Cryogenic deformation behavior, constitutive modeling and microstructure evolution of solution-treated 2195 Al - Li alloy at high strain rates

In this paper, the flow behavior, constitutive model and microstructure evolution of solution-treated 2195 Al-Li alloy at temperatures from 123 K to 298 K and strain rates from 2000 s(-1) to 5000 s(-1) were studied. Experimental results show that the flow stress of the solution-treated 2195 Al-Li alloy is more sensitive to deformation temperature than strain rate. As the temperature declines from 298 K to 123 K, the flow stress at 2000 s(-1) and 5000 s(-1) increases by nearly 32.8% and 34.5%, respectively; whereas as the strain rate increases from 2000 s(-1) to 5000 s(-1), the flow stress at 298 K and 123 K only increases by 5.1% and 6.5%, respectively. The average strain hardening rate tends to decline with the increase in strain rate and temperature, and its value at 123 K and 2000 s(-1) is about 1.5 times greater than that at 298 K and 5000 s(-1). To overcome the very limited applicability of the conventional Arrhenius model with strain compensation, an Arrhenius-based model (c-Arrhenius model) is developed by coupling an independent strain term and then derived by using normalized flow stress and linear regression. To quantify the strain rate effect and temperature effect, a Johnson-Cook-based model (c-JohnsonCook model) with exponential terms is developed. These two new constitutive models are validated via a comparative analysis, showing good predictability and accuracy. A further microstructure observation shows that the dislocation density is the highest at a strain rate of 5000 s(-1) and cryogenic temperature of 123 K, which is beneficial for subsequent aging strengthening.