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Influence of different heat treatments on microstructure and stress rupture property of DZ951 alloy was investigated. The results show that the shape of carbide changes from script-like of as-cast alloy to blocky during heat treatment, which can prevent microcrack initiation and propagation at or near carbides. The stress rupture life of DZ951 alloy at 1100 degrees C/60 Wa increases with the rise of solution temperature until 1240 degrees C then it begins to decrease. The size of cuboidal gamma' phase and the volume of spherical gamma' phase increase with the rise of aging temperature. Bimodal gamma' phase is achieved at higher aging temperature. Better stress rupture property for DZ951 alloy may be obtained by reasonable combination of the size and volume fraction of cuboidal and spherical gamma' phase. The fractographs of DZ951 alloy at different conditions show a ductile fracture mode. (c) 2007 Elsevier B.V. All fights reserved.