Strain rate dependence of flow and fracture behavior for a rapidly-solidified Al alloy

Abstract

Serrated flow, also known as Portevin-Le Chatelier (PLC) effect, has been studied extensively in engineering metals, especially in conventionally solidified aluminum alloys. In most cases, the phenomenon has been recognized to associate with the dynamic strain aging (DSA) process in micromechanism, and its occurrence has been documented to depend on temperature, strain level, and strain rate. It is often accompanied by the formation of a definite pattern of deformation band (the PLC band) on the specimen surface. For the strain rate dependence in particular, a negative strain rate sensitivity of flow stress has been verified to be a necessity for the serrated flow, not only by theoretical deduction, but also from experimental results. It is worthwhile to note that, in certain cases, the alloy undergoing the serrated flow fails by a shear fracture mode and therefore the shear fracture has been considered to be a direct result of DSA. This connection seems plausible in view of the fact that the negative strain rate sensitivity has also been found to associate with the shearing process and that the shear fracture is also thought to be a result of unstable flow localization. For the aluminum alloys with rapid solidification, little has beenmore » known on both serrated flow and shear fracture. In a previous study, the shear fracture mode has been investigated for a rapidly solidified aluminum scrap alloy. This alloy has also exhibited serrated flow behavior under certain conditions. For the present work, the strain rate dependence of the plastic flow characteristics and the fracture mode variation in the alloy will be studied with emphasis on the rate response of the serrated flow and the shear fracture and some correlation between the two phenomena.« less