Creep behavior and microstructural stability of Al-Cu-Mg-Ag and Al-Cu-Li-Mg-Ag alloys

To assist in the development of a high speed civil aircraft by NASA and airframe manufacturers, the University of Virginia (UVA) has been examining the creep behavior of several candidate aluminum alloys. Under stresses and temperatures predicted to be experienced when cruising at Mach 2.0, measured creep strains of alloys C415, C416 and ML377 fall far below those of alloy 2618 (CM.001) which is currently in use on the supersonic Concorde. Microstructural evolution in the vicinity of the grain boundaries of these alloys has been examined directly in the transmission electron microscope and by fracturing crept specimens at cryogenic temperatures to expose grain facets. Variation in number density and size of grain boundary precipitates as the severity of creep conditions increases is related to creep behavior.