Environmentally assisted fatigue behaviour of stress relieved metal inert gas (MIG) AA5083 welds in 3.5% NaCl solution

Abstract

Environmentally assisted fatigue crack propagation behaviour of metal inert gas (MIG) welded AA5083 joints under stress relieving treatment has been investigated. In this study, ‘in-process’ stress relieving treatment, namely static thermal tensioning was applied during MIG welding process. Subsequently, fatigue crack propagation tests were performed in 3.5% NaCl solutions with and without a chromate inhibitor. A sinusoidal loading wave form was used in these fatigue tests with stress ratio, R and frequency, f of 0.1 and 8Hz respectively. For complementary tests, residual stress measurements were conducted using neutron diffraction method whereas effect of corrosive environments was assessed using potentiodynamic polarisation technique. Results showed that electrochemical corrosion characteristics of the weld metals under stress relieving treatment were improved marked by the presence of anodic passivation regions in potentiodynamic polarisation curves with reduced corrosion rates. Moreover, synergistic effect of compressive residual stress and repassivation of the weld joints seemed to inhibit environment fatigue crack propagation.