Constitutive modeling and microstructure research on the deformation mechanism of Ti-6Al-4V alloy under hot forming condition

Abstract

The hot tensile tests of Ti-6Al-4V alloy sheet at different temperatures (650, 700, 750 ℃) and different strain rates (0.1 s−1, 0.01 s−1, 0.001 s−1) were carried out, five phenomenological models are established (Arrhenius with strain compensation(ARR), Johnson-Cook(JC), modified JC(m-JC), Hensel-Spittel(HS), modify HS(m-HS)). A new JC model considers the softening coefficient m as a function of strain rate and adds a temperature correction function is proposed. The electron backscatter diffraction (EBSD) test was used to observe the microstructure evolution after thermal deformation at 700 ℃-0.1 s−1. After high-temperature tensile loading, the proportion of β phase increased, the average grain size decreased by 67.69%. The macroscopic softening phenomenon is caused by dynamic recrystallization (DRX), dynamic recovery (DRV), and the formation of β phase. The prediction accuracy of the six models was discussed by comparing the AARE value and the R-value. The comparison results show that the HS model has the best prediction accuracy, and its AARE value and R-value are 5.24% and 0.98794; the JC model has the worst prediction ability, and its AARE value and R-value are 41.1% and 0.84726. The prediction accuracy of the n-JC model is higher than that of the other JC models.