Fraunhofer Institute for Mechanics of Materials IWMRadial compressor impellers made of the 2618A aluminum alloy are standard in exhaust gas turbochargers. However, new hydrogen-based powertrains generate significantly more water vapor and more aggressive condensates than conventional internal combustion engines. Until now, it was unknown whether this proven alloy could withstand these new stresses. Fraunhofer IWM, in collaboration with BAM, is investigating stress corrosion cracking and its interaction with fatigue - thereby creating the data foundation that manufacturers need for safe use in fuel cell and H2 engine applications.
Verification of the structural durability of an aluminum rotor material for powering hydrogen-based energy conversion systems – influence of moisture and corrosive condensates
Ongoing research project
Project description
Market needs and challenges
The transition to hydrogen-based propulsion systems, such as PEM fuel cells and engines that burn hydrogen or ammonia, is fundamentally changing the operating environment of centrifugal compressor impellers: significantly higher water vapor content and, in some cases, acidic condensates come into contact with the established 2618A aluminum alloy. Whether this leads to stress corrosion cracking or hydrogen embrittlement has not yet been scientifically investigated. This poses a significant risk for manufacturers who wish to continue using this proven alloy, for which there is no alternative.
Project approach
Fraunhofer IWM and BAM are systematically characterizing the corrosion and stress-corrosion cracking behavior of 2618A under conditions close to actual use: electrochemical investigations, short-term and long-term stress-corrosion cracking tests, and LCF fatigue tests in water vapor and hydrogen atmospheres. This is supplemented by microscopic analyses (AFM, fractography) to elucidate the damage mechanisms, as well as component tests on actual compressor impellers.
Contribution to addressing challenges
The result is the first robust database documenting the wet corrosion and SpRK behavior of 2618A under operational, hydrogen-relevant conditions. Manufacturers can thus make informed assessments of whether and under what conditions the alloy can continue to be used - a direct contribution to the safe and economical design of turbo components for the hydrogen economy.
Fraunhofer IWM’s work packages in the project:
Fraunhofer IWM is conducting short-term testing of the SpRK sensitivity of notched specimens under constant deflection, as well as tensile tests at slow strain rates as a screening method for SpRK susceptibility in water vapor and reference condensate. The core of the project is the long-term SpRK testing (>10,000 h) of smooth and notched specimens under defined water vapor partial pressure at 90 °C and 150 °C, including the potential determination of threshold values. In addition, Fraunhofer IWM is investigating the interaction between LCF loading and wet corrosion on notched specimens, in which fatigue cycling is interrupted by wet corrosion phases. The final results will include: reliable SpRK parameters for various materials conditions (T61, aged, and, if applicable, T7x); a clear picture of damage mechanisms based on fractographic analyses; and an evaluation of the interaction between fatigue and corrosion - all directly applicable to component design.
Based on the project results, Fraunhofer IWM can offer industrial companies the following research and development services:
Testing for stress corrosion cracking under conditions closely resembling actual operating environments
Long-term and short-term testing of the stress corrosion cracking susceptibility of aluminum alloys in water vapor and condensates for realistic service life estimates for new operating environments.
Screening tests at slow strain rates
Rapid assessment of the environmental sensitivity of materials within a few days.
Evaluation of the interaction between fatigue and corrosion
Investigation of how microcrack formation and wet corrosion reinforce each other to gain practical insights for the design and operation of cyclically loaded components.
Provision of materials data for aluminum rotor materials
Reliable property data on 2618A under the influence of hydrogen and water vapor for the design of turbochargers and fuel cell components.
Fractographic and microstructural damage analysis
Examination of fracture surfaces to elucidate failure mechanisms.
Consulting on materials selection for hydrogen-based applications
Well-founded assessment of whether and under what conditions existing aluminum alloys can continue to be used, in order to reduce development risks during the transition to green propulsion systems.
