Pitting and Stress Corrosion Cracking Susceptibility of Nanostructured Al-Mg Alloys in Natural and Artificial Environments |
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Authors: | Mala M Sharma Constance W Ziemian |
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Affiliation: | (1) Department of Mechanical Engineering, Bucknell University, Dana Building, Lewisburg, PA 17837, USA |
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Abstract: | The stress corrosion cracking (SCC) behavior of two developmental nanocrystalline 5083 alloys with varied composition and
processing conditions was studied. The results were compared to a commercial aluminum AA 5083 (H111) alloy. The pitting densities,
size and depths, and residual tensile strengths were measured after alternate immersion in artificial seawater and atmospheric
exposure under different loading conditions. Optical and scanning electron microscopy (SEM) with EDX was used to analyze the
fracture surfaces of failed specimen after removal at selected intervals and tensile testing. One of the nanostructured Al-Mg
alloys exhibited significantly superior pitting resistance when compared to conventional microstructured AA 5083. Under conditions
where pitting corrosion showed up as local tunnels toward phase inclusions, transgranular cracking was observed, whereas under
conditions when pitting corrosion evolved along grain boundaries, intergranular cracking inside the pit was observed. Pit
initiation resistance of the nano alloys appears to be better than that of the conventional alloys. However, long-term pit
propagation is a concern and warrants further study. The objective of this investigation was to obtain information regarding
the role that ultra-fine microstructures play in their degradation in marine environments and to provide insight into the
corrosion mechanisms and damage processes of these alloys. |
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Keywords: | aluminum corrosion testing failure analysis mechanical testing |
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