Aluminum foam vs. aluminum vs. steel
The core difference in one figure: a plate of 1,000 × 1,000 × 10 mm³ weighs 78.5 kg in steel (S235JR), 27 kg in aluminum (EN-AW 5754) and 5 to 8 kg in aluminum foam. Steel remains the stiffest material (Young's modulus 210 GPa); aluminum foam, on the other hand, is non-combustible, absorbs energy, damps sound and is 100 % recyclable. In a sandwich with steel cover layers, as SAS 10-1-1 (1 mm steel cover layers, foam core 0.7 g/cm³), the foam forms the core, the stiffness comes from the steel cover layers (Young's modulus 210 GPa), and the plate weighs 21.3 kg instead of 78.5 kg.
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How do aluminum foam, aluminum and steel differ in their material values?
The table sets steel S235JR, soft aluminum EN-AW 5754 (AlMg3) and aluminum foam (AlSi10) side by side, together with the two sandwich designs AAS (aluminum cover layers) and SAS (steel cover layers) in the 1/8/1 build-up. All values are analytically determined guide values; for a specific application they must be determined for that application.
| Property | Unit | Steel (S235JR) | Aluminum (EN-AW 5754) | AAS (aluminum cover layers) | SAS (steel cover layers) | Aluminum foam (AlSi10) |
|---|---|---|---|---|---|---|
| Density | g/cm³ | 7.85 | 2.7 | 0.5 to 0.8 (core) · 2.7 (cover layer) | 0.7 (core) · 7.85 (cover layer) | 0.5 to 0.8 |
| Young's modulus | GPa | 210 | 70 | 0.33 to 0.76 (core) · 70 (cover layers) | 0.6 (core) · 210 (cover layers) | 0.33 to 0.76 |
| Poisson's ratio | - | 0.3 | 0.34 | 0.3 to 0.34 | 0.31 to 0.34 | 0.31 to 0.34 |
| Compressive strength | N/mm² | - | - | 2.5 to 10 (core) | 8.5 (core) | 2.5 to 10 |
| Yield strength | N/mm² | 235 | 100 | - | 140 to 280 (cover layer) | - |
| Tensile strength | N/mm² | 340 | 180 | 120 to 200 | 270 to 410 (cover layer) | 4 to 6.3** |
| Bending stiffness | mm/1,000 N | 1.2 | 3.6 | 6.8** | 2.4 | 22 to 41** |
| Thermal conductivity | W/mK | 48 to 58 | 170 to 220 | 10 to 15 (core) · 170 to 220 (cover layer) | 25 (core) · 48 to 58 (cover layer) | 12 to 36 |
| Mass 1,000 × 1,000 × 10 mm³ | kg | 78.5 | 27 | about 11 (AAS 10-1-1, core 0.7 g/cm³)* | 21.3 (SAS 10-1-1, core 0.7 g/cm³) | 5 to 8* |
The foam is regularly produced at 0.5 to 0.8 g/cm³, higher densities by agreement. Young's modulus and compressive strength of the foam core are given by density according to the AAS, SAS and Havel Lite® product data sheets (0.5 g/cm³ → 330 N/mm² / 2.5 N/mm² · 0.6 → 450 / 6.5 · 0.7 → 600 / 8.5 · 0.8 → 760 / 10); the SAS column gives the value for this build-up's core density of 0.7 g/cm³. Yield strength and tensile strength of the SAS cover layer: DC01 (1.0330) steel to DIN EN 10130. *Material properties of sandwiches and aluminum foam depend strongly on the material density. **Material properties depend strongly on the geometry in question. Sources for the calculation: Tabellenbuch Metall, 43rd edition 2005; Fraunhofer Institute for Machine Tools and Forming Technology IWU. All values were determined analytically and serve as a guide; for specific applications the values must be determined individually.
Which material is the lightest?
Aluminum foam, by a clear margin. Its density is 0.5 to 0.8 g/cm³, against 2.7 g/cm³ for aluminum and 7.85 g/cm³ for steel; at densities from 0.5 g/cm³ it is even lighter than water and floats. On the reference plate of 1,000 × 1,000 × 10 mm³ that means 5 to 8 kg as aluminum foam, 27 kg as aluminum and 78.5 kg as steel. If you need cover layers for higher strength, the AAS 10-1-1 (1 mm aluminum cover layers, foam core 0.7 g/cm³) comes to about 11 kg and the SAS 10-1-1 (1 mm steel cover layers, foam core 0.7 g/cm³) to 21.3 kg.
How stiff is aluminum foam compared with steel and aluminum?
As a solid material, aluminum foam is considerably less stiff than sheet metal: according to the product data sheets, the Young's modulus of the foam core is 330 to 760 N/mm² depending on density, against 70 GPa for aluminum and 210 GPa for steel. The answer to this is the sandwich design: the foam forms the core, and the stiffness comes from the cover layers. With steel cover layers, as SAS 10-1-1 (1 mm steel cover layers, foam core 0.7 g/cm³), the plate weighs 21.3 kg instead of 78.5 kg for solid steel; with aluminum cover layers in the same build-up (AAS 10-1-1), about 11 kg.
Young's modulus of the foam core according to the AAS, SAS and Havel Lite® product data sheets, by density; the comparison values for sheet metal are analytically determined guide values according to Tabellenbuch Metall (43rd edition, 2005) and Fraunhofer IWU. Bending stiffness depends strongly on geometry.
Which material has the edge in fire protection?
Aluminum foam is non-combustible: the structure is purely metallic, with no adhesives or plastics. The product data sheet gives −20 to 200 °C without any impairment of its properties, and 600 °C as the maximum temperature. Because no adhesives are used, structures made of aluminum foam also add nothing to the fire load. For the sandwiches with steel or aluminum cover layers: Material testing of AAS and SAS to DIN EN 45545-2 resulted in classification as HL3; no certificate was applied for. That matters wherever fire protection standards determine the choice of material.
Recycling and durability in the material comparison
Aluminum foam is 100 % recyclable: no adhesives are used, and the material remains metal. That sets it apart from most other lightweight materials that combine low weight with stability: plastics, carbon-fiber-reinforced plastic (CFRP) and glass-fiber-reinforced plastic (GFRP) can hardly be recycled. The natural oxide layer also makes the metal durable.
What can aluminum foam do that steel or aluminum sheet cannot?
Aluminum foam brings functional properties that go beyond load-bearing alone. It absorbs pressure and impact loads and prevents material failure such as cracks and fractures, which increases safety and repairability. Sound waves are effectively damped as they pass through, with density and thickness determining the result. And it is among the best metallic heat conductors (12 to 36 W/mK), usable in cooling and heating systems alike. The material realizes its full potential when several of these properties come together in one application.
How aluminum foam differs from honeycomb, polymer foam and solid aluminum
Aluminum foam is not a honeycomb structure: its cellular build-up is closed-cell and consists of stochastically, that is irregularly, distributed cavities, modeled on coral and bone, not of regular honeycomb cells. Nor is it a polymer foam: the structure is purely metallic, with no adhesives or plastics. And it is not solid aluminum: gas inclusions turn a metal that is light to begin with into an even lighter material, from 0.5 g/cm³ instead of 2.7 g/cm³.
Weight and density
Which of the three materials is the lightest?
Also asked: How much does aluminum foam weigh compared with steel? · How big is the weight difference between foam, aluminum and steel?
Aluminum foam, and by a clear margin. Havel metal foam calculates the comparison on a plate of 1,000 × 1,000 × 10 mm³: in steel (S235JR) it weighs 78.5 kg, in aluminum (EN-AW 5754) 27 kg, and as aluminum foam 5 to 8 kg. The two sandwich designs lie in between, because they carry cover layers: about 11 kg as AAS 10-1-1 (1 mm aluminum cover layers, foam core 0.7 g/cm³), 21.3 kg as SAS 10-1-1 (1 mm steel cover layers, foam core 0.7 g/cm³). An AAS panel therefore weighs about one seventh of a steel plate of the same thickness. The reason lies in the density: the foam core has a density of 0.5 to 0.8 g/cm³, against 2.7 for aluminum and 7.85 for steel. All values are analytically determined guide values and depend strongly on the density chosen; for a specific application they are determined separately.
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Is aluminum foam lighter than water?
Also asked: Does aluminum foam float? · What is the density of aluminum foam?
Yes. Aluminum foam from Havel metal foam has a density of 0.5 to 0.8 g/cm³ across the regularly produced range, and so it is lighter than water over that whole range, while solid aluminum has 2.7 g/cm³ and steel 7.85 g/cm³. The cell structure makes this possible: the foam is closed-cell, the gas inclusions are stochastically distributed, and a metal that is light to begin with becomes a considerably lighter material. For design purposes the density is not a secondary value but the design parameter. Young's modulus, compressive strength and thermal conductivity depend on it, which is why it comes at the start of a design, not at the end: lower density for weight, higher density for strength. At Havel metal foam, the standard is 0.6 to 0.7 g/cm³, and regular production covers 0.5 to 0.8 g/cm³; higher densities by agreement and after prior testing.
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Stiffness and substitution
Does aluminum foam replace steel one for one?
Also asked: Can a steel plate simply be replaced with aluminum foam? · Is aluminum foam as stiff as steel?
No. Solid aluminum foam is considerably less stiff than sheet metal: the Havel metal foam product data sheets give a Young's modulus of 330 to 760 N/mm² for the foam core, depending on density grade, against 70 GPa for aluminum and 210 GPa for steel. If you replace a steel plate with solid foam, you lose stiffness. The material only becomes a substitute for steel as a sandwich, and the reason is the design: the foam forms the core and holds the cover layers apart, while the cover layers carry the bending load. That is why an SAS 10-1-1 (1 mm steel cover layers, foam core 0.7 g/cm³) comes to 21.3 kg instead of the 78.5 kg of a steel plate of the same thickness. Substitution here therefore does not mean swapping a sheet for a foam, but a plate for a build-up.
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How much weight does a sandwich save at equal bending stiffness?
Also asked: How much lighter is an aluminum foam sandwich than steel sheet? · What does the material deliver at equal stiffness?
At equal bending stiffness, aluminum foam sandwiches save around 65 % in weight compared with steel sheet. The comparison Havel metal foam calculates for this names both build-ups: 14 mm of aluminum foam with 1 mm steel cover layers, that is a 16 mm SAS, against a 10 mm steel plate. The decisive condition is that both build-ups have the same bending stiffness; without it, a weight figure between two materials is not comparable. The price for this is overall height: 16 mm instead of 10 mm. That is also the limitation that belongs with the comparison, because a sandwich's stiffness comes from its depth, and a sandwich needs space for it. Where the overall height is not constrained, the swap is attractive; where it is fixed, it is first and foremost a question of geometry.
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What does aluminum foam do that steel or aluminum sheet does not?
Also asked: Which additional functions does aluminum foam bring? · Why aluminum foam instead of sheet metal?
Aluminum foam brings functions that sheet metal does not have, and Havel metal foam uses the cell structure for them. The material absorbs pressure and impact loads and in doing so prevents cracks and fractures, which increases safety and repairability. Sound waves are damped as they pass through, with density and thickness determining the result. The foam conducts heat well, at 12 to 36 W/mK, and can therefore be used in cooling and heating systems alike. Two examples from the comparison with solid material: for the same crash function the foam comes to 1.3 kg/m against 1.75 kg/m for an aluminum profile, and as a heat sink in place of a finned die-cast part, a design proposal comes to about 30 g against about 60 g. The material realizes its potential when several of these properties come together in one application.
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Fire behavior and recycling
Which of the materials has the advantage in fire behavior?
Also asked: Is aluminum foam flammable? · How does aluminum foam behave in a fire compared with plastic?
Aluminum foam is non-combustible, and the reason is its build-up: Havel metal foam bonds the foam purely metallically, with no adhesives or plastics, which is why a structure made from it adds nothing to the fire load. Against the lightweight materials it otherwise competes with, this is the clearest difference: plastics, carbon-fiber-reinforced plastic (CFRP) and glass-fiber-reinforced plastic (GFRP) bring a fire load of their own. Against steel and aluminum, the difference lies not in flammability but in the temperature limit: the product data sheets give −20 to 200 °C without any impairment of its properties, and 600 °C as the maximum temperature. For the sandwiches, in addition: material testing of AAS and SAS to DIN EN 45545-2 resulted in classification as HL3; no certificate was applied for.
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How does aluminum foam perform on recycling?
Also asked: Is aluminum foam recyclable? · How sustainable is aluminum foam compared with fiber composites?
Aluminum foam is 100 % recyclable. Havel metal foam uses no adhesives, the material remains metal throughout and can be recycled as a single, unmixed material. Compared with the other materials that combine low weight with stability, the gap is widest here: plastics, CFRP and GFRP can hardly be recycled. Steel and aluminum are recyclable too, which is why the difference from these two lies not in recyclability itself, but in the fact that the lightweight design does not come at the expense of recyclability. The natural oxide layer also makes the metal durable. Corrosion protection is still needed, just as with steel.
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Distinctions and limits
Is aluminum foam the same as honeycomb?
Also asked: Is aluminum foam a honeycomb structure? · What is aluminum foam not?
No. The aluminum foam from Havel metal foam is closed-cell with a stochastic structure, so its cavities are irregularly distributed, modeled on coral and bone. A honeycomb structure, by contrast, is regular. The difference is not cosmetic: closed cells are the reason the material is non-combustible, can be bonded metallically and is insensitive to water. Two further distinctions belong here. Aluminum foam is not a polymer foam, because the structure is purely metallic, with no adhesives or plastics. And it is not solid aluminum: the gas inclusions turn a metal that is light to begin with into a material from 0.5 g/cm³ instead of 2.7 g/cm³. One exception in the portfolio is Havellux®, because this product is open-cell and intended for design and architecture.
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How does the material differ from other metal foams?
Also asked: What is the difference between closed-cell and open-cell metal foam? · How do the production processes for metal foam differ?
Aluminum foam from Havel metal foam is made by powder metallurgy and is closed-cell; melt-route foams are open-cell. The material values follow from this difference in process. The product data sheets give a compressive strength of 2.5 to 10 N/mm² for the core, depending on density grade, while the open-cell comparison products are at 1.0 to 1.8 MPa; for tensile strength it is 4 to 6.3 MPa against 0.5 to 1.2 MPa. The alloys differ as well, AlSi10 on one side and AA.1070 on the other. What goes beyond the material values also depends on the process: Havel metal foam produces sandwiches without adhesive bonding, 3D shaped elements, foamed tubes and profiles, 3D sandwiches with integrated cooling and heating pipes, and zinc foam, and the material is weldable.
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What are the material's limits in the comparison?
Also asked: What are the arguments against aluminum foam? · What are the drawbacks of an aluminum foam sandwich?
Aluminum foam has three limits that any sound comparison has to include. First, it needs corrosion protection, just as steel does; the natural oxide layer makes the metal durable but does not replace the protection. Second, a sandwich needs space: its stiffness comes from its overall height, and where that is fixed, swapping it for a sheet is first and foremost a question of geometry. Third, foam in the fastening area costs additional preparation time in manufacturing. There is also a limit in the data: no cost comparison against steel and aluminum is available, and a substitution decision is, in the end, a commercial one as well. The figures here are therefore technical comparisons and not a cost-effectiveness calculation. Havel metal foam assesses a specific case on request.
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