Aluminum foam in the automotive industry

Why is aluminum foam suited to crash-relevant areas of the vehicle?

Aluminum foam absorbs crash energy through plastic deformation: in a crash the material takes up large amounts of energy before it is impaired. Filling steel profiles with aluminum foam greatly improves their buckling and compression behavior while saving weight. Added to this are excellent vibration damping, for example against engine vibrations, and the recyclability of the purely metallic material.

The use of aluminum foam increases the torsional stiffness of the complete body by about 10 %.

Which vehicle components are built with aluminum foam?

Aluminum foam is used as a reinforcing element in the body area, wherever stiffness and crash behavior are needed together: in foamed bumpers, node areas and joints, in side impact protection, in door sills, in roof rails, side members and cross members, and in panel elements such as roof bows. Added to these are ready-to-install 3D shaped elements, such as crash absorbers and shaped elements for shock absorbers.

Documented application example: the aluminum foam crash absorber in the luggage net of a passenger car (3D shaped element).

Why is the aluminum foam battery box suited to electric vehicles?

The battery box from the Havel Lite® series is made entirely of aluminum foam sandwiches. Low weight, good crash behavior, high bending stiffness and scope for temperature regulation make this newly developed component well suited to modern vehicle manufacturing. Webs in the form of aluminum foam sandwiches between the batteries act as spacers and crash absorbers; profiles or tubes can be integrated into the aluminum foam, for example for battery cooling. The housing is watertight, repairable, 100 % recyclable and provides good electromagnetic shielding.

Example element of aluminum foam: dimensions 975 mm × 536 mm × 55 mm, material thickness 4 mm; the crash behavior is shown to the standard DIN 50134, compression test of metallic cellular materials.

How has aluminum foam battery protection been tested and classified?

The energy absorption and good crash behavior of the battery box have been tested with a side crash test and a bollard test, the bollard test both in simulation and in physical tests. In the EVERSAFE project, an underbody impact was examined both in simulation and in physical tests: a vehicle with a mass of 943 kg drives at 40 km/h over a semicircular obstacle whose highest point lies above the lowest point of the battery box, so that driving over it subjects the housing to an impact load. The aluminum foam was developed further for the requirements of the Chinese standard GB 38031 (2020) and the European standard ECE 100; integrating fiber mats increases the fire protection. Both are standards that products are tested against, not certifications held by Havel metal foam.

Havel metal foam has carried out internal impact tests on aluminum foam sandwich panels developed specifically as a protective solution for batteries, with consistently positive results for stability and protective effect (benchmark: the Chinese standard GB 38031).

Non-combustible

DIN EN 45545-2: classified HL3 (material testing of AAS and SAS); no certificate was applied for.

No toxic gases

The build-up is purely metallic, with no plastics and no adhesives.

Crash behavior

Energy absorption and good crash behavior, tested with a side crash test and a bollard test, the bollard test both in simulation and in physical tests.

How does an aluminum foam battery box regulate the battery temperature?

With lithium-ion batteries in electric vehicles, three thermal limits have to be observed: below 0 °C the performance of the battery, and with it the range, drops considerably; above 30 °C aging increases sharply; above 40 °C irreversible damage can occur. Tubes and profiles can be integrated into the metal foam, making use of aluminum's good thermal conductivity: the internal cavities created in this way serve to route additional lines or to let media flow directly through to cool or heat the battery cells.

When the tube system is foamed directly into the metal foam core, a metallurgical bond to the cover sheets is possible; when it is inserted afterwards, the cover sheets are bonded to the metal foam with adhesive.

Which vehicle components has Havel metal foam built so far?

Fourteen components from Havel metal foam's own application catalog show where the material already sits in the vehicle: battery protection plates, base plates and cover plates, cooling plates and pack separators, foamed sills, floors for turntable ladders and articulated buses, a frame for hydrogen tanks and the rear underrun protection. Each card gives the build-up, the dimensions, the mass and the maturity, that is, whether the part is in series production, was built as a prototype or is a study. The range extends from series production of more than 3,500 units to a design draft; which manufacturer and which vehicle are behind it is not stated here.

How does aluminum foam meet the new requirements for truck underrun protection?

The responsible body of the United Nations Economic Commission for Europe (UNECE) adopted the 03 series of amendments to UNECE Regulation No. 58 for underrun protection devices: underrun protection for trucks must now not only have different geometric properties from before, but must also withstand test forces almost twice as high in a strength test, for all vehicles placed on the market from September 2021 at the latest. The requirements were tightened above all for heavy commercial vehicles (N2, N3, O3, O4). Foaming the relevant profiles with a metallurgical bond leads to an enormous increase in stiffness and strength and to higher energy absorption on impact; the 3D foam parts can be pushed into existing underrun protection profiles, so that these also meet the new requirements.