Method for foaming metal in a liquid bath

Abstract

The invention relates to a method for producing a metal foam of at least one first metal that contains the main constituent Mg, Al, Pb, Au, Zn, Ti or Fe in a quantity of at least approximately 80 wt. % in relation to the quantity of the at least one first metal, said method comprising the following steps: (I) providing a semi-finished product comprising a foamable mixture that comprises the at least one first metal and at least one foaming agent, (II) submerging the semi-finished product in a heatable bath comprising a liquid, and (III) heating the semi-finished product in the bath in order to foam the foamable mixture by removing gas from the at least one foaming agent for forming the metal foam. The invention also relates to a metal foam, to a composite material that can be obtained by the method, and to a component comprising the metal foam and/or the composite material.

Claims

1. Method for producing a metal foam of at least one first metal that contains a main constituent of Mg, Al, Pb, Au, Zn, Ti or Fe in a quantity of at least approximately 80 wt. % in relation to the quantity of the at least one first metal, said method comprising the following steps: (I) providing a semi-finished product comprising a foamable mixture that comprises the at least one first metal and at least one blowing agent, (II) submerging the semi-finished product in a heatable bath comprising a liquid wherein the liquid of the heatable bath comprises at least one molten salt or solid particle, and (III) heating the semi-finished product in the bath in order to foam the foamable mixture by removing gas from the at least one blowing agent for forming the metal foam.

2. Method according to claim 1, wherein the semi-finished product comprises at least one first region, which is formed from the foamable mixture, and at least one second region, which is formed from at least one second metal in the form of non-foamable full material, for producing a composite material, the composite material comprising at least one first region, which is formed from the metal foam of the at least one first metal, and at least one second region, which is formed from at least one second metal in the form of non-foamable full material.

3. Method according to claim 2, wherein the at least one second metal contains a main constituent of Mg, Al, Pb, Au, Zn, Ti or Fe in a quantity of at least approximately 80 wt. % in relation to the quantity of the at least one second metal.

4. Method according to claim 3, wherein the at least one first metal and the at least one second metal have the same main constituent Mg, Al, Pb, Au, Zn, Ti or Fe.

5. Method according to claim 2, wherein the at least one second metal (a) has a solidus temperature that is at least 5° C. higher than the liquidus temperature of the foamable mixture; and/or (b) has fewer alloy constituents than the at least one first metal or has at least one identical alloy constituent having a lower mass proportion in the alloy than for the at least one first metal.

6. Method according to claim 2, wherein the at least one second region is formed as a layer on at least part of the surface of the at least one first region.

7. Method according to claim 6, wherein (a) in the composite material the at least one first region is formed as a foamed core, and (b) in the semi-finished product for producing this composite material the at least one first region is formed as a foamable core.

8. Method according to claim 2, wherein the gas evolution temperature of the at least one blowing agent is below the solidus temperature of the at least one second metal.

9. Method according to claim 2, wherein the heating in step (III) takes place to a foaming temperature that, within the foamable mixture, is less than the solidus temperature of the at least one second metal.

10. Method according to 1, wherein the gas evolution temperature of the at least one blowing agent (a) is equal to the solidus temperature of the at least one first metal or (b) below the solidus temperature of the at least one first metal, but not more than approximately 90° C. below the solidus temperature of the at least one first metal.

11. Method according to claim 1, wherein the at least one blowing agent is selected from the group consisting of metal hydrides and metal carbonates.

12. Method according to claim 1, wherein the heating in step (III) of the method also takes place to a foaming temperature that, within the foamable mixture, is (a) at least as high as the gas evolution temperature of the at least one blowing agent and/or (b) at least as high as the solidus temperature of the foamable mixture.

13. Method according to claim 1, additionally comprising the step of (IV) preheating by heating the semi-finished product of step (I) to a temperature approximately 50° C. to approximately 100° C. below the foaming temperature, step (IV) being performed temporally before step (II) and/or step (III).

14. Method according to claim 1, wherein the heating in step (III) takes place at a heating rate of approximately 0.5 K/s to approximately 50 K/s.

15. Method according to claim 1, wherein the liquid of the heatable bath has (a) a specific heat capacity of approximately 1000 J/(kg.Math.K) to approximately 2000 J/(kg.Math.K), and/or (b) a thermal conductivity of approximately 0.1 W/(m.Math.K) to approximately 1 W/(m.Math.K).

16. Method according to claim 1, wherein the solid particles have a particle size in a range of approximately 10 μm to approximately 200 μm.

17. Method according to claim 1, wherein solid particles of aluminum oxide are used as the solid particles.

18. Method according to claim 1, wherein, while using solid particles, a fluidized bed furnace is used.

19. Method according to claim 1, wherein in step (III) a substantially closed-pore metal foam is formed.

20. Method according to claim 1, wherein the porosity of the metal foam formed in step (III) is approximately 60% to approximately 92%.

21. Method according to claim 1, additionally comprising the step of shaping the semi-finished product provided in step (I) into a shaped part, the shaped part thus obtained being heated instead of the semi-finished product in step (III).

Description

(1) The invention is explained in greater detail with reference to FIG. 1.

(2) FIG. 1 shows a composite material according to the invention in cross section as a metal foam sandwich that has been produced in a salt bath in accordance with Example 1.

(3) Example 1

(4) A semi-finished product, consisting of two solid cover layers and a foamable core that contained a foamable mixture, the metal or the metal components of which in each case consisted of an aluminum alloy as set out in the table below, was dipped in a salt bath at a temperature of 550° C. to 650° C. and foamed therein. As a result of the high heat capacity and thermal conductivity of the salt and the excellent thermal contact in the salt bath over the entire surface of the semi-finished product by comparison with conventional heating methods when aluminum is foamed, the semi-finished product was brought very homogeneously to the foaming temperature of 550° C. to 650° C.; in other words, all regions of the semi-finished product reached the sought foaming temperature simultaneously or virtually simultaneously. After the solidus temperature was exceeded, the foamable core started to expand uniformly and formed a good pore distribution (see FIG. 1). In this context, the heating rates of the foaming were between 0.5 K/s and 50 K/s, irrespective of the material thickness. As a result of the foaming, the density of the semi-finished product fell below the density of the salt bath, causing the metal foam sandwich to swell up and the end of the foaming process to be easily detectable.

(5) The method was accordingly also carried out using a semi-finished product consisting only of a pressed foamable mixture without cover layers.

(6) TABLE-US-00002 Alloy in Blowing agent.sup.1 in the foamable the foamable Alloy of the Example mixture mixture cover layers 1.1 AlSi8Mg4 TiH.sub.2 (1.0 wt. %) Al 6082 1.2 AlSi8Mg4 TiH.sub.2 (0.5 wt. %) Al 5754 1.3 AlSi8Mg4 TiH.sub.2 (0.6 wt. %) Al 5005 1.4 AlSi8Mg4 TiH.sub.2 (0.6 wt. %) Al 6016 1.5 AlSi7 TiH.sub.2 (1.2 wt. %) Al 3103 1.6 AlSi6Mg7.5 TiH.sub.2 (0.8 wt. %) Al 6060 1.7 AlSi4Mg7.5 TiH.sub.2 (0.6 wt. %) without cover layers 1.8 AlSi6Mg3 TiH.sub.2 (0.6 wt. %) without cover layers .sup.1The specification of the quantity of blowing agent in % by weight (wt. %) is based on the total quantity of the foamable mixture. The same method was also carried out with the following blowing agents instead of TiH2 in the amounts set out above: ZrH.sub.2, HfH.sub.2, MgH.sub.2, CaH.sub.2, SrH.sub.2, LiBH.sub.4 and LiAlH.sub.4, as well as each of the combinations of TiH.sub.2 with LiBH.sub.4 and TiH.sub.2 with LiAlH.sub.4.

(7) Example 2

(8) The method was carried out in accordance with Example 1, but with the salt bath having a temperature of 400° C. to 500° C. and the foam temperature being 380° C. to 420° C.

(9) TABLE-US-00003 Alloy in Blowing agent.sup.1 in the foamable the foamable Alloy of the Example mixture mixture cover layers 2.1 ZnTi2 MgH.sub.2 (0.5 wt. %) Al 6082 2.2 ZnTi2 MgH.sub.2 (0.6 wt. %) Al 6082 2.3 ZnTi2 MgH.sub.2 (0.8 wt. %) Al 6082 2.4 ZnTi2 MgH.sub.2 (1.0 wt. %) Al 6082 2.5 ZnTi2 MgH.sub.2 (1.2 wt. %) Al 6082 2.6 ZnTi2 MgH.sub.2 (0.6 wt. %) without cover layers 2.7 ZnCu8 MgH.sub.2 (0.6 wt. %) without cover layers .sup.1The specification of the quantity of blowing agent in % by weight (wt. %) is based on the total quantity of the foamable mixture. The same method was also carried out with TiH.sub.2 as a blowing agent instead of MgH.sub.2 in the amounts set out above.

(10) Example 3

(11) The method was carried out in accordance with Example 1, but with the salt bath having a temperature of 300° C. to 400° C. and the foam temperature being 310° C. to 380° C.

(12) TABLE-US-00004 Alloy in Blowing agent.sup.1 in the foamable the foamable Alloy of the Example mixture mixture cover layers 3.1 PbCu1 ZrH.sub.2 (0.5 wt. %) Al 6082 3.2 PbCu1 ZrH.sub.2 (0.6 wt. %) Al 6082 3.3 PbCu1 ZrH.sub.2 (0.8 wt. %) Al 6082 3.4 PbCu1 ZrH.sub.2 (1.0 wt. %) Al 6082 3.5 PbCu1 ZrH.sub.2 (1.2 wt. %) Al 6082 3.6 PbCu1 ZrH.sub.2 (0.8 wt. %) without cover layers 3.7 PbZn5 ZrH.sub.2 (0.8 wt. %) without cover layers .sup.1The specification of the quantity of blowing agent in % by weight (wt. %) is based on the total quantity of the foamable mixture. The same method was also carried out with TiH.sub.2 as a blowing agent instead of ZrH.sub.2 in the amounts set out above.

(13) Example 4

(14) The method was carried out in accordance with Example 1, but with the salt bath having a temperature of 550° C. to 650° C. and the foam temperature being 580° C. to 630° C.

(15) TABLE-US-00005 Alloy in Blowing agent.sup.1 in the foamable the foamable Alloy of the Example mixture mixture cover layers 4.1 AZ 31 TiH.sub.2 Al 6082 (Mg96Al3Zn) (0.5 wt. %) 4.2 AZ 31 TiH.sub.2 Al 6082 (Mg96Al3Zn) (0.6 wt. %) 4.3 AZ 31 TiH.sub.2 Al 6082 (Mg96Al3Zn) (0.8 wt. %) 4.4 AZ 31 TiH.sub.2 Al 6082 (Mg96Al3Zn) (1.0 wt. %) 4.5 AZ 31 TiH.sub.2 Al 6082 (Mg96Al3Zn) (1.2 wt. %) 4.6 AZ 31 TiH.sub.2 without cover layers (Mg96Al3Zn) (0.6 wt. %) 4.7 AZ 91 TiH.sub.2 without cover layers (Mg90Al9Zn) (0.6 wt. %) .sup.1The specification of the quantity of blowing agent in % by weight (wt. %) is based on the total quantity of the foamable mixture.

(16) Example 5

(17) The method was carried out in accordance with Example 1, but with the salt bath having a temperature of 1200° C. to 1450° C. and the foam temperature being 1380° C. to 1420° C.

(18) TABLE-US-00006 Alloy in Blowing agent.sup.1 in the foamable the foamable Alloy of the Example mixture mixture cover layers 5.1 Steel 1.4301 MgCO.sub.3 TiAl2 (0.5 wt. %) 5.2 Steel 1.4301 MgCO.sub.3 TiAl2 (0.6 wt. %) 5.3 Steel 1.4301 MgCO.sub.3 TiAl2 (0.8 wt. %) 5.4 Steel 1.4301 MgCO.sub.3 TiAl2 (1.0 wt. %) 5.5 Steel 1.4301 MgCO.sub.3 TiAl2 (1.2 wt. %) 5.6 Steel 1.4301 MgCO.sub.3 without cover layers (1.0 wt. %) 5.7 ST37 MgCO.sub.3 without cover layers (1.0 wt. %) .sup.1The specification of the quantity of blowing agent in % by weight (wt. %) is based on the total quantity of the foamable mixture.

(19) Example 6

(20) The method was carried out in accordance with Example 1, but with the salt bath having a temperature of 1300° C. to 1650° C. and the foam temperature being 1500° C. to 1680° C.

(21) TABLE-US-00007 Alloy in the Blowing agent.sup.1 in the Example foamable mixture foamable mixture Alloy of the cover layers 6.1 Ti—6Al—2Sn—4Zr—6Mo SrCO.sub.3 (0.5 wt. %) Ti—5Al—2Sn—2Zr—4Mo—4Cr or Ti 6.2 Ti—6Al—2Sn—4Zr—6Mo SrCO.sub.3 (0.6 wt. %) Ti—5Al—2Sn—2Zr—4Mo—4Cr or Ti 6.3 Ti—6Al—2Sn—4Zr—6Mo SrCO.sub.3 (0.8 wt. %) Ti—5Al—2Sn—2Zr—4Mo—4Cr or Ti 6.4 Ti—6Al—2Sn—4Zr—6Mo SrCO.sub.3 (1.0 wt. %) Ti—5Al—2Sn—2Zr—4Mo—4Cr or Ti 6.5 Ti—6Al—2Sn—4Zr—6Mo SrCO.sub.3 (1.2 wt. %) Ti—5Al—2Sn—2Zr—4Mo—4Cr or Ti 6.6 Ti—6Al—2Sn—4Zr—6Mo SrCO.sub.3 (1.0 wt. %) without cover layers 6.7 Ti—5Al—2Sn—2Zr—4Mo—4Cr SrCO.sub.3 (1.0 wt. %) without cover layers .sup.1The specification of the quantity of blowing agent in % by weight (wt. %) is based on the total quantity of the foamable mixture.

(22) Example 7

(23) The method was carried out in accordance with Example 1, but with the salt bath having a temperature of 900° C. to 1150° C. and the foam temperature being 980° C. to 1100° C.

(24) TABLE-US-00008 Alloy in Blowing agent.sup.1 in the foamable the foamable Alloy of the Example mixture mixture cover layers 7.1 750 Au SrCO.sub.3 (0.5 wt. %) Pt 7.2 750 Au SrCO.sub.3 (0.6 wt. %) Pt 7.3 750 Au SrCO.sub.3 (0.8 wt. %) Pt or Ti 7.4 750 Au SrCO.sub.3 (1.0 wt. %) Pt or Ti 7.5 750 Au SrCO.sub.3 (1.2 wt. %) Pt or Ti 7.6 750 Au SrCO.sub.3 (1.0 wt. %) without cover layers 7.7 585 Au SrCO.sub.3 (1.0 wt. %) without cover layers .sup.1The specification of the quantity of blowing agent in % by weight (wt. %) is based on the total quantity of the foamable mixture.

(25) Example 8

(26) The method was carried out in accordance with Example 1, but with, instead of a salt bath, a fluidized bed furnace being used having aluminum oxide granulate as a solid particle bath having a particle size in a range of approximately 80 μm to approximately 100 μm. The temperature for the heating after step (III) was 600° C. and the dwell time in the fluidized bed furnace was 3 min. AlSi8Mg4 was used as the alloy and 0.8 wt. % TiH.sub.2, in relation to the total quantity of the foamable mixture, was used as the blowing agent. Before foaming, the semi-finished product was prewarmed/heated over 15 min. in a sand bath at 500° C. The foaming took place by submerging in the heated solid particle bath. The bath for prewarming/preheating and for foaming may also be identical. The obtained composite material was formed closed-pore and had a highly homogeneous metal foam between the two cover layers.