Researchers develop new aluminium powder for foamable WAAM wire

Researchers at Leibniz University Hannover in Germany have developed a custom aluminium alloy and produced pre-alloyed powder using Electrode Induction Melting Inert Gas Atomisation (EIGA), with the material being developed for metallic foams and, ultimately, foamable wire for Wire Arc Additive Manufacturing (WAAM).

The research, published in The International Journal of Advanced Manufacturing Technology, focused on creating an aluminium alloy with a melting range suitable for producing metal foams while retaining enough workability for subsequent extrusion into thin wire.

Metal foams offer a combination of low density, stiffness, energy absorption, and damping. One established powder metallurgy route involves combining metal powder with a blowing agent and compacting the mixture into a precursor. When heated, the blowing agent releases gas, causing the material to expand into a porous structure.

AlMg2Si1.2 powder developed for foam production

For the study, researchers developed AlMg2Si1.2, an alloy containing nominally 2 wt. per cent magnesium and 1.2 wt. per cent silicon.

Thermodynamic calculations were used to determine a composition with less than 5 wt. per cent alloying elements and a liquidus temperature below the main hydrogen-release peak of pre-treated titanium hydride (TiH2), which served as the blowing agent.

The alloy was initially cast into cylindrical billets, then extruded into rods and machined into electrodes. Researchers processed the electrodes using an EIGA 70-500/VIGA 2B inert gas atomisation system from ALD Vacuum Technologies.

Five atomisation runs were conducted using argon at pressures ranging from 16.8 to 23.0 bar. Higher atomisation pressure reduced the median particle size from 51 µm to 40 µm.

The resulting powder particles were predominantly spherical. The 63–90 µm fraction recorded the best flow properties.

One batch produced at 20.3 bar was selected for further testing because of its stable atomisation conditions and particle size distribution. It had d10, d50, and d90 values of 20 µm, 44 µm, and 76 µm, respectively.

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Powder produces highly porous aluminium foam

Differential scanning calorimetry measured the alloy's solidus temperature at 560 ± 2°C and its liquidus temperature at 646 ± 2°C.

This melting range overlapped with hydrogen release from TiH₂ that had been pre-treated in air at 480°C for 180 minutes, supporting its use in the foam-production process.

To test the material’s foamability, researchers mixed selected powder fractions with 0.7 wt. per cent TiH₂ and compacted them into precursors. These were then heated to produce foam samples.

X-ray microscopy recorded porosities between 64.1 per cent and 67.7 per cent. Researchers found no statistically significant difference in either porosity or median pore size between foams made using the 45–63 µm and 63–90 µm powder fractions.

The researchers concluded that AlMg2Si1.2 powder provides a suitable basis for producing foamable material through powder metallurgy.

Next step: foamable wire for WAAM

The next stage of the work is focused on extruding the aluminium powder into foamable wire and integrating the wire into a WAAM process.

The longer-term concept is to deposit the foamable wire first and then apply a secondary heat source to selectively foam the deposited material.

If successful, this approach could allow WAAM components to combine dense and porous regions, with properties tailored locally within the same component.

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