Anisotropy in creep-aging behavior of Al–Li alloy under different stress levels: experimental and constitutive modeling

Abstract

The anisotropy in creep aging behavior and microstructural evolution of AA2195-T34 A l–Li alloy plates under different stress levels at 180 °C were systematically investigated by constant-stress creep aging, mechanical property testing and microstructure characterization. The results indicated that the creep strain initially increases and then decreases with the angle relative to the rolling direction by cause of the divergences in the dislocation density and the number of movable sliding systems. The creep strain in 45° direction is 1.15 times and 1.41 times larger than that in 0° and 90° directions at a stress of 160 MPa, respectively. The creep strain in-plane anisotropy (IPA) value first increases rapidly, followed by a slight decrease with time, and declines with stress at the primary creep stage. The strength first increases and then tends to fluctuate around a constant value with the aging time because of the evolution of T1 precipitates. As shown by the gradual reduction in the difference among the volume fractions of the brass texture of the alloy in the three directions, the strength IPA rapidly declined at the primary creep stage. The IPA values of the yield strength during the steady creep stage are 4.8%, at a stress of 160 MPa. Since the Schmidt factor of the material in the 45° direction is the largest, the yield strength in this direction is the lowest. A constitutive model considering the anisotropy of creep deformation and aging strengthening was established, of which the predicted results showed excellent consistency with the experimental values. The relative errors between the predicted and experimental values of the yield strength/steady creep strain in different directions do not exceed 1.7% and 4.3%, respectively.

Keywords

• Al–Li alloy
• Creep-aging anisotropy
• Stress level
• Microstructural evolution
• Constitutive modeling