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 an d airframe manufacturers, the University of Virginia (WA) has been exa mining 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 th e supersonic Concorde. Microstructural evolution in the vicinity of th e grain boundaries of these alloys has been examined directly in the t ransmission electron microscope and by fracturing crept specimens at c ryogenic temperatures to expose grain facets. Variation in number dens ity and size of grain boundary precipitates as the severity of creep c onditions increases is related to creep behavior. (C) 1997 Elsevier Sc ience S.A.