The influence of precipitate morphology on microvoid growth and coalescence in tensile fractures

Abstract

A study of the fine-scale topography of tensile fractures in selected aluminum alloys was made to provide information on the influence of second-phase microconstituents on microvoid initiation, growth, and coalescence. The test materials included three commercial aluminum alloys and three high-purity Al-Cu binary alloys heat-treated to provide a wide range of precipitate morphology. The fracture surfaces of notched-tensile specimens were examined, and the fine-scale topographic features compared with microstructural parameters. The principal observations made were: 1) for a dual precipitate morphology, void initiation first occurs at the larger precipitates, 2) fracture may occur by growth and coalescence of voids initiated at only a small fraction of precipitate sites, 3) void initiation can occur independent of precipitate particles, and 4) intergranular fracture may occur by growth and coalescence of microvoids within the grain-boundary zone. These observations established that the detailed aspects of fracture by microvoid coalescence are intimately related to precipitate morphology, but no simple, uniform correlation of fracture surface topography with precipitate size and distribution was evident.