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51317--9575-Intergranular Corrosion in Al-Mg 5XXX Alloys Under Atmospheric Exposures

Picture for Intergranular Corrosion in Al-Mg 5XXX Alloys Under Atmospheric Exposures
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Critical factors affecting intergranular corrosion in AA5XXX under atmospheric exposures. Cathodic kinetics play an important role in atmospheric or open circuit localized corrosion.  Electrochemical experiments in thin film electrolytes were conducted to explain the corrosion morphology observed in lab exposures.

 

Product Number: 51317--9575-SG
ISBN: 9575 2017 CP
Author: Piyush Khullar
Publication Date: 2017
Industry: Science of Corrosion
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Al-Mg 5XXX alloys are widely used for marine applications due to their low cost high strength-to-weight ratio and good weldability. Alloys containing more than 3 wt% Mg when exposed to standard service temperatures for extended periods of time can become sensitized and susceptible to localized corrosion; particularly intergranular corrosion (IGC). Many studies have investigated this IGC phenomenon in AA5XXX and attribute it to precipitation of a more anodic ?-phase (Al3Mg2) along grain boundaries after exposure to hot environments during service.Previous studies have investigated the role of metallurgical and electrochemical factors on IGC and indicate that degree of sensitization (DoS) orientation and time of exposure have a strong influence on grain boundary precipitation of ?-phase and hence IGC in AA5XXX. The majority of IGC studies have been conducted in full immersion while much of the marine infrastructure is exposed to atmospheric conditions. There is a need to extend the full immersion corrosion framework and conduct IGC studies under atmospheric and/or thin film conditions.This study aims to develop a quantitative understanding of critical factors affecting IGC in AA5XXX under atmospheric exposures. The present work shows that cathodic kinetics play an important role in atmospheric or open circuit localized corrosion. Preliminary results have shown that strong oxidizers like ozone (O3) and persulfate (S2O8-) salt loading density solution resistance solution thickness cathode area and type of cathode have a strong influence on IGC in thin films. A novel experimental set-up has also been developed to conduct electrochemical experiments in thin film electrolytes to explain the corrosion morphology observed in lab exposures. Initial thin film electrochemical results agree well with the existing corrosion framework for IGC in full immersion. An understanding of IGC in thin films/atmospheric exposures will provide a basis for developing a framework for IGC in thin films and comparing it to existing corrosion framework for IGC in full immersion.

Key words: atmospheric corrosion, intergranular corrosion, thin films electrolyte, oxidizer

Al-Mg 5XXX alloys are widely used for marine applications due to their low cost high strength-to-weight ratio and good weldability. Alloys containing more than 3 wt% Mg when exposed to standard service temperatures for extended periods of time can become sensitized and susceptible to localized corrosion; particularly intergranular corrosion (IGC). Many studies have investigated this IGC phenomenon in AA5XXX and attribute it to precipitation of a more anodic ?-phase (Al3Mg2) along grain boundaries after exposure to hot environments during service.Previous studies have investigated the role of metallurgical and electrochemical factors on IGC and indicate that degree of sensitization (DoS) orientation and time of exposure have a strong influence on grain boundary precipitation of ?-phase and hence IGC in AA5XXX. The majority of IGC studies have been conducted in full immersion while much of the marine infrastructure is exposed to atmospheric conditions. There is a need to extend the full immersion corrosion framework and conduct IGC studies under atmospheric and/or thin film conditions.This study aims to develop a quantitative understanding of critical factors affecting IGC in AA5XXX under atmospheric exposures. The present work shows that cathodic kinetics play an important role in atmospheric or open circuit localized corrosion. Preliminary results have shown that strong oxidizers like ozone (O3) and persulfate (S2O8-) salt loading density solution resistance solution thickness cathode area and type of cathode have a strong influence on IGC in thin films. A novel experimental set-up has also been developed to conduct electrochemical experiments in thin film electrolytes to explain the corrosion morphology observed in lab exposures. Initial thin film electrochemical results agree well with the existing corrosion framework for IGC in full immersion. An understanding of IGC in thin films/atmospheric exposures will provide a basis for developing a framework for IGC in thin films and comparing it to existing corrosion framework for IGC in full immersion.

Key words: atmospheric corrosion, intergranular corrosion, thin films electrolyte, oxidizer

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