Investigation into thermodynamic behavior of LA103Z Mg[sbnd]Li alloy during turning based on modified Johnson–Cook model

Abstract

The LA103Z MgLi alloy is a promising lightweight material for aerospace applications due to its superior performance. Its machining involves a complex thermal–mechanical coupling process during which the material undergoes high strain rate deformation. Thus, determining the precise constitutive model for accurately modeling the cutting is extremely important. To analyze the material flow behavior, Split Hopkinson Pressure Bar (SHPB) tests were conducted under strain rates of 1200–5000 s−1. By observing the microstructural characteristics of the material, adiabatic temperature rise (ATR) is found to be the dominant factor affecting the flow stress. Accordingly, a modified Johnson–Cook (J–C) constitutive model was derived by considering the effects of ATR on thermal softening and strain rate strengthening terms. The modified model was validated by SHPB measure data, the average relative error is 3.08 %. The finite element (FE) model was established based on the modified J–C model to predict the turning behaviors at various parameters. The predicted values coincide well with measured results, which proving the high-precision of FE model. The analysis results of the thermodynamic behaviors under different cutting parameters of MgLi alloy shows that the influences of cutting speed on temperature, and depth of cut on cutting forces (main cutting force Fc and feed force Ff) are the most significant. However, the effect of cutting speed on the cutting force is not evident due to the effect of temperature rise. The reasonable turning conditions of the large depth of cut and feed rate, and small cutting speed was suggested for studied LA103Z MgLi alloy to consider the machining quality and efficiency.