There is a need in aeronautic industry to develop innovative high performance aluminum alloys feasible by powder metallurgy and to develop Additive Manufacturing (AM) processes for such alloys while obtaining the requested characteristics in terms of mechanical strength and corrosion resistance. Such developments aim at developing lighter structures that will contribute in further reductions in fuel consumption, CO2 and NOx emissions.
AlForAMA project is part of Clean Sky 2 initiative, and it is included on REG IADP, in which the objective is to bring the integration of technologies for Regional Aircraft to a further level of complexity with respect to the achievements of Clean Sky GRA.
The main goal of the project is to develop an innovative High Strength Al alloy, feasible by powder metallurgy and suitable for Selective Laser Melting (SLM), with improved weldability and increased mechanical and corrosion resistance in comparison to cast grades Al alloys currently employed in AM.
The specific technical objectives of the project are:
1. Design the chemical composition of innovative High strength Al alloys for aeronautics
2. Develop a gas atomization process to obtain an Al powder with the new developed chemical composition and suitable for AM manufacturing
3. Develop a mixing process to ensure the preparation of a homogeneous powder mixture with sufficiently high flowability
4. Define the most critical variables for an optimized SLM process to ensure defect free material manufacturing
5. Thermal treatment optimization to improve the mechanical performances and corrosion resistance of the new alloy
6. Thermodynamic analysis methodologies to improve the phase structure during AM processing and subsequent heat treatment
7. Investigate the SLM material behaviour
8. Validate the developed SLM and heat treatment methodology in a use case
After the complexion of the project, the following conclusions were reached:
- Three different tailored high strength aluminium alloys composition approaches were developed to be implemented by SLM.
- The composition of the three alloys was optimised by thermodynamic simulations to improve the solidification range and phase transformation to achieve the target mechanical properties.
- For each approach an experimental powder batch was manufactured using a lab scale atomizer. The atomized powder batches show very good rheological properties similar to the target ones and were suitable for further SLM processing.
- The addition of Si and Zr to obtain a new Al7075 alloy is effective in the microstructure refinement and avoids cracks when processing by SLM.
- The addition of Cu to obtain a new AlSi10Mg + Cu alloy promotes the precipitation of CuAl2 strengthening phase.
- After a thermal treatment optimization, Al7075+Zr and AlSi10Mg+Cu tailored alloys presented a hardness value similar to a wrought Al7075 T6 condition.
- A large powder batch of AlSi10Mg+Cu was atomized in an industrial scale atomizer to check the scalability of the atomization procedure.
- Two aeronautical components were manufactured by SLM with the high strength alloy.
To conclude, different approaches for High Strength Al alloy, feasible by powder metallurgy and suitable for SLM, have been developed. The different developments show an improved processability by SLM, obtaining a defect free material in all cases. Two of the alloys developed in the project have the potential of achieving the mechanical requirements needed in the aerospace industry, defined by Al7075 wrought alloy, so could have a high impact in the sector. A deep mechanical characterization has been carried out for the most promising alloy, AlSi10Mg+Cu, and it has been demonstrated that it is possible to manufacture a high strength aluminium alloy component, defect free, by SLM.
