Non Chromated Coating Systems For Corrosion Protection Of Aircraft Aluminum Alloys Preprint
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Non Chromated Coating Systems For Corrosion Protection Of Aircraft Aluminum Alloys Preprint
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Author :
language : en
Publisher:
Release Date : 2006
Non Chromated Coating Systems For Corrosion Protection Of Aircraft Aluminum Alloys Preprint written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with categories.
The Air Force requires the development of an environmentally compliant chromate-free aircraft coating system that meets or exceeds current corrosion protection capabilities. A number of non-chromated pretreatments and primers have been independently developed over the past years. This report compares the corrosion resistance performance of selected fully non-chromate systems to the standard chromate containing coating system. The data identified two non-chromated systems that performed comparably to the standard chromated aircraft coating system.
Environmentally Compliant Coatings Using Non Chromated Systems
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Author :
language : en
Publisher:
Release Date : 2001
Environmentally Compliant Coatings Using Non Chromated Systems written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2001 with categories.
Conversion coatings and primers used for the corrosion protection of aluminum alloy components in aircraft are based, almost exclusively, on chromate systems that are on the Environmental Protection Agency List of hazardous materials. Chromium is targeted for elimination from the workplace. This effort is part of a research program to develop a suitable replacement for chrome in coatings technology. This effort focused on the use of cerium chemistry to provide the corrosion inhibition for aluminum alloys used in the aircraft industry. The primary tasks were the development of a non-chromated conversion coating and surface treatment and a non-chromated primer coating system for military aircraft. This report presents the development, characterization, and evaluation of inorganic coatings that can serve as potential replacements for current chromate coatings. This effort was performed by the Materials Research Center at the University of Missouri-Rolla and the Boeing Corporation.
Anti Corrosion Properties Of A Non Chromate Conversion Coating For Aerospace Aluminum Alloys
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Author : Shruthi Tiruchirapalli Kumar Raj
language : en
Publisher:
Release Date : 2020
Anti Corrosion Properties Of A Non Chromate Conversion Coating For Aerospace Aluminum Alloys written by Shruthi Tiruchirapalli Kumar Raj and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020 with Electronic dissertations categories.
The aerospace industry uses a variety of metal alloys as structural components in aircraft. Corrosion and degradation of these metals in service is typically inhibited using a multi-layer coating system (conversion coating + primer + topcoat). Historically used conversion coatings and primers contain Cr(VI) as the active corrosion inhibitor. Due to human health and environmental concerns, there is a world-wide effort to eliminate chromate from use and to replace these coatings with more environment-friendly and equally-as-effective coatings. The trivalent chromium process (TCP) conversion coating is the leading replacement candidate. A challenge with implementing this conversion coating for protecting high Cu aluminum alloys is that it is not as good as the legacy chromate coatings for reasons that remain poorly understood. In this dissertation project, fundamental research was conducted to better understand how to improve the anti-corrosion properties of TCP on AA2024-T3, a high Cu containing aerospace alloy. A focus was on understanding system-level interactions between the coating and alloy surface, and how it correlates with early-stage failure of alloys. The overall objective of this dissertation project was to improve the corrosion performance of TCP conversion coatings through: (i) process parameter optimization; (ii) a better understanding of early-stage failure mechanisms, specifically, the sites where alloy corrosion initiates and the coating composition and structure on and around these sites. The final chapters of this dissertation also focus on the use of TCP as a sealant for surface modified (anodized) AA2024-T3 and comparing the effectiveness of a TCP seal against other industrially used sealing methods.
Investigation Of The Anti Corrosion Properties Of Trivalent Chromium Process Coatings On Various Surface Pretreatments Of Aerospace Aluminum Alloys
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Author : Sarah McFall-Boegeman
language : en
Publisher:
Release Date : 2021
Investigation Of The Anti Corrosion Properties Of Trivalent Chromium Process Coatings On Various Surface Pretreatments Of Aerospace Aluminum Alloys written by Sarah McFall-Boegeman and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2021 with Electronic dissertations categories.
The aerospace industry uses a variety of metals and alloys, primarily aluminum alloys, for the different structural components in aircraft including the fuselage, landing gear, tail fins, and the many other parts. As these components are metal based, the control and mitigation of corrosion in service is of paramount importance. The military and civilian aviation sectors spend considerable sums of money annually on corrosion prevention and maintenance. Components made with aluminum alloys are generally placed in service with a multilayer coating system to prevent corrosion. This coating system consist of a conversion coating, primer, and topcoat. The coating system can inhibit corrosion in multiple ways, but the general mechanism involves barrier layer protection that reduces contact of the environment with the underlying metal. Legacy conversion coatings and primers have chromate (Cr(VI)) as a component. While chromate is an excellent corrosion inhibitor, it is toxic and constitute a significant environmental hazard. There is a current technological need to (i) replace chromate conversion coatings and primers with nonchromateor zero-chrome coating systems and (ii) understand how to properly pretreat the aluminum alloys surfaces for application of such surface finishes. The trivalent chromium process (TCP) coating is the leading replacement non-chromate conversion coating and praseodymium and new aluminum-based coatings are replacement primers being investigated. There is also a scientific need to better understand how to properly pretreat aluminum alloys in order to properly form conversion coatings and primers that effectively prevent environmental degradation and corrosion. These surface pretreatments typically include abrasion and polishing, wet chemical cleaning, and deoxidation or desmutting.In this dissertation project, fundamental research was conducted to better understand how surface pretreatments of aluminum alloys impact the formation of TCP conversion coatings and the mechanisms by which TCP conversion coatings inhibit electrochemical corrosion in laboratory measurements and during accelerated degradation testing. Research was also conducted to learn how effectively TCP coatings can seal porous anodic oxide coatings on aluminum alloys thereby improving the barrier properties and electrochemical corrosion resistance. The specific surface pretreatments investigated included laser cleaning and hyperpassivation of aluminum alloyAA2024-T3, in comparison with conventional wet chemical processing. Additionally, studies were performed to learn the mechanisms and effectiveness of TCP sealants for anodic coatings formed on this aluminum alloy during sulfuric acid (SA) and sulfuric acid/boric acid (SABA)anodization.
Corrosion Protection Of Aluminum Alloys Used In Aircraft Testing Analysis And Development Of Environmentally Compliant Coatings And Pretreatments For The Corrosion Protection Of Aircraft Alloys
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Author :
language : en
Publisher:
Release Date : 2002
Corrosion Protection Of Aluminum Alloys Used In Aircraft Testing Analysis And Development Of Environmentally Compliant Coatings And Pretreatments For The Corrosion Protection Of Aircraft Alloys written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2002 with categories.
This report describes the work for FY 2000 for the Project Corrosion Protection of Aluminum Alloys Used in Aircraft (Grant # F49620-99-1.0283) for AFOSR. This Report contains the following sections that address the technical goals of the project: Goal 1. Improved electrochemical test methods and protocols for characterizing the performance of coated aircraft alloys. Goal 2. Surface Analysis Studies of Degradation of Coatings Properties Goal 3. SVET Studies of Coated Aluminum Alloys Goal 4. Advanced Spectroscopy of Coating/Metal Systems Goal 5. Further examination of conductive polymers for chrome free metal pretreatment primers for Al alloys Goal 6. Development of molecular probes for examining changes in thin coating films during exposure Goal 7. Electrochemical Instrumentation Development Goal 8. Chrome-free pretreatment materials based on sol-gel optimization - new silicon oligomer design & synthesis Goal 9. Improved design/expert systems methods for total aircraft coatings systems design (with AFRL/WPAFB).
Measurement And Modeling Of Corrosion Degradation Of Coated Aluminum Alloy 7075 T6
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Author : Mahdi Jokar
language : en
Publisher:
Release Date : 2022
Measurement And Modeling Of Corrosion Degradation Of Coated Aluminum Alloy 7075 T6 written by Mahdi Jokar and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2022 with Aluminum coating categories.
Aluminum alloys are commonly used in many structural applications, including Navy aircraft, due to their low density, high strength, and general corrosion resistance. However, these alloys can be susceptible to localized corrosion: pitting, crevice corrosion, intergranular corrosion, etc. Relatively noble fasteners are often used to join the aluminum alloys panels in Navy aircraft and localized corrosion of Al is greatly accelerated due to galvanic coupling when coupled with more-noble metal fasteners. Also, the galvanic interaction between aluminum alloy and noble fastener is a source of great expense for the maintenance of Navy aircraft. Therefore, there is a need to predict the galvanic corrosion behavior of coated high strength Al alloys. The aim of this project is to develop predictive models describing the effects of environmental factors and time as well as coating systems based on machine learning prediction methods. Such relations could potentially be applied to guide future aircraft design and predict lifetimes and required service intervals for deployed resources. In the first part of this project, data were collected to expand the dataset for modeling. Accelerated tested using impressed current between a fastener and panel was used instead of simple galvanic coupling, which had been used in previous studies. The motivation is to have more control over the corrosion acceleration process. Two coating systems, including a chromate-containing and a non-chromated coating system, were exposed to ASTM B117 and cyclic salt spray exposure environments. The coatings were scribed prior to exposure to further accelerate the corrosion rate. The nature of attack depended on the magnitude of the applied impressed current and the exposure environment for the chromate-free adhesion promoting surface pretreatment. However, the nature of the attack did not depend upon the magnitude of applied current for the chromated pretreatment system, indicating that using impressed current is suitable for the acceleration of corrosion in chromated systems. The response of the current during drying and rewetting also varied depending on the coating system. In the second part of the study, different amounts of impressed currents were used between the fastener and aluminum alloy panel to accelerate and simulate the galvanic corrosion and generate more data to develop predictive models. Twelve coating systems including CCC, adhesion promoter and TCP as pretreatment, praseodymium-rich and chromated as primer coating with and without polyurethane as topcoat were exposed to ASTM G85-Annex 2. Also, the effect of environmental factors was evaluated by using different chloride concentration and relative humidity for the exposure environment. Electrochemical measurements, optical profilometry and photography were used to characterize and measure the corrosion performance of different coating systems. The attack morphology depends on the coating system and environmental conditions, but not the applied current. The amount of passed charge was almost equal for different coating systems and it was controlled by the galvanostat and environmental conditions. The attack morphology for Pr-rich primer samples was delamination at the scribe region and far from it. However, for the chromated primer panels the attack was metal dissolution and partially coating peel off only at the scribed region. Electrochemical impedance spectrometry was used to compare the corrosion resistance and porosity of different coating systems. In the last section of study, damage functions for galvanic corrosion prediction were developed using artificial neural networks (ANN), random forest regression (RFR), and multiple linear regression (MLR) approaches. The effects of different independent factors including pretreatment, primer coating, topcoat, relative humidity, chloride concentration, fastener material, fastener quantity, existence of defect, environment, and time of wetness were quantified against galvanic coupling lost volume. ANN, RFR and MLR all showed a reasonable fit of lost volume as a function of different inputs.
Environmentally Friendly Rare Earth Based Inhibitors In Conversion Coatings And Paint For The Corrosion Protection Of Aluminum Alloys
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Author : Scott A. Hayes
language : en
Publisher:
Release Date : 2005
Environmentally Friendly Rare Earth Based Inhibitors In Conversion Coatings And Paint For The Corrosion Protection Of Aluminum Alloys written by Scott A. Hayes and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2005 with Aluminum alloys categories.
"Aluminum alloys such as 7075-T6 and 2024-T3 are commonly used in aircraft because of their strength to weight ratio. While the mechanical properties of these alloys are very good, they are particularly susceptible to corrosion. Coatings are commonly used to protect these aluminum alloys to corrosive attack. One type of coating, called a conversion coating, is a thin, inorganic film normally deposited directly on the bare metal surface. The other types of coatings, generically referred to as paints, include primers which are applied over a conversion coating. A primer consists of a binder, usually organic, and pigments, which are mostly inorganic particles dispersed in the binder. Part of the primer's pigment content includes compounds that can provide corrosion protection. For the corrosion protection of aluminum, the most commonly used conversion coating and primer pigments contain Cr(VI) compounds. While highly effective, Cr(Vl) compounds are becoming undesirable due to their increasingly recognized toxicity and the greatly increased handling costs due to the health threat that they pose. For these reasons, much research has been conducted in recent years to find alternatives to chromates. The central purpose of the thesis work presented herein was to develop non-chromated conversion coatings and primers. To support this effort, the fundamental chemistry of cerium, a potential chromium replacement, was studied. Also undertaken was the development of a methodology for using the scanning vibrating electrode technique (SVET) to characterize pretreatments and coatings. As a consequence of this study, five patent applications were filed as well as numerous papers and reports"--Abstract, leaf iv.
Magnesium Rich Primer For Chrome Free Protection Of Aluminum Alloys Preprint
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Author :
language : en
Publisher:
Release Date : 2007
Magnesium Rich Primer For Chrome Free Protection Of Aluminum Alloys Preprint written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2007 with categories.
Hexavalent chromium compounds used for corrosion protection are one of the top hazardous waste materials generated by the U.S. Air Force and legislation is in effect to further restrict their use. Magnesium rich primers that utilize sacrificial magnesium metal pigment to cathodically protect aerospace aluminum alloy substrates are a potential alternative to chromated primers. This material has proven to be particularly effective as part of a completely chromate-free coating system in which a non film forming surface treatment and an Advanced Performance Coating (APC) grade topcoat are utilized. Samples using the latest advanced formulations show excellent corrosion protection of scribed AA2024-T3 panels in both ASTM B 177 and outdoor exposure at Dayton Beach, FL. Despite initial concerns regarding the reactivity of the magnesium metal pigment being used, the flammability and handling characteristics have not shown any potential problems to date. Transitioning a new class of corrosion protective primer coating such as this requires more testing than normal. The current Air Force plan involves qualification to a "system level" coating specification, MIL-PRF-32239. In addition, simulated lap joints with various fasteners specific to the target aircraft will be evaluated, along with compatibility on alternative substrates and evaluation of coating reparability characteristics.
Environmentally Compliant Novolac Superprimers For Corrosion Protection Of Aluminum Alloys
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Author :
language : en
Publisher:
Release Date : 2006
Environmentally Compliant Novolac Superprimers For Corrosion Protection Of Aluminum Alloys written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with categories.
The Environmental Protection Agency (EPA) in the US has imposed legislations on the use of hexavalent chromium and solvents contributing to emission of volatile organic compounds in primer coatings. This has led researchers to pursue development of alternative environmentally-friendly coatings which would eliminate chromate conversion coatings (CCC). This thesis discusses the work done towards the development of a novel, chromate-free, low-VOC, water-based, organic coating system for corrosion protection of AA 2024-T3 aerospace alloy. These special coatings which can be applied directly to the metal are termed as 'superprimers' and consist of novolac epoxy binder, silanes, polyurethane and non-chromate inhibitors. Coating evaluation tests were employed to compare the performance of the superprimer coatings with controls. SEM, FTIR and NMR were carried out to understand the chemistry of the coatings. The requirement for a conversion coating was obviated and the coating system developed was on par with the chromate-based control coating in terms of performance.
Environmentally Compliant Corrosion Resistant Electrically Conductive Inorganic Coatings For Aluminum Alloys
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Author :
language : en
Publisher:
Release Date : 2001
Environmentally Compliant Corrosion Resistant Electrically Conductive Inorganic Coatings For Aluminum Alloys written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2001 with categories.
The objective of this project was to develop an environmentally compliant conversion coating for use on aerospace aluminum alloys (e.g., AA2024-T3). This conversion coating was to replace the current chromate conversion coating processes in both mode of application (bath or spray applied in the depot) and function (stand alone corrosion protection, adhesion to organic layers, self-healing, and low electrical contact resistance). Hydrotalcite (HT) was developed within this program as a replacement to chromate conversion coatings. HT coatings are formed by exposure of aluminum and its alloys to alkaline lithium salt solutions. The coating chemistry used to form these conversion coatings has many processing variables (e.g., time, temperature, anion, etc.). A Fractional Factorial Design was used to determine that temperature was one the more critical processing variables. The FFD study also determined that HT coatings formed from nitrate-based chemistries had consistently better stand-alone corrosion protection properties. Through the use of additional oxidants within the coating bath, HT coatings with the ability to withstand 168 hours of salt spray could be formed in less than 6 min. HT conversion coatings could also be post-treated (e.g., hydrothermally aged, surfactant) to revert the hydrotalcite to aluminum oxide, or augmented to include high valence-state rare earth cations (e.g., cerium). Hydrothermal aging allowed a procedure to chemically anodize aluminum, while incorporation of cerium into the molecular gallery of the hydrotalcite structure provided a means to develop self-healing characteristics, a highly sought property characteristic of chromate-based coatings. Self- healing was indeed demonstrated by the cerium doped HT coatings. The adhesion of epoxy coatings to the hydrotalcite coating was studied in detail. The Lewis-base nature of HTs makes them intrinsically less able to be wet by the Lewis- base nature of epoxy.