Properties of Aluminum Foam


(Acoustic Property)

Electromagnetic Shielding Property:

Electromagnetic waves can cause malfunctions in various electronic devices. Negative influence on human health is also being investigated. Electromagnetic wave shielding should be used to protect electronic devices and rooms interiors from electromagnetic waves. The material for this purpose should possess good electric conductivity to minimize the penetration of waves into the material and low magnetic permeability to convert magnetic energy into heat.

     

Shielding effectiveness(dB)Frequency

Closed-cell porosity:85%

Open cell porosity: 65%

Copper plate

300x300x7mm

300x300x905mm

500x500x10mm

110x110x6mm

2.6~3.95GHz

-73.2~ -77.9

-74~ -82.6

-74.4~ -92.1

-72.8~ -83.5

3.95~5.85GHz

-73.8~ -87.1

-69.2~ -87.1

-70.2~ -84.1

-72.8~ -98.1

8.2~12.4GHz

-69.2~ -74

-68.9~ -84.2

-70.4~ -79.3

-73.8~ -91.2

12~18GHz

-64.8~ -73

-63.3~ 7.02

-62.8~ -68.4

-63.8~ -67.8

Summary of Results:

· Aluminum foam possesses very good magnetic field shielding effectiveness.

· Electric shielding effectiveness of aluminum foam is comparable with the one of silicon steel for frequencies up to 10 MHz. Aluminum foam is superior for higher frequencies.

· Electromagnetic shield effectiveness of aluminum foam depends significantly on the frequency.

Conductivitythermal / electric)Property:

Only a small portion of Aluminum foam’s cross section is conductive. These are the pore walls with the conductivity value of the base alloy. The pore walls are continuously covered with non-conductive alumina. The main part of the cross section is formed by the pores filled with air which is non-conductive. Aluminum foam is therefore far less conductive than bulk aluminum.

Summary of Results / Thermal Conductivity:

· Thermal conductivity of aluminum is only 1/10 of that of base aluminum.

Summary of Results / Electrical Conductivity:

Electric conductivity decreases with density of aluminum foam.

Electric conductivity of aluminum foam is a non-linear function of density and obeys the power-law dependence with an exponent of 1.5.

Resonance Decrease Property:

Structural damping is the effect of internal friction within changing material vibration energy into heat. This reduces excessive noise and vibration by converting them into heat to be expelled into the surrounding area. Vibration energy in cellular structures is dissipated by the slight plastic deformation of the thin walls separating the pores. It can also be reduced by friction between the surfaces of cracks appearing in the pore walls.

Summary of Results:

· The loss factor of aluminum foam is significant higher than the loss factor of aluminum.

· The damping ability of aluminum foam allows reducing the noise induced by vibrations.

· Damping ability of aluminum foam depends insignificantly on resonant frequency.

Energy Absorption Property:

Impact absorbers protect passengers and fragile devices from the effects of sudden impact. This is achieved by converting the impact energy into plastic deformation energy, keeping the peak force acting on the protected object below the level which could cause damage. The material must also provide a long deformation path to sufficiently reduce the deceleration of the protected object.

The energy absorption properties can be adjusted through foam density respectively pore size and may be optimized through further heat treatment. Because of those excellent absorption properties aluminum foams are already used as serial part for crash absorption by leading automotive manufactures.

Summary of Results:

Aluminum’s cell walls start to buckle (wrought alloys) and fracture (cast alloys) at low stresses allowing for extensive compression with an adequate deceleration path.

Sound-proofing ability vs various frequencies of noise

Soundproofing effect measured by the 9th laboratory of acoustics institute of Chinese Academy of Sciences as follows:

Sound-proofing measurement result (db) for the aluminum foam sandwich (thickness 20mm)

Audio frequency

100Hz

315Hz

630Hz

1000Hz

2000Hz

3000Hz

4000Hz

Soundproofing volume

18.0

26.7

30.2

30.3

38.7

42.6

42.3

The sandwich board with about 20mm thickness can decrease the noise below international standard (60db) and improve the comfort degree in compartment with even reduction of more than 20db noise for low-frequency sound wave below 1000Hz.

Damping Performance Measurement Results

The 3560 portable vibrometer from Denmark B&K Corporation was adopted for measurement. Conclusion shows that the damping effect for vibration of the sandwich board is excellent. The damping coefficient can reach 3%~5% for vibration frequency below 36Hz. There is more than one order of magnitude of vibration decrease with adoption of ultra light porous aluminum foam sandwich board.

Vibration Damping Measurement Results 

Audio frequency

63.75Hz

71.25Hz

97.5Hz

362.5Hz

Sound-proofing volume, %

3.34

5.43

5.45

4.51

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