Stress-dependent recovery of point defects in deformed aluminum: An acoustic-damping study

The stress dependence of point-defect diffusion to dislocations in a 99.99% polycrystalline aluminum was studied using shear-wave attenuation and phas e velocity. By holding the stress after deformation, attenuation and veloci ty approach their nonstressed values. The holding stress was varied between 0 and 12 MPa, after applying a 15 MPa compressive stress. Time-independent attenuation and stress-induced velocity change were introduced into the Gr anato-Hikata-Lucke theory, which first established the change of attenuatio n and velocity caused by the point-defect diffusion to dislocations. Good a greement was found between measurements and the modified theory. The stress dependence of the recovery rate was interpreted as a reduction of the migr ation energy of point defects diffusing to dislocations, and the activation volume was calculated for uniaxial stress. Electromagnetic acoustic resona nce (EMAR) was used for the measurements. Being noncontact and highly sensi tive, EMAR permitted detailed measurement of the attenuation and velocity e volutions during the unloading-holding stress sequence. Published by Elsevi er Science Ltd on behalf of Acta Merallurgica Inc.