MICROSTRUCTURE, TENSILE DEFORMATION AND FRACTURE-BEHAVIOR OF ALUMINUM-ALLOY-7055

The microstructure, tensile deformation and fracture behaviour of alum inium alloy 7055 were studied. Detailed optical and electron microscop y observations were made to analyse the as-received microstructure of the alloy. Detailed transmission electron microscopy observations reve aled the principal strengthening precipitates to be the hexagonal disc -shaped eta' phase of size 2 mm x 20 mm and fully coherent with the al uminium alloy matrix, the presence of spheroidal dispersoids, equilibr ium grain-boundary eta precipitates and narrow precipitate-free zones adjacent to grain-boundary regions. It is shown that microstructural c haracteristics have a profound influence on tensile deformation and fr acture behaviour. Tensile test results reveal the alloy to have unifor m strength and ductility in the longitudinal and transverse orientatio ns. Strength marginally decreased with an increase in test temperature but with a concomitant improvement in elongation and reduction in are a. No change in macroscopic fracture mode was observed with sample ori entation. Fracture, on a microscopic scale, was predominantly ductile comprising microvoid nucleation, growth and coalescence. The tensile d eformation and fracture process are discussed in the light of the comp eting influences of intrinsic microstructural effects, matrix deformat ion characteristics, test temperature and grain-boundary failure.