Mechanics of fracture in hot rolled Al-7Mg alloy prepared from rapidly solidified powder

Abstract

Al-7Mg rapidly solidified powders were processed by extrusion to prepare billets for rolling. The billets were rolled at temperatures between 300 and 500°C and tested in tension. The fracture surfaces were examined and this paper illustrates that in the absence of larger precipitates the fracture mechanism is dependent upon the oxide content and morphology inherent in the air atomized powders. When larger particles are present (1–3 μm), the fracture is initiated and propagated by the particles; the oxide does not feature in the fracture process. Some billets were rolled in multi passes and it is shown that a maximum of about 40% reduction may be obtained before the oxide particles cause exfoliation by fracture at prior particle boundaries. It is concluded that the thermomechanical process route for the production of engineering materials must pay particular attention to the distribution of the oxide film and to maintaining the thermal stablhty of the atomized powders.