THE ROLE OF STRESS IN THE CORROSION CRACKING OF ALUMINUM ALLOYS

Abstract

This work examines the effect of stress on the rate of sensitization, the rate of pitting corrosion and the rate of crack nucleation of aluminum alloy 5083-H116 aluminum. Stress corrosion cracking in aluminum superstructures of Naval vessels is a multibillion-dollar maintenance problem, which requires more scientific understanding to better predict and mitigate. To investigate the role of applied stress on these corrosion-related processes, rolled plate of AA5083 was placed under tensile stress through bending while being subject to elevated temperature and salt spray. Nitric acid mass loss tests quantified the amount of sensitization as a function of stress level. Optical micrographs were used to determine the rate of pitting corrosion and crack nucleation while under applied tensile stress. The effect of applied, elastic stress on the degree of sensitization was inconclusive. Applied stress did increase the rate of localized corrosion, in terms of both pitting and intergranular corrosion. Moreover, the orientation of the plate with respect to the applied tensile stress, strongly affected the type and amount of localized corrosion observed. When the tensile stress was applied across the rolling direction, more localized corrosion occurred and intergranular corrosion dominant over pitting.