High-strength (and high-temperature-resistant) aluminum alloys for primary forming in lightweight construction

Project description

Casting and powder-bed-based additive manufacturing (LPBF) offer enormous potential for lightweight construction due to their high degree of geometric freedom and monolithic production. At present, these direct-forming processes are primarily available for aluminium–silicon (Al–Si) alloys, whose strength of 200 to 250 megapascals (MPa) is about half that of high-strength wrought alloys. The only high-strength LPBF alloy, Scalmalloy® (approximately 500 megapascals), is currently considered cost-prohibitive for mass-production applications because it contains the rare and expensive element scandium. Furthermore, the strength of conventional casting alloys decreases drastically above 200 degrees Celsius, which represents a significant opportunity for improving engine components and other thermally stressed parts.

HAlUr pursued the development of fundamentally new aluminum alloys based on the previously little-studied eutectic systems Al-Co, Al-Ni and Al-Ca - which had previously been scarcely researched. Compared to Al-Si, these base systems offer higher base strength and, through the targeted addition of hardening and mixed-crystal-strengthening elements, enable a property profile of ≥ 500 megapascals at room temperature (with ≥ 10 percent elongation at break) as well as ≥ 150 megapascals at 300 degrees Celsius. The core methodology involves the close integration of digital materials modeling (thermodynamics, density functional theory (DFT), atomistics) with experimental Rapid Alloy Development (RAD) using laser materials deposition (LMD). 

Fraunhofer IWM Work Packages:

Digital Materials Modeling and Alloy Development
Using thermodynamic methods (Calculation of Phase Diagrams (CALPHAD)), the team calculated phase diagrams, melting intervals, solubilities and phase stabilities of the new Al-Co, Al-Ni and Al-Ca base systems with various alloying elements. In addition, atomistic calculations based on density functional theory (DFT, Vienna Ab initio Simulation Package (VASP), Quantum ESPRESSO) were used to predict physical, mechanical and chemical properties such as lattice stability, cohesive energies and corrosion resistance.

LPBF Process Simulation
Fraunhofer IWM contributed a proprietary particle-based simulation technique (Smoothed Particle Hydrodynamics, SPH) for the LPBF process. This technique enables 3D simulation of melting and solidification behavior at the powder particle scale, taking into account energy input, heat conduction, surface tension and Marangoni flow. This made it possible to predict the porosity, hot cracking susceptibility and surface roughness of the new alloys on a process-specific basis and to derive recommendations for process control.

Materials Characterization, Demonstrator Testing and Evaluation
This includes microstructural analyses (scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), electron backscatter diffraction (EBSD), X-ray diffraction (XRD) and optical microscopy), the determination of mechanical properties (tensile strength, hot tensile strength, elongation at break and fatigue strength) and thermophysical characterizations.