The influence of magnesium impurity atoms on the annealing kinetics of low-temperature neutron-irradiated aluminum

Abstract

The influencc of magnesium atoms in stages II and III of aluminum are investigated from the recovery of the residual electrical resistivity of aluminum and a series of aluminum-magnesium alloys (nominally 0.02 –0.7 at %) at a total neutron dose of 9.10¹⁸ n/cm² at liquid nitrogen temperature. Isochronal annealing studies were performed for a temperature range 78 to 350°K with different heating rates (0.5 deg/min for 78-235°K and 1 deg/min for 245-345°K). Isothermal annealing for 215°K was carried out for a total period of 136 min. It was found that the annealing of stage III occurs by a second order process with an activation energy E=0.602 ± 0.03 eV for pure aluminum and the aluminum alloys. The consistency of this value with that obtained from quenching experiments is in favor of the vacancy motion model for the interpretation of the mechanism involved in stage III for aluminum and dilute aluminum alloys. Substages in both stage II (127 and 145°K) and stage III (190 and 245°K) are apparent. Substages of stage II are interpreted as being due to the break up of interstitials from impurity atoms. An interesting feature is the substage at the limits of stages III and IV, which appears in the alloys and increases with concentration in magnesium atoms. A mechanism consisting of the trapping of vacancy-type defects during their migation in stage III can explain the experimental results. A reverse electrical resistivity recovery, was observed at the high temperature limits of stage III and was attributcd to the formation of Guinier-Preston zones.