Observation of the Coupling Current During Stress Corrosion Cracking of Aluminum Alloy 5083

Abstract

A unique fracture mechanics device was created to allow for simultaneously measuring the load and localized electrochemical potential gradients in AA5083 bend bars. For the first time, periodic Scanning Vibrating Probe (SVP) maps were collected in order to obtain a full view of the coupling current, (which can be deduced from measured potential gradients) that emanates from an anodic crack tip. As a result of mapping the current density over a wide surface area compared to the area of the notch and crack tip, clarification is given on whether or not the external surfaces of an alloy or any other metal that experiences Stress Corrosion Cracking (SCC) play a role in crack growth. The SVP maps clearly show the anodic and cathodic potential gradients of a growing crack (resulting from SCC) in an AA5083 fracture mechanics specimen while the stress intensity increases. The notch and crack-tip remained anodic throughout most of the obtained scans for sensitized and as-received specimens. Furthermore, a coupling effect is observed on sensitized specimens even at low fracture toughness values in sensitized specimens under load for longer periods of time (> 1 week). These higher resolution maps captured during the crack growth process give more insight to the SCC phenomenon and the electrochemical mechanisms of crack growth in AA5083 and other alloys.