Final Report Summary - COMAG (Development and Implementation of Conductive coating for Magnesium sheets in A/C)
Executive Summary:
The main objective of this project was development and implementation of high corrosion resistance conductive coating for magnesium sheets in A/C. This coating should provide minimal bare corrosion requirement for stand-alone conductive coating – cycling salt spray test in accordance with EUROCAE ED14/ RTCA DO160 Section 14 - 48 hours in SST, 48 hours out of SST without rinse. This coating should provide corrosion resistance for electrical bonding scheme - small area of conductive coating on sheet with selective coating – 168 hours in SST (ASTM 117 and MIL-DTL-5541 Class 3). The coating won't influence strength and fatigue parameters of the substrate - high-strength magnesium sheet.
Project Context and Objectives:
CoMag project deals with development and implementation of high corrosion resistance conductive coating for magnesium sheets in A/C.
The development was based on very thin silane layers (less than 1 micron thickness). Such layers have good electrical conductivity and bare corrosion resistance. The influence of inhibiting additives on bare corrosion resistance was investigated too.
Project Objectives were:
- Minimal bare corrosion requirement for stand-alone conductive coating – cycling salt spray test in accordance with EUROCAE ED14/ RTCA DO160 Section 14.
- Electrical resistance – less than 5000 µOhm per sq. inch, when tested in accordance with procedure of MIL-DTL-81706B.
- Minimal corrosion resistance for small area of conductive coating on sheet with selective coating – 168 hours in SST (ASTM 117 and MIL-DTL-5541 Class 3).
- Dry and wet adhesion with aircraft paints – compliance with Fed-Std-141.
- Pot life of silane solution – minimum one month.
- Zero influence on strength and fatigue properties.
- Compliance with REACH and RoHS.
Project Results:
These are main S & T results/foregrounds:
1. New silane solution, based on modified commercial OXSILAN MG-0611 silane, was prepared The modification was done by reaction with commercial S264 silane. Traditional alcohol solvents were replaced by new ones (Dowanols) with significant higher flash point. Stability of the hydrolized silane and pot life of the solution were significantly increased. The mixture of two silanes didn't show significant improvement of corrosion resistance, and additionally it was found that S264 silane is more toxic, than OXSILAN MG-0611. Therefore, the investigation in this direction has been stopped, but the experience with Dowanol solvents was implemented in the all next experiments.
2. Three groups of potential inhibitors were selected for the process: silicates, triazols/imidazols, nano-containers. The screening tests (corrosion, electrical resistance and stability tests) for the solutions contains the inhibitors were performed. The solution contains of OXSILAN MG-0611 and silicate inhibitor didn't show corrosion resistance improvement relatively to OXSILAN MG-0611 standard solution and had low stability. The solutions with three nano-inhibitors were checked for corrosion resistance. The results showed clear improvement of the corrosion resistance by the N3 (R&D name) inhibitor, but due to absence of industrial supplier for these inhibitors, the investigation has been stopped. The solution contains traditional OXSILAN MG-0611 and the inhibitor from the triazole/imidazole group showed the improvement of corrosion resistance and was selected to continue to work with.
3. Rolled Elektron 43 magnesium sheet was purchased from Magnesium Elektron and investigated. Chemical composition of the sheet, electrical conductivity, tensile properties and bare corrosion resistance were tested. It has been found that surface of Elektron 43 from the first batch has impurities based on carbon (seems to be residue of rolling lubricant). These impurities seem to be the reason of low bare corrosion resistance results. The second batch of Electron 43 magnesium sheet was purchased and investigated for chemical composition, electrical conductivity, tensile properties and bare corrosion resistance. The chemical composition complain the supplier data. The second batch showed better bare corrosion resistance, lower electrical resistance and better mechanical properties than the first batch
4. Surface pretreatment technology has been developed basing on tested alkaline cleaner, deoxidizer and conditioner. The test result showed that state of the art deoxidizer |Ardrox 1227 does not provide required corrosion protection. Special deoxidizer NGA (R&D name) has been developed and applied for the project.
5. Samples of Elektron 43 sheet have been treated by the developed pretreatment technology and silane solution with selected inhibitor and then tested for corrosion resistance. Minimal bare corrosion requirement for stand-alone conductive coating – cycling salt spray test in accordance with EUROCAE ED14/ RTCA DO160 Section 14 was achieved. The new developed silane solution (OXSILAN MG-0611 +BT2) has improved corrosion resistance in SST. It stands 72 hour in SST (The traditional OXSILAN MG-0611 solution stands only 48 hours in SST). The specimen with OXSILAN MG-0611 modified with BT2 inhibitor meets the requirements for conductive coating according to the MIL-C-5541 before and after 72 hours in SST.
6. Selective coating technology, contains Ardrox®1770 anodize, OXSILAN MG-0611+BT2 conductive coating and aircraft paint on anodized surfaces, has been developed and implemented on the EL43 plates and Demonstrators. Corrosion resistance tests, paint adhesion tests, static and dynamic mechanical tests were performed on the samples from the EL43 magnesium sheet and on Demonstrators. Minimal corrosion resistance for small area of conductive coating on sheet with selective coating – 168 hours in SST (ASTM 117 and MIL-DTL-5541 Class 3) was achieved. The dry and wet adhesion tests with aircraft paints (Fed-Std-141) were passed. The thermo - mechanical process and the surface treatment don't decrease the material properties.
Potential Impact:
The development of the coating will provide to Aircraft Industry ability to design and manufacture magnesium secondary structures and system components with weight reduction of around 30-35%.
By achieving this objective, COMAG will facilitate obtaining the Clean Sky objectives of reduction in weight, fuel consumption, emissions of CO2 and NOX and the use of fully recyclable material. Since magnesium is 100% recyclable and is 35% lighter than aluminium a replacement of aluminium parts with magnesium parts will contribute to all the above mentioned goals.
Dissemination is planned through Aero-Magnesium website, talks with potential customers, international exhibitions and Clean Sky events.
List of Websites:
Mrs. Miri Moskovits, the scientific coordinator of the COMAG project and Head of Surface Treatments Laboratory in Aero-Magnesium is the point of contact for more information about of project work and results.
The main objective of this project was development and implementation of high corrosion resistance conductive coating for magnesium sheets in A/C. This coating should provide minimal bare corrosion requirement for stand-alone conductive coating – cycling salt spray test in accordance with EUROCAE ED14/ RTCA DO160 Section 14 - 48 hours in SST, 48 hours out of SST without rinse. This coating should provide corrosion resistance for electrical bonding scheme - small area of conductive coating on sheet with selective coating – 168 hours in SST (ASTM 117 and MIL-DTL-5541 Class 3). The coating won't influence strength and fatigue parameters of the substrate - high-strength magnesium sheet.
Project Context and Objectives:
CoMag project deals with development and implementation of high corrosion resistance conductive coating for magnesium sheets in A/C.
The development was based on very thin silane layers (less than 1 micron thickness). Such layers have good electrical conductivity and bare corrosion resistance. The influence of inhibiting additives on bare corrosion resistance was investigated too.
Project Objectives were:
- Minimal bare corrosion requirement for stand-alone conductive coating – cycling salt spray test in accordance with EUROCAE ED14/ RTCA DO160 Section 14.
- Electrical resistance – less than 5000 µOhm per sq. inch, when tested in accordance with procedure of MIL-DTL-81706B.
- Minimal corrosion resistance for small area of conductive coating on sheet with selective coating – 168 hours in SST (ASTM 117 and MIL-DTL-5541 Class 3).
- Dry and wet adhesion with aircraft paints – compliance with Fed-Std-141.
- Pot life of silane solution – minimum one month.
- Zero influence on strength and fatigue properties.
- Compliance with REACH and RoHS.
Project Results:
These are main S & T results/foregrounds:
1. New silane solution, based on modified commercial OXSILAN MG-0611 silane, was prepared The modification was done by reaction with commercial S264 silane. Traditional alcohol solvents were replaced by new ones (Dowanols) with significant higher flash point. Stability of the hydrolized silane and pot life of the solution were significantly increased. The mixture of two silanes didn't show significant improvement of corrosion resistance, and additionally it was found that S264 silane is more toxic, than OXSILAN MG-0611. Therefore, the investigation in this direction has been stopped, but the experience with Dowanol solvents was implemented in the all next experiments.
2. Three groups of potential inhibitors were selected for the process: silicates, triazols/imidazols, nano-containers. The screening tests (corrosion, electrical resistance and stability tests) for the solutions contains the inhibitors were performed. The solution contains of OXSILAN MG-0611 and silicate inhibitor didn't show corrosion resistance improvement relatively to OXSILAN MG-0611 standard solution and had low stability. The solutions with three nano-inhibitors were checked for corrosion resistance. The results showed clear improvement of the corrosion resistance by the N3 (R&D name) inhibitor, but due to absence of industrial supplier for these inhibitors, the investigation has been stopped. The solution contains traditional OXSILAN MG-0611 and the inhibitor from the triazole/imidazole group showed the improvement of corrosion resistance and was selected to continue to work with.
3. Rolled Elektron 43 magnesium sheet was purchased from Magnesium Elektron and investigated. Chemical composition of the sheet, electrical conductivity, tensile properties and bare corrosion resistance were tested. It has been found that surface of Elektron 43 from the first batch has impurities based on carbon (seems to be residue of rolling lubricant). These impurities seem to be the reason of low bare corrosion resistance results. The second batch of Electron 43 magnesium sheet was purchased and investigated for chemical composition, electrical conductivity, tensile properties and bare corrosion resistance. The chemical composition complain the supplier data. The second batch showed better bare corrosion resistance, lower electrical resistance and better mechanical properties than the first batch
4. Surface pretreatment technology has been developed basing on tested alkaline cleaner, deoxidizer and conditioner. The test result showed that state of the art deoxidizer |Ardrox 1227 does not provide required corrosion protection. Special deoxidizer NGA (R&D name) has been developed and applied for the project.
5. Samples of Elektron 43 sheet have been treated by the developed pretreatment technology and silane solution with selected inhibitor and then tested for corrosion resistance. Minimal bare corrosion requirement for stand-alone conductive coating – cycling salt spray test in accordance with EUROCAE ED14/ RTCA DO160 Section 14 was achieved. The new developed silane solution (OXSILAN MG-0611 +BT2) has improved corrosion resistance in SST. It stands 72 hour in SST (The traditional OXSILAN MG-0611 solution stands only 48 hours in SST). The specimen with OXSILAN MG-0611 modified with BT2 inhibitor meets the requirements for conductive coating according to the MIL-C-5541 before and after 72 hours in SST.
6. Selective coating technology, contains Ardrox®1770 anodize, OXSILAN MG-0611+BT2 conductive coating and aircraft paint on anodized surfaces, has been developed and implemented on the EL43 plates and Demonstrators. Corrosion resistance tests, paint adhesion tests, static and dynamic mechanical tests were performed on the samples from the EL43 magnesium sheet and on Demonstrators. Minimal corrosion resistance for small area of conductive coating on sheet with selective coating – 168 hours in SST (ASTM 117 and MIL-DTL-5541 Class 3) was achieved. The dry and wet adhesion tests with aircraft paints (Fed-Std-141) were passed. The thermo - mechanical process and the surface treatment don't decrease the material properties.
Potential Impact:
The development of the coating will provide to Aircraft Industry ability to design and manufacture magnesium secondary structures and system components with weight reduction of around 30-35%.
By achieving this objective, COMAG will facilitate obtaining the Clean Sky objectives of reduction in weight, fuel consumption, emissions of CO2 and NOX and the use of fully recyclable material. Since magnesium is 100% recyclable and is 35% lighter than aluminium a replacement of aluminium parts with magnesium parts will contribute to all the above mentioned goals.
Dissemination is planned through Aero-Magnesium website, talks with potential customers, international exhibitions and Clean Sky events.
List of Websites:
Mrs. Miri Moskovits, the scientific coordinator of the COMAG project and Head of Surface Treatments Laboratory in Aero-Magnesium is the point of contact for more information about of project work and results.