What Is It About Aluminum Foam?

Recently one of Europe’s most important industrial research centers touted an unusual material for housing electric vehicle batteries: lightweight, impact-resistant, and heat-resistant. The housings exhibited by Fraunhofer Institute for Machine Tools and Forming Technology and its research partner Amsted Automotive are formed as sandwiches of solid aluminum sheets encasing “aluminum foam”.

If needed, these sandwiches can incorporate a cooling structure or thermal storage medium called Phase Change Material (PCM) that will store or release heat as it changes between solid and liquid states. PCM can absorb or release large amounts of thermal energy while changing its state (solid to liquid or vice versa) without significantly altering its own temperature. This makes the structure, and that foam, well-suited for thermal management in lithium-ion batteries, the most common fuel-cell type in current EV models.

The battery housing is not the only application where metal foam has prospects: the lightness and sturdiness may also have value for aerospace components and structures; and may be effective as a material for machine noise prevention.  A 100-mm thick polyurethane foam has a sound-insulating value of 23 dB, whereas a 20-mm thick aluminum foam panel has a value of 30 dB, one study has concluded.

Aluminum foam is characterized by a porous structure in which gas-filled voids are dispersed throughout a solid metal matrix. These materials are categorized as open-cell or closed-cell foams, depending on whether the pores are interconnected. Closed-cell aluminum foams trap gas in sealed pockets, and are useful in structural and energy-absorbing applications due to their higher stiffness and resistance to fluid infiltration. Open-cell foams allow fluid flow and are useful in filtration, heat exchange, and acoustic damping.

Manufacturing methods for aluminum foam vary, but most processes rely on introducing a foaming agent into molten aluminum or stabilizing gas bubbles in a semi-solid slurry. One technique involves adding titanium hydride (TiH_₂), which decomposes at high temperatures to release hydrogen gas, forming bubbles within the melt.

A process similar to investment casting involves polymer foam coated with ceramic slurry and fired to create a porous mold: Molten metal is cast into that mold, resulting in an open-cell metal foam that replicates the polymer structure.

In another method a mixture of aluminum powder and foaming agents is compacted, and then heated to induce expansion. Control over pore size distribution, density, and uniformity is critical, as these parameters directly influence mechanical and functional properties.

It should be noted that “foam” structures can be achieved by additive manufacturing, too.

Aluminum foam retains many of the properties of aluminum, such as corrosion resistance and thermal conductivity, while offering improved damping characteristics. Some automakers specify aluminum foam for crash management systems, including bumper cores, side-impact protection beams, and crumple zones. Its ability to absorb kinetic energy efficiently helps reduce peak forces transmitted to passengers during collisions.

Similarly, aluminum foam sandwich plates are used in armor for military vehicles to offset shock waves from incendiary blasts.

In aerospace applications, aluminum foam sandwich panels and structural components offer value thanks a high stiffness-to-weight ratio.

Another important application is in thermal management systems. Open-cell aluminum foams have high surface area and good thermal conductivity, so they’re effective heat exchangers and heat sinks in electronics and industrial equipment.

Production cost and scalability remain challenges compared to conventional materials, but with so many advantageous qualities the prospects for aluminum foam deserve wider attention.