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Analysis and Application of Treatments to Mitigate Exfoliation Corrosion (Delamination) of 5XXX Series Aluminum



OBJECTIVE: Research and develop chemical or non-chemical methods and processes to impart surface morphology modifications to aluminum-magnesium (Al-Mg) alloys to mitigate and increase the exfoliation corrosion resistance. 

DESCRIPTION: 5000-series marine grade aluminum alloys are used in high-speed, high-performance ships and marine craft due to the many positive attributes (high strength-to-weight ratio, weld-ability, and marine corrosion resistance) of those alloys. Initial research in aluminum alloys for marine use indicated that certain alloys and tempers could be made resistant to exfoliation corrosion. Testing of these alloys and tempers was conducted for two years prior to acceptance of those alloys and tempers for widespread use in the U.S. Navy. Most of the Navy platforms, however, have service lives of 20-30 years and have subsequently exhibited exfoliation corrosion. Exfoliation is a special type of inter-granular corrosion that occurs on the elongated grain boundaries. The corrosion product that forms has a greater volume than the volume of the parent metal. The increased volume forces the layers apart, and causes the metal to exfoliate or delaminate. Innovative approaches for processes that protect against exfoliation are needed. Currently, when exfoliation corrosion occurs, the Navy must remove and replace the affected plate, resulting in costly and time-consuming maintenance actions. Prevention of exfoliation corrosion would produce lifecycle cost savings and increase the operational availability of ships and craft using 5000-series aluminum. The small business must research and develop applicable technologies that can mitigate and prevent exfoliation from occurring over the expected 25-year service life of a ship or craft. The proposed technology must improve the exfoliation resistance by 50% without reducing the strength in the material or inducing pitting or other deleterious changes to the material microstructure. The small business will identify the gaps between potentially applicable technologies and the future requirements and discuss the research and development (R&D) and innovation needed to fill the gaps thus justifying the need for the R&D or innovation. The proposed treatment must maintain paint adhesion and mechanical bonding durability of the Al-Mg alloy. The goal of this effort is to prevent exfoliation corrosion from occurring over the expected 25-year service life of a ship or craft. Technologies currently used to mitigate and improve the corrosion resistance of titanium, steel, stainless steel, and nickel-based alloys may be applicable. Various technologies currently being utilized by the aerospace, nuclear, and oil industries to address issues related to exfoliation, stress corrosion cracking, fretting, and wear have shown to be effective. 

PHASE I: Research and develop applicable technologies that meet the overall objective of the proposal with a focus on development, testing, and analysis of the selected technology. The proposed research should include developing an understanding of the physical mechanisms to improve the exfoliation corrosion by altering the surface structure and morphology of the aluminum. Phase I should include technology development, required testing, technical rationale for the testing, analysis, project goals, milestones, and deliverables. Address any hazardous material and environmental issues. The Phase I Option, if awarded, will include the initial treatment specifications and capabilities description to prototype the proposed solution in Phase II. Develop a Phase II plan. 

PHASE II: Based on the results of Phase I and the Phase II Statement of Work (SOW), treat sample coupons and conduct short-term testing of those coupons. Take measurements at each test point to determine if actual exfoliation or grain boundary formation occurs as predicted. Coupon testing must occur at an ISO 9001:2015 certified facility. The developed technology must be demonstrated on 5XXX aluminum. Samples must be treated, tested, and evaluated for exfoliation corrosion. Corrosion testing must be conducted at an ISO 9001:2015 certified facility. Evaluation of test samples must include on-site monitoring to determine if any corrosion occurs during testing. Test samples must also be inspected and evaluated to determine if the treatment adversely affects material and metallurgical properties. Test samples must be evaluated to assess the paint adhesion and mechanical bonding durability of the technology. The Phase II test results must be used to optimize the technology for a production environment. Develop a Phase III plan for technology transition to the Navy. 

PHASE III: Support the Navy in transitioning the technology to Navy use. Identify all hardware, and develop all use documentation necessary to implement the technology at manufacturing facilities. The proposed technology is applicable to ship classes including the Littoral Combat Ship (LCS), Ship to Shore Connector (SSC), and Ticonderoga-class (CG-47). Civilian applications in the marine and oil servicing industries are possible. The proposal surface technology has the potential for commercial applications in the aerospace, nuclear, and oil industries. Various surface treatment technologies have been developed and used to address issues with exfoliation, stress corrosion crack, fretting, and wear in titanium, steel stainless steel, and nickel-based alloys. 


1: Brosi, J.K., et al. "Delamination of Sensitized Al-Mg Alloy During Fatigue Crack Growth in Room Temperature Air." Metallurgical and Materials Transactions A, Vol. 34A, November 2012, 3952-3956.

2:  Mohsen, S. et al. "Grain Orientation Effects on Delamination During Fatigue of a Sensitized Al-Mg Alloy." Philosophical Magazine Letters, Vol 95, Issue 11, Nov 2015, 526-533.

3:  Liao, M. et al. "Effects of Ultrasonic Impact Treatment on Fatigue Behavior of Naturally Exfoliated Aluminum Alloys." International Journal of Fatigue, 30 (2008), 717-726.

KEYWORDS: Exfoliation Corrosion Of Aluminum; Corrosion Resistant Surface Treatments; Preventing Exfoliation Corrosion; Corrosion Of Marine Grade Aluminum Alloys; Corrosion Failure Mechanisms For 5000-series Aluminum; Service Life Limiting Factors For 5000-series Aluminum 


Michael Pyryt 

(215) 897-1948 

William Schoenster 

(202) 781-2618 

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