What is it about?
In the magnesium supersaturated aluminum alloy AA5456-H116, this work demonstrates how environmental cracking can be best mitigated in a wide spectrum of corrosive oceanic environments. Electrochemical characterization of pitting and stable zones for the aluminum matrix and the easily dissolved beta phase demonstrate that the rate at which this accelerated fracture occurs is dependent on the electrochemical state of stability locally experienced by these phases at the crack tip, which can be at least partially controlled both experimentally and in service.
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Why is it important?
The efficacy of electrochemical potential control in mitigating intergranular stress corrosion cracking demonstrates a need for further research into metal-rich coatings for marine vehicles. These coatings, if designed properly, could offer an economic solution to mitigate environmental cracking on bulk ship structures by controlling potentials present at the alloy surface by galvanic coupling and chemical effects.
Perspectives
This work is quite interesting due to the range of saline environments covered, which show effects of pH, solution viscosity, and chloride content on the ability to either partially or fully mitigate IG-SCC. It turns out that ohmic drop effects are likely halting IG-SCC from being completely shut off in certain environments due to shifting in the pitting potentials controlling the susceptibility, which agrees with crack tip potential modeling done previously. Surprisingly, some of the trends noticed here mirror those seen in environmental fracture of steels, which have vastly different chemistries, corrosion products, and mechanical properties.
Matthew E. McMahon
University of Virginia
Read the Original
This page is a summary of: Mitigation of Intergranular Stress Corrosion Cracking in Al–Mg by Electrochemical Potential Control, JOM, April 2017, Springer Science + Business Media,
DOI: 10.1007/s11837-017-2362-2.
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