Periodic Reporting for period 2 - Cr Free REAL (Development and testing of innovative Cr Free solution for REmoval of Anodic Layers)
Reporting period: 2020-04-01 to 2021-09-30
Aluminium alloys are widely used in aeronautical applications for airframe and for on-board systems. Most of the aluminium parts (95%) used in aircraft are treated against corrosion or to withstand various mechanical deterioration conditions, depending of their final use, with Cr(VI) based treatments. For repair and maintenance, the removal of the protective coating must be performed. Coating removal may also be needed in serial production for the aluminium parts when such parts are not sufficiently well coated and are requiring a re-coating.
For stripping of alumium oxide layers the state of the art industrial processes use are Cr(VI) based agents (e.g. phosphorchromic or sulphochromic acid). Such agents remove the oxide layer, with no or only minimal attack to the surface of the aluminium substrate due to inhibition of the attack by the chromic acid. State of the art (semi-)industrial approaches are using NaOH as Cr(VI)-free stripping agent. The major drawback of this process is the high dependence on the layer thickness to be removed. Too long stripping time leads to attack of the substrate and thus to deterioration of the fatigue properties of the stripped parts. Since the use of Cr(VI) will be prohibited from 2024, a Cr free solution must be found for the removal of the oxide layers.
The innovative green and eco-friendly process developed to strip anodic layer or chemical conversion layer allows reducing risks for human health and for the environment by:
• reducing the use of hazardous substances during stripping operation with the suppression of Cr(VI) substances
• improving the environmental record of the new process in comparison with the chromated one.
The successful implementation of a Cr free process complies with the existing regulations (e.g. REACH), is environmentally friendly and increases the safety in operation.
Cr Free REAL project main objective were to develop and test a suitable REACH compliant Cr(VI)-free process for removal of anodic layers.
The following specific objectives were pursued in the Cr Free REAL project:
1. Define overall requirements
2. Evaluation of existing stripping processes
3. Develop innovative Cr free stripping processes
4. Re-treated samples performance
5. Ranking
6. Implementation on alternative aluminium alloys
For stripping of alumium oxide layers the state of the art industrial processes use are Cr(VI) based agents (e.g. phosphorchromic or sulphochromic acid). Such agents remove the oxide layer, with no or only minimal attack to the surface of the aluminium substrate due to inhibition of the attack by the chromic acid. State of the art (semi-)industrial approaches are using NaOH as Cr(VI)-free stripping agent. The major drawback of this process is the high dependence on the layer thickness to be removed. Too long stripping time leads to attack of the substrate and thus to deterioration of the fatigue properties of the stripped parts. Since the use of Cr(VI) will be prohibited from 2024, a Cr free solution must be found for the removal of the oxide layers.
The innovative green and eco-friendly process developed to strip anodic layer or chemical conversion layer allows reducing risks for human health and for the environment by:
• reducing the use of hazardous substances during stripping operation with the suppression of Cr(VI) substances
• improving the environmental record of the new process in comparison with the chromated one.
The successful implementation of a Cr free process complies with the existing regulations (e.g. REACH), is environmentally friendly and increases the safety in operation.
Cr Free REAL project main objective were to develop and test a suitable REACH compliant Cr(VI)-free process for removal of anodic layers.
The following specific objectives were pursued in the Cr Free REAL project:
1. Define overall requirements
2. Evaluation of existing stripping processes
3. Develop innovative Cr free stripping processes
4. Re-treated samples performance
5. Ranking
6. Implementation on alternative aluminium alloys
The main result of the Cr Free REAL project is a green, innovative, REACH compliant process that assure the removal of the oxide layers (anodised and conversion coatings with and without Cr(VI)) from five types of aluminium alloys. The high performance of the Cr free process was proven at lab and semi-industrial scale for samples with complex geometries.
The main technical achievements of the Cr Free REAL project are:
• Development of an innovative, environmentally friendly, Cr(VI)-free process for oxide layers removal with acidic stripping agents enhanced with functional additives
• A deep understanding of the mechanisms of the stripping processes (oxide layer removal, attack of the substrate and inhibition of such attacks) and the effect of various process parameters during the stripping process
• A universal, green process, suitable for substrates of various types of machined and cast aluminium alloys and for removal of Cr(VI)-free and Cr(VI)-based oxide layers
• A uniform removal of the oxide layers without attack on the substrate was achieved as a function of immersion time
• Cr Free REAL stripping process has reduced effects on recoated parts properties, showing good performance against corrosion for multiple cases
• A process that enables Cr(VI)-free green operation modes for re-working of out-of-specification oxide layer coatings in the production process and for ground-based repair and maintenance operations
• Generated knowledge could be furthermore developed and adapted to other industrial requirements
Project achievements were disseminated as oral presentations to various international conferences (e.g. EUROCORR, EUROMAT). A follow-up project is foreseen to further increase innovation TRL level.
The Cr Free REAL project acknowledged the funding received from H2020, Clean Sky 2 program: “The research leading to these results has received funding from the European Community’s H2020 for the Clean Sky joint technology initiative under grant agreement no. 831991”.
The main technical achievements of the Cr Free REAL project are:
• Development of an innovative, environmentally friendly, Cr(VI)-free process for oxide layers removal with acidic stripping agents enhanced with functional additives
• A deep understanding of the mechanisms of the stripping processes (oxide layer removal, attack of the substrate and inhibition of such attacks) and the effect of various process parameters during the stripping process
• A universal, green process, suitable for substrates of various types of machined and cast aluminium alloys and for removal of Cr(VI)-free and Cr(VI)-based oxide layers
• A uniform removal of the oxide layers without attack on the substrate was achieved as a function of immersion time
• Cr Free REAL stripping process has reduced effects on recoated parts properties, showing good performance against corrosion for multiple cases
• A process that enables Cr(VI)-free green operation modes for re-working of out-of-specification oxide layer coatings in the production process and for ground-based repair and maintenance operations
• Generated knowledge could be furthermore developed and adapted to other industrial requirements
Project achievements were disseminated as oral presentations to various international conferences (e.g. EUROCORR, EUROMAT). A follow-up project is foreseen to further increase innovation TRL level.
The Cr Free REAL project acknowledged the funding received from H2020, Clean Sky 2 program: “The research leading to these results has received funding from the European Community’s H2020 for the Clean Sky joint technology initiative under grant agreement no. 831991”.
One of the major challenges for the aeronautics industry by 2024 is to propose new technological solutions to meet environmental regulations.
In the Cr Free REAL project, the employment of Cr free, environmentally friendly processes for the removal of oxide layers was thoroughly studied, analysed and investigated for its applicability in the 1. aircraft Maintenance, Repair and Overhaul – parts damaged due to use and for 2. new components, which exhibits defects at fabrication point. Cr Free REAL allows to maintain and even improve mobility avoiding a complexification of maintenance. A short maintenance time implies a faster turnaround time for aircraft. A REACH compliant process available latest in 2024 avoids the offshoring of surface treatment supply chain and the associated risk of dependencies on offshored subcontractors and delays of maintenance services. The Cr Free REAL project allows to maintain surface treatment activities in Europe and thereby to maintain and strengthen the competitiveness of Europe. The newly develop Cr free stripping process serves as a suitable solution, with impact on reducing the use of row material (aluminium). Cr Free REAL innovative green and eco-friendly stripping process allows reducing risks for human health and for the environment by 1.) reducing the use of hazardous substances during stripping operation with the suppression of Cr(VI) substances (classified CMR) and 2.) improving the environmental record of the new process in comparison with the chromated one.
Beyond aeronautical applications, the Cr free process developed in Cr Free REAL project can be successfully applied in other sectors (e.g. automotive, railway), where aluminium alloy components are used.
The further development of the technology pushed by Cr free REAL project will allow exploiting benefits in other possible applications domains, allowing for cross-fertilisation between aviation and other technological areas.
In the Cr Free REAL project, the employment of Cr free, environmentally friendly processes for the removal of oxide layers was thoroughly studied, analysed and investigated for its applicability in the 1. aircraft Maintenance, Repair and Overhaul – parts damaged due to use and for 2. new components, which exhibits defects at fabrication point. Cr Free REAL allows to maintain and even improve mobility avoiding a complexification of maintenance. A short maintenance time implies a faster turnaround time for aircraft. A REACH compliant process available latest in 2024 avoids the offshoring of surface treatment supply chain and the associated risk of dependencies on offshored subcontractors and delays of maintenance services. The Cr Free REAL project allows to maintain surface treatment activities in Europe and thereby to maintain and strengthen the competitiveness of Europe. The newly develop Cr free stripping process serves as a suitable solution, with impact on reducing the use of row material (aluminium). Cr Free REAL innovative green and eco-friendly stripping process allows reducing risks for human health and for the environment by 1.) reducing the use of hazardous substances during stripping operation with the suppression of Cr(VI) substances (classified CMR) and 2.) improving the environmental record of the new process in comparison with the chromated one.
Beyond aeronautical applications, the Cr free process developed in Cr Free REAL project can be successfully applied in other sectors (e.g. automotive, railway), where aluminium alloy components are used.
The further development of the technology pushed by Cr free REAL project will allow exploiting benefits in other possible applications domains, allowing for cross-fertilisation between aviation and other technological areas.