Experimental study and modelling of anisotropic behaviour of aluminium-lithium alloys in creep age forming

Abstract

The anisotropic deformation behaviour of the 3rd generation aluminium-lithium (Al-Li) alloys can significantly affect the accuracy of prediction and fabrication, especially for fabricating complex shaped components. To address this challenge and shed light on improving the prediction accuracy with the existence of material anisotropy, this study systemically investigated the anisotropic behaviour during deformation and creep-ageing, and proposed a comprehensive anisotropic material model and its implementation method in the numerical simulation, which was verified with four-point bending creep age forming (CAF) tests. The anisotropic behaviours of the material including yielding, hardening, and creep deformation were investigated with uniaxial tensile and creep-ageing tests adopting specimens cutting along 0°, 15°, 30°, 45°, 70° and 90° to the rolling direction. The yield strengths varied in the range of 378 to 456 MPa for different directions, with the highest and lowest values appearing at 0° and 70°. The creep deformation also showed strong anisotropic behaviour and the accumulated creep strain for 90° (0.52%) was four times larger than the value for 0° (0.11%) under 415 MPa at 143 °C for 5 h An anisotropic material model was established based on the modified non-associated quadratic Hill48 yield function and can adequately capture the observed anisotropic behaviour. An implementation strategy using the bisection method with the map returning scheme was proposed for incorporating the proposed model in numerical simulation. A good agreement was achieved between the predicted and experimental results for four-point bending CAF tests, demonstrating the validity of the proposed anisotropic material model and the implementation method.