A 2xxx aluminum alloy crept at medium temperature: role of thermal activation on dislocation mechanisms

Fuselage skin of the future supersonic civil transport aircraft requires a material resistant to long-term creep at temperatures ranging from 100 to 130 °C. A candidate is the 2650 aluminum alloy which presents such properties at relatively high temperatures (130 °C=0.43Tmelting). From an accelerated creep test conducted at 150 °C under a 280 MPa load and subsequent observations of the dislocation microstructures by transmission electron microscopy, the role of thermal activation on dislocation mechanisms is analyzed. It appears that thermal activation favors cross-slip activity and allows dislocations to glide in non-close-packed planes, namely the {0 0 1} planes. This is the first time that evidence of primary {0 0 1} glide is reported. Associated to a strain-assisted decrease of the precipitate density, thermal activation softens the material and seems to contribute to the acceleration of the strain rate (tertiary stage) by facilitating bypassing of precipitates and the production of mobile dislocations. The different creep stages are explained in terms of individual dislocation mechanisms and not by referring to the evolution of dislocation substructures.