermal compression tests were conducted at various deformation temperatures (950⁠–1070 °C) and strain rates (0.001–1 s−1), up to a true strain of 1.2. The flow stress was strongly dependent on deformation temperature and strain rate, decreasing with increased temperature and decreased strain rate. The average activation energy was 657.8 kJ/mol and 405.9 kJ/mol in (α + β) and β region, respectively. The high activation energy and peak stress were contributed to the Y2O3 particles and refractory elements comparing with other alloys and composites. The deformation mechanisms in the (α + β) region were dynamic recovery and spheroidization of α phase, while the β phase field was mainly controlled by the dynamic recrystallization and dynamic recovery of β grains. Moreover, the constitutive equation based on Norton–Hoff equation and hot processing map were also obtained. Through the optimal processing window determined by the hot processing map at true strains of 0.2, 0.4 and 0.6, the alloy sheet with multi-pass hot rolling (1050 °C/0.03–1 s−1) was received directly from the as-cast alloy. The ultimate tensile strength and yield strength of the alloy sheet were 1168 MPa and 1091 MPa at room temperature, and 642 MPa and 535 MPa at 650 °C, respectively, which performs some advantages in current research.

Constitutive Equation and Hot Processing Map for Tensile Test of Mg-13Gd-4Y-2Zn-0.5Zr Alloy at Elevated Temperature

The high temperature tensile behavior of Mg-13Gd-4Y-2Zn-0.5Zr alloy was investigated at deformation temperature of 400-520 °C and strain rate of 0.001-0.5 s-1, and the stress-strain curves were obtained by using INSTRON 3382. The high temperature tensile constitutive model and hot processing map of the alloy were established, and the reliability of the hot processing map was further verified by analyzing the microstructure of the deformed alloy. The results showed that the dynamic recrystallization (DRX) occurred of Mg-13Gd-4Y-2Zn-0.5Zr alloy during the tensile tests under high temperature conditions, and its peak stress decreased with the increase of deformation temperature or strain rate. The Arrhenius equation can be used to fit the rheological behavior of the alloy. The thermal deformation activation energy Q was 259.13kJ/mol, and the maximum error between the model and the experimental data was less than 9%. It can be concluded that the optimum deformation parameters of the alloy were temperature of 500-520 °C and strain rate of 0.01-0.001 s-1 based on the dynamic material model and hot processing map.