The effect of applied tensile stress on localized corrosion in sensitized AA5083

Abstract

This thesis describes significant changes in the type and degree of localized corrosion for sensitized AA5083 under an applied tensile stress. AA5083 is an aluminum-magnesium alloy that experiences severe intergranular corrosion and intergranular stress corrosion cracking if sensitized. In this research, AA5083-H116 plates were cut into bend-bar samples along both the rolling and transverse directions, and then sensitized to two different levels using laboratory heat treatments of 7 and 30 days at 100°C. The sensitized samples were subjected to elastic tensile loading using a 4-point bend rig while being exposed to a 0.6 molar saltwater solution. Electrochemical polarization was performed on the tensile regions of the samples while under applied stress. Potentiodynamic scans showed that although sensitization causes the most change in electrochemistry, stress does shift the Tafel plot to be more stable when comparing the values for open circuit potential, but reduces the pitting potential of the passivating oxides. Confocal microscopy showed that samples with applied tensile stress produced a much higher density of localized corrosion, including pitting and intergranular corrosion than samples without applied tensile stress. The degree of corrosion damage was slightly higher for samples loaded in the transverse direction compared to samples loaded in the longitudinal direction.