The effect of thermal excursions on the strength of aluminum alloys 6061 and 7075

Abstract

The effect of various thermal excursions on the strengths of the aluminum alloys 6061-T6 and 7075-T73 has been studied. The excursions were representative of those anticipated for an aerospace vehicle during a mission. Slow temperature changes were produced in samples of each alloy by closed-loop joule heating, and rapid in-depth heating was produced by pulsed electron beams. Results show that thermal environments which increase the thermodynamic stability of the strengthening phases also tend to decrease the sensitivity of the alloys to strength degradation by rapid heating. This behavior is explained in terms of the kinetics of coarsening of the metastable second phase particles. A relationship is derived which permits prediction of strength as a function of thermal history, and the activation energies for particle coarsening determined using this relation compare favorably with values taken from the literature.