EP2427284B1 - Powder-metallurgical method for producing metal foam - Google Patents

Description

The invention relates to a powder metallurgical process for the production of aluminum-based metal foam.

Process for producing metal foams with blowing agent or gas-releasing agent (eg. US 3,087,807 ZrH _1.01 as a gas-releasing agent; US 2,935,396 CdCO ₃ or MgCO ₃ as a gas-releasing agent; US 2,983,597 - TiH ₂ or ZrH ₂ as blowing agent) have long been known.

Powder metallurgical processes for the production of metal foams have also been developed for years and the metal foams produced have been investigated for their properties.

In general, such a powder metallurgical process comprises the following process steps: mixing at least one metal powder and one blowing agent powder, then compacting to form a dense, foamable semi-finished product. If this semifinished product is heated above the melting point, it expands and the metal is converted into a semi-liquid, viscous state, at the same time releasing gas from the decomposing propellant and foaming the semifinished product.

In DE 101 15 230 A1 a powder metallurgical process is described in which as blowing agent-containing powder, a metal compound is selected, the metal component consists exclusively of one or more metals to be foamed powdered metallic material to the metal component to change the alloy composition to a small extent and to cause no metallic impurities. Preferred propellants are salts which are selected from acetates, hydrates, hydroxides, hydrides and carbonates or mixed salts thereof and which are particularly efficient gas formers which, when decomposed, preferably form hydrogen, carbon dioxide, carbon monoxide, water and / or methane.

In recent years, powder metallurgical processes for producing metal foams have also been developed without the use of a blowing agent. For example, in DE 10 2005 037 305 A1 described a method in which the metal powder was first pressed under mechanical pressure and a temperature of up to 400 ° C to a dimensionally stable semi-finished, this then in a pressure-tight chamber sealed at a selected initial pressure of up to 5 MPa on the melt or the solidus temperature of the metal powder is heated. After reaching this temperature, the pressure is reduced defined, the semi-finished foams up, the resulting metal foam solidifies during the final lowering of the temperature. This method is relatively expensive due to the necessity of pressure-tight containers.

An in US 4,283,465 A The method described relates to the production of a porous sintered body. In this method, a first component of an Al alloy powder with 0.1% Mg, 0.1% Si, 1% Cu and 0.2% Mn is a second component of an Al-Mg (20%) powder or Granules mixed. The admixed component forms the second melt fraction for the liquid phase sintering process of the two components following the mixing step. The applied pressure of less than 80 Pa is used to shape the sintered body and reduce the resulting sintering cavities, which are all connected. A gas release does not take place here.

Therefore, it is an object of the invention to provide a further powder metallurgical process for the production of aluminum-based metal foam, which is less expensive and less expensive and only with alloy-inherent components compared to the prior art.

The object is achieved by a method having the features of claim 1.

The result surprisingly found in experiments to change an Al alloy by adding Al (1-x) Mg (x) powder found that the Al (1-x) Mg (x) powder and even pure Mg Powder contains so much hydrogen that it is one for the foaming process Sufficient amount of hydrogen at the temperature increase gives off. Thus, this Al (1-x) Mg (x) powder acts both as an alloying ingredient - in the inventive method to a much greater extent than the prior art after mentioned - and as a gas generator. The supply of a special propellant, which necessarily contains alien components, is therefore no longer necessary.

According to the invention, the powder metallurgical process for the production of aluminum-based metal foam comprises at least the process steps: mixing a metal powder of at least aluminum with Al (1-x) Mg (x) with 10 mass% ≦ x ≦ 100 mass% as gas generator in the form of metal powder in a concentration of 4 to 50 mass%; then compacting the metal powder mixture; then heating the compact at atmospheric pressure to a temperature above the melting point of the metal matrix to produce a liquid metal foam and then cooling the resulting metal foam at a temperature below the solidus temperature of the metal matrix.

If x <100 mass%, pre-alloyed Al-Mg metal powder is used.

The compacting of the metal powder mixture takes place for example by means of uniaxial compaction or by extrusion.

In embodiments of the invention it is envisaged that for the production of Al-based metal foam Al powder in a concentration of 50 to 96 mass% is mixed with Al (1-x) Mg (x) as the remainder.

To reduce the melting temperature of an Al-based alloy, instead of the Al powder, up to 40 mass% of Cu powder or up to 15 mass% of Si powder or up to 40 mass% of Zn powder may optionally be used. Even small additions of up to 5 mass% of Sn or Sb or Mn or Ni powders to the metal powder mixture instead of the Al powder cause a reduction of the melting temperature.

Further embodiments relate to the compaction of the powder mixture, which is carried out at a temperature in the range of 200 ° C ≤ T ≤ 450 ° C and at a pressure in the range of 200 MPa ≤ p ≤ 500 MPa, and the temperature for the foaming process for an Al -based metal foam is set between 450 and 650 ° C.

The Al (1-x) Mg (x) alloy having 10 mass% ≦ x ≦ 100 mass% can be used both as a gas generator and as an alloying ingredient in the production of metal foams.

The hitherto undesirable in the foaming process hydrogen, which was caused by the addition of pre-alloyed Al (1-x) Mg (x) powder for-changing the alloy during the temperature increase, is deliberately exploited in the inventive method as a gas forming agent, so that no additional propellant must be added. Thus, in the process according to the invention for the production of metal foams, no alien components are used.

With the method according to the invention, metal foams having a homogeneous and stable foam structure, which has small pores with an average diameter between 0.05 and 2 mm, could be produced. The pores are also not interconnected, which could not yet be achieved with the prior art according to known powder metallurgy processes. Another advantage of the invention is - as already mentioned - is that with the admixture of Al (1-x) Mg (x) powder with 10 mass% ≤ x ≤ 100 mass% of the melting point of the Al-based alloy was lowered.

The invention will now be explained in more detail in exemplary embodiments with reference to FIGS.

Fig. 1:

Aufnahme eines Al-basierten Metallschaums gemäß Stand der Technik-Verfahren hergestellt;

Fig. 2:

Aufnahme eines Al-basierten Metallschaums gemäß erfindungsgemäßem Verfahren hergestellt;

Fig. 3:

Mikroskopaufnahme eines Al-basierten Metallschaums hergestellt mit erfindungsgemäßem Verfahren;

Fig. 4:

Spannungs-Druckverhalten des Al-basierten Metallschaums gemäß Fig. 2 und 3.

Show

Fig. 1:

Recording of an Al-based metal foam prepared according to prior art methods;

Fig. 2:

Recording an Al-based metal foam prepared according to the inventive method;

3:

Microscope image of an Al-based metal foam prepared by the method according to the invention;

4:

Stress-pressure behavior of the Al-based metal foam according to Fig. 2 and 3 ,

Fig. 1 and Fig. 2 show in each case a comparison of an Al-based metal foam prepared according to a known powder metallurgy process with propellant ( Fig. 1 ) and without propellant ( Fig. 2 ), ie produced according to the inventive method. Clearly visible are the significantly larger pores in the propellant produced metal foam.

Fig. 3 shows a microscope image of the foam structure of an Al-based metal foam produced by the process according to the invention, now in a higher magnification than in Fig. 1 , This metal foam is produced as follows: 60% by weight of Al powder and 30% by weight of AlMg50 powder and 10% by weight of Cu powder are used to produce the powder mixture. The Cu powder was added to lower the melting point of the alloy. The compaction takes place at 400 ° C and a pressure of 300 MPa. For foaming the compacted sample, a temperature of 600 ° C is set. The Al-based metal foam thus prepared has a density of 0.6 gcm ^-3 and pores having an average diameter of 800 μm.

In Fig. 4 the curve for the stress-strain behavior of a metal foam with the composition AlMg15Cu10 is shown, which has a density of 0.72 gcm ^-3 and an average diameter of the pores of 1 mm. Investigations of the metal foam produced by the process according to the invention have shown that its compressive strength and rigidity are at least as good as those of other standard foams.

Claims (11)

1. A powder-metallurgical method for producing aluminium-based metal foam, at least comprising the method steps of

   - mixing a metal powder formed of at least aluminium with Al(1- x)Mg(x) where 10 mass % ≤ x ≤ 100 mass % as gas producer in the form of metal powder in a concentration from 4 to 50 mass %;

   - then compacting the metal powder mixture,

   - then heating the compact at atmospheric pressure to a temperature above the melting point of the metal matrix in order to produce a liquid metal foam,

   - lastly cooling the produced microcellular metal foam at a temperature below the solidus temperature of the metal matrix.
2. The method according to Claim 1, characterised in that Al(1-x)Mg(x) with 40 mass % ≤ x ≤ 60 mass %, preferably AlMg50, is used.
3. The method according to Claim 1, characterised in that pre-alloyed metal powder is used for x < 100 mass %.
4. The method according to Claim 1, characterised in that Zn is admixed to the metal powder.
5. The method according to Claim 4, characterised in that for the production of Al-based metal foam, Al powder is mixed in a concentration of 50 to 96 mass % with Al(1-x)Mg(x) forming the rest.
6. The method according to claim 4 and 5, characterised in that up to 40 mass % Cu powder is used selectively instead of the Al powder forming the basis of the metal foam.
7. The method according to claim 4 and 5, characterised in that up to 15 mass % Si powder is used selectively instead of the Al powder forming the basis of the metal foam.
8. The method according to claim 4 and 5, characterised in that up to 40 mass % Zn powder is used selectively instead of the Al powder forming the basis of the metal foam.
9. The method according to claim 4 and 5, characterised in that up to 5 mass % Sn or Sb or Mn or Ni powder is used selectively instead of the Al powder forming the basis of the metal foam.
10. The method according to Claim 1, characterised in that the compaction of the powder mixture is carried out at a temperature in the range of 200 °C ≤ T 450 °C and at a pressure in the range of 200 MPa ≤ p ≤ 500 MPa.
11. The method according to Claim 1 and 4, characterised in that the compact for an Al-based metal foam is foamed at a temperature of 450 °C ≤ T ≤ 650 °C.

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