Effects of neutron irradiation on the stress relaxation rate in Al–Cu–Mg alloy

Neutron irradiation effects on the stress relaxation rate of Al–Cu–Mg alloy have been investigated. The specimens were exposed to 100 mC, Ra–Be neutron source of continuous energy 2–12 MeV for a period ranging from 4 to 16 days. Stress relaxation tests during the tensile tests at room temperature were performed at multiple stress levels up to the fracture using a universal testing machine. The comparison of the stress relaxation rate of irradiated specimens with that of an unirradiated one shows that the rate decreases after irradiation. The decrease becomes more pronounced as the exposure time increases. The activation energy to the movement of dislocations was found to be higher in irradiated specimens than in an unirradiated one. The analysis of results shows that the rate controlling process of stress relaxation in irradiated specimens is different from that of an unirradiated one. The micrographs of fractured surfaces in fact point to the changes that take place in the fracture mechanism before and after irradiation. These observations account for the decrease in the stress relaxation rate.