Stress relaxation properties and microscopic deformation structure of H68 and QSn6.5–0.1 copper alloys at 353 K

Abstract

The stress relaxation tests in cantilever bending were performed on H68 and QSn6.5–0.1 at 353 K. The effect of low temperature stress-relief treatments on stress relaxation properties is investigated. The structural changes associated with the stress relaxation process were examined using scanning electron microscope (SEM) and transmission electron microscope (TEM). The test results show that the specimens subjected to the stress-relieved treatment of 523 K×1 h for H68 and 493 K×1 h for QSn6.5–0.1 have lower stress relaxation. An empirical formula σ=[K ln (t+a)+c] −n for stress relaxation data is given to fit the experimental stress relaxation curves by assuming the mobile dislocation density varying with the time as the hyperbola function. Microscopic analysis implies that the stress relaxation of copper alloys is characterized by the process of ordering and stabilizing of a dislocation structure. This process includes slipping, climbing and partly recovering. The stress relaxation mechanism is discussed, finally.