Adiabatic shear localization and erosion of strong aluminum alloys

A high strength aluminum alloy, 7075-T651, was eroded by ball-bearing impact at high velocities (about 180 m s t̄1) at normal and oblique incidence. Scanning electron microscope studies of the target and ejected chip show that the fracture surface is covered with myriad small globules (roughly 1 μm in dimension) whose form was clearly established by the effect of surface tension on a fluid metal. It is argued that for high strength age-hardened alloys like this, chips are formed by fracture across molten adiabatic shear bands which then quickly solidify after separation to give the globular surface. Such structures were not found on eroded surfaces of the much softer commercially pure aluminum.