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Innovative Al alloy For aircraft structural parts using Additive MAnufacturing technology

Periodic Reporting for period 3 - AlForAMA (Innovative Al alloy For aircraft structural parts using Additive MAnufacturing technology)

Reporting period: 2020-07-01 to 2021-03-31

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.
WP1 addressed the definition of innovative high strength aluminium alloys to be produced. Four approaches were selected: two based on 7xxx series Al alloys, adding 4wt% of Si and 0.5-1.5wt%of Zr to improve the processability of the original alloy, and two other approaches based on AlSi10Mg alloy, adding 4wt% of Cu and 4-8wt% of TiB2 particles to improve the mechanical properties.

WP2 and WP3 included new powder manufacturing development and AM process optimization to select the most suitable Al alloy.
- All approaches were produced by atomization process. The approaches selected included: Al7075+4%Si, Al7075+1%Zr and AlSi10Mg+4%Cu.
- All the powders manufactured were processed by SLM.
- The feasibility of producing this customized alloy at industrial scale was analysed through industrial providers. 90kg of AlSi10Mg+4%Cu was atomised at industrial scale facility.

WP4 was focused on the thermal treatment cycle optimization for mechanical properties improvement.
- Thermally treated samples were characterized by microscopy
- The thermal treatment was optimized to obtain the maximum microhardness value

In WP5 and WP6 characterization of the innovative Al alloy was performed to determine the behaviour of the material produced by AM.
- Testing conditions and sample geometry were defined for static, fatigue and corrosion trials.
- Testing samples and demonstrator component were manufactured by SLM in optimized AlSi10Mg+4%Cu alloy.
- Mechanical properties and corrosion resistance of the optimized alloy were determined
- Demonstrator components characterization was performed.

Several dissemination activities were performed:
- Project website
- An executive summary published in CORDIS
- Social media post
- A poster for an additive manufacturing event in Portugal
- Interaction with other European projects
- Oral presentations in workshops and scientific conferences
- Publications

3 exploitable results were obtained.
ALFORAMA aims at developing a new material to respond to the lightness requirements and thus, be compliant with the environmental demands by reducing fuel consumption and being less polluting. This will contribute to reinforce the European aeronautic industry to keep at the forefront of the sector.

The main outcomes considered as unconventional methodologies and innovations to support the industrial impacts are:
• Know-how on design of alloys for additive manufacturing
• Powder atomization technology of light Aluminium alloys developed with tailored and improved final properties
• Definition of the optimized powder characteristics, both in terms of powder composition and morphology to optimize the SLM processing of particle reinforced Al alloys
• Computational methodology, including thermodynamic and kinetic calculations, to optimize Al based metal alloys compositions that are more suitable for SLM processing.
• Development of SLM processing for innovative High Strength Al alloys with improved mechanical, 30% higher, compared to conventional cast grades alloys.
• Define a protocol for the optimization of heat treatments of new Al alloys, with tailored composition, in order to improve final mechanical properties (30% after the optimized heat treatment).
• Determine mechanical properties and corrosion behaviour of newly developed Al alloy. Analyse the influence of process related issues, such as residual porosity, subsurface porosity, residual stresses, build orientation and surface condition on the overall performance of AM manufactured samples. For the new tailored alloy based on the conventional Al7075 composition, the cracking susceptibility has reduced in a 95%.
Reduction of crack susceptibility after the addition of Zr to Al7075 processed by SLM
Al7075 processed by SLM with high quantity of cracks
Comparison in microhardness between SLM processed conventional and modified alloys