Unloading Effects in Aluminium-Zinc Single Crystals

Abstract

DURING interruptions of tensile tests on crystals of pure metals, unloading has been shown to produce yield points on subsequent retesting^1–3. A similar procedure with alloy specimens causes strain-ageing yield points to be reduced⁴. Unloading yield points are first observed during the stage 2 hardening region of the stress-strain curve and their magnitude increases with stress. At high stresses, strain-ageing yield points can be observed to disappear completely as a result of unloading. Work in these Laboratories using single crystals of dilute aluminium-zinc alloys contrasts both types of yield point and indicates that dynamic recovery which occurs under the action of the applied stress at room temperature is suppressed as a result of unloading. This work forms part of a study of the general effect of unloading during interruptions of tensile tests on single crystals of aluminium and of dilute aluminium alloys.