Experimental study on complex stress effect for stress relaxation aging behavior of Al-Cu-Li alloy

Abstract

The highlight of this work is to investigate the effect of complex initial stress levels (from elastic to plastic regions) on the Stress relaxation aging (SRA) behavior of T34-2195 Al-Cu-Li alloys. The uniaxial tensile SRA experiment with various initial stress levels was carried out at 180 °C for 16 h. A novel double stage relaxation behavior is observed and analyzed theoretically by X-ray diffraction peak-broadening (XRD) and transmission electron microscopy (TEM). When initial stress levels (the plastic region) are higher than the yield strength at 180 °C, the stress relaxation curves show the traditional single stage relaxation behavior. When initial stress levels (the elastic region) are lower than the yield strength, stress relaxation curves display four stages where a novel double stage relaxation behavior was observed, and four stages comprise the following parts: (1) the initial variable-rate and steady-rate relaxation stages; (2) the second variable-rate and second steady-state relaxation stages. The results show that a double stage relaxation behavior was scribed to the interaction among the dislocation, solute atoms and T1 (Al2CuLi) phase. The main reason for the difference between elastic and plastic initial stresses is the different dislocation density caused by the various initial stresses.