Method for producing a semi-finished product for a composite matertal

Abstract

The invention relates to a method for producing a semi-finished product comprising a foamable core comprising a foamable mixture that comprises at least one first metal having an aluminum content of at least approximately 80 wt. %, in relation to the quantity of the at least one first metal, and at least one foaming agent, wherein a layer of at least one second metal in the form of a non-foamable solid material and with an aluminum content of at least approximately 80 wt. %, in relation to the quantity of the at least one second metal, is respectively applied to at least one first and second surface of the core. The invention also relates to a corresponding semi-finished product and to the use of such a semi-finished product for foaming a metal.

Claims

1. A method for producing a semi-finished product comprising a foamable core which comprises a foamable mixture comprising at least one first metal having an aluminum content of at least approximately 80 wt. %, in relation to the quantity of the at least one first metal, and at least one foaming agent, wherein a layer of at least one second metal in the form of non-foamable solid material and having an aluminum content of at least approximately 80 wt. %, in relation to the quantity of the at least one second metal, is applied to each of at least one first and one second surface of the core, the method comprising the steps of (I) providing a container comprising a layer of the at least one second metal on the at least one first and second surfaces of the container, (II) providing a powder comprising powder particles of the at least one first metal, (III) providing a powder comprising powder particles of the at least one foaming agent, and (IV) filling the container with the powders provided in steps (II) and (III) to form the foamable core, wherein the powders provided in steps (II) and (III) are mixed to form the foamable mixture additionally comprising the steps of: (VI) first metallurgically bonding the powder particles of the foamable mixture to each other and/or to the one layer of the second metal on each of the first and second surfaces of the core to form the foamable core according to step (IV), wherein, in step (VI), either pre-compression of the foamable mixture together with the container is carried out under application of pressure at a temperature of the foamable mixture and of the container of from approximately 65% to approximately 90% of the solidus temperature of the foamable mixture or the foamable mixture and the container are heated to approximately 70% to approximately 90% of the solidus temperature of the foamable mixture, wherein expansion of the container is substantially prevented; and additionally comprising the step of (VII) second metallurgical bonding of the foamable core obtained in step (VI) to the layers of the at least one second metal on the first and second surfaces of the container, wherein the second metallurgical bonding is carried out by rolling under the action of pressure on the container, wherein the temperature of the container is from approximately 400° C. to approximately 520° C., in each case at a temperature of the container below the outgassing temperature of the at least one foaming agent.

2. The method according to claim 1, wherein the at least one second metal (a) has a solidus temperature which is at least approximately 5° C. higher than the liquidus temperature of the foamable mixture; and/or (b) has fewer alloying constituents than the at least one first metal or has at least one identical alloying constituent with a lower mass fraction in the alloy than the at least one first metal.

3. The method according to claim 1, wherein (a) the at least one first metal is selected from the group consisting of aluminum, higher-strength aluminum alloys selected from the group consisting of aluminum-magnesium-silicon alloys (6000 series) and aluminum-zinc alloys (7000 series), and higher-strength aluminum alloys having a melting point of approximately 480° C. to approximately 580° C.; and/or (b) the at least one second metal is selected from the group consisting of aluminum and higher-strength aluminum alloys selected from the group consisting of aluminum-magnesium alloys (5000 series), aluminum-magnesium-silicon alloys (6000 series) and aluminum-zinc alloys (7000 series).

4. The method according to claim 1, wherein the mixing of the powders provided in steps (II) and (III) to form the foamable mixture is carried out before or during step (IV).

5. The method according to claim 1, wherein the outgassing temperature of the at least one foaming agent is equal to the solidus temperature of the at least one first metal or is below the solidus temperature of the at least one first metal but is not more than approximately 90° C. below the solidus temperature of the at least one first metal and is less than the solidus temperature of the at least one second metal.

6. The method according to claim 1, wherein the at least one foaming agent comprises at least one metal hydride.

7. The method according to claim 6, wherein the at least one foaming agent additionally comprises at least one oxide and/or at least one oxyhydride of the metal of the particular metal hydride.

8. The method according to claim 7, wherein at least one foaming agent is TiH2 and the at least one (a) oxide is an oxide of the formula TivOw, wherein v is from approximately 1 to approximately 2 and w is from approximately 1 to approximately 2, and/or (b) oxyhydride is an oxyhydride of the formula TiHxOy and x is from approximately 1.82 to approximately 1.99 and y is from approximately 0.1 to approximately 0.3.

9. The method according to claim 1, wherein the quantity of the at least one foaming agent is from approximately 0.1 wt. % to approximately 1.9 wt. % in relation to the quantity of the at least one first metal.

10. The method according to claim 7, wherein the quantity of the at least one oxide and/or at least one oxyhydride is from approximately 0.01 wt. % to approximately 30 wt. % in relation to the total quantity of the at least one foaming agent.

11. The method according to claim 1, wherein (a) the at least one first surface of the container and the at least one second surface of the container (a.1) are arranged opposite each other, and/or (a.2) are substantially plane-parallel; and/or (b) the foamable core is formed as a layer between the at least one first and second surface of the container.

12. The method according to claim 1, additionally comprising the step of (V) drying (V.1) of the powder of the at least one first metal before step (IV) and/or of the powder of the at least one foaming agent before step (IV), or (V.2) of the foamable mixture before step (IV), or (V.3) of the foamable mixture and the container after step (IV).

13. The method according to claim 1, wherein the temperature of the container at the beginning of the particular method step is from approximately 400° C. to approximately 540° C.

14. A semi-finished product formed by a method as defined in claim 1.

15. A container for carrying out the method according to claim 1, the container having a first and a second surface forming a base and a lid, and side walls, wherein at least one side wall has an inward buckling in the direction of a foamable mixture.

Description

(1) The invention shall be further explained by means of the drawings or figures listed and described below, from which further advantageous embodiments of the invention may be deduced, without, however, necessarily limiting the invention or individual features of the invention. Rather, features described there may be combined with each other and with the features described above to form further embodiments of the invention.

(2) FIG. 1 is an illustration of the container and shows the box-shaped container lower part, consisting of base (3) and side walls (1), and the lid (3). Base and lid (3) form the layers or cover layers or top layers made of the at least one second metal (cover layer material), which later cover the foamable core. The filling holes or openings (2) are used for filling the foamable mixture and, if necessary, escape of gases during the first and/or second metallurgical bonding during steps (VI) and (VII).

(3) FIG. 2 is a representation of the container in an exploded drawing and also shows the side walls (1), which have a buckling of approximately 175°, filling holes or openings (2) and base and lid (3) as (subsequent) top layers or cover layers.

(4) The invention will be explained in more detail on the basis of the exemplary embodiments described below, without necessarily limiting the invention or individual features of the invention.

EXAMPLE 1

(5) The following method steps were used to produce the foamable semi-finished product for the production of aluminum foam sandwich structures. First, the powder mixture (foamable mixture) was produced. For this purpose, 0.4 to 1.0 wt. % TiH.sub.2 in powder form (weight % in relation to the aluminum alloy) was mixed with a powder of the aluminum alloy AISi8Mg4 as the first metal. This powder mixture was then filled into an aluminum container of the alloy Al 6082 (AISi1MgMn) as the second metal, in which two opposite walls formed the later cover layers of the triple-layer primary material (semi-finished product), which foams to form a sandwich structure (composite material). The aluminum alloy of the container was selected here so that it had a solidus temperature that was higher than the liquidus temperature of the powder mixture (foamable mixture). After the container was completely filled with the powder mixture, the powder mixture was dried. The powder was heated up to 300° C. and the resulting moisture was removed. The container was then heated to approximately 80% of the solidus temperature of the powder mixture or of the at least one first metal and kept at a temperature of 455° C. for 6 to 24 hours to achieve a first metallurgical bond, and expansion of the container was suppressed. In the following rolling process, the container was hot rolled at a pressure of approximately 6000t in the roll gap at a temperature of approximately 475° C. to obtain a second metallurgical bond. This was followed, if necessary, by another cold rolling process to achieve sheet thicknesses below 9 mm. By means of the rolling process the second metallurgical bond between powder and cover layer was achieved and the powder was furthermore compacted to 98% to 100% of the density of the solid material. The resulting triple-layer sheets were then finished and fed to the foaming process. The above method was also carried out with the following aluminum alloys for the metal in the powder mixture and the container as well as the following foaming agents in the indicated quantities:

(6) TABLE-US-00001 Alloy of the Alloy of metal of the the metal of Example powder mixture Foaming agent.sup.1 the container 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 AlSi6Cu7.5 TiH.sub.2 (0.8 wt. %) Al 6060 .sup.1The specification of the quantity of foaming agent in weight % (wt. %) is based on the total quantity of the foamable mixture/powder blend. The same method was also carried out with the following foaming agents instead of TiH.sub.2: 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 combinations of TiH.sub.2 with LiBH.sub.4 and TiH.sub.2 with LiAlH.sub.4.

EXAMPLE 2

(7) The following method steps were used to produce the foamable semi-finished product for the production of aluminum foam sandwich structures. First, the powder mixture (foamable mixture) was produced. For this purpose, 0.4 to 1.0 wt. % TiH.sub.2 in powder form (weight % in relation to the aluminum alloy) was mixed with a powder of the aluminum alloy AlSi8Mg4. This powder mixture was then filled into an aluminum vessel (aluminum container) of the alloy AL 6082 (AlSi1Mg—Mn), in which two opposite walls formed the later cover layers of the triple-layer pre-material (semi-finished product), which foams to form a sandwich structure. The alloy of the aluminum container was selected so that it had a solidus temperature that was higher than the liquidus temperature of the powder mixture (foamable mixture). After the container was completely filled with the powder mixture, the powder mixture was dried. The powder was heated up to 300° C. and the resulting moisture was removed. The container was then pre-compressed for the first time at a pressure of 0.2 MPa using two plane-parallel tools in a pressing process over a period of approximately 28 hours. The powder was pre-compressed at 400° C. to 460° C. The pre-compression produced a stable rolling ingot. Furthermore, the powder particles were partially bonded to the cover layers in a first metallurgical bond. In the following rolling process for the second pre-compression, the vessel was hot rolled at a temperature of approximately 475° C. and a pressure in the roll gap of approximately 6000t. This was followed, if necessary, by a cold rolling process to achieve plate thicknesses below 9 mm. By means of the rolling process a second metallurgical bond between powder and cover layer was achieved and the powder was further compacted to approximately 98% to 100% of its nominal density. The resulting triple-layer sheets were then finished and fed to the foaming method.

(8) The above method was also carried out with the following aluminum alloys for the metal in the powder mixture and the container as well as the following foaming agents in the quantities indicated:

(9) TABLE-US-00002 Alloy of the metal Alloy of the metal Example of the powder mixture Foaming agent.sup.1 of the container 2.1 AlSi8Mg4 TiH.sub.2 (1.0 wt. %) Al 6082 2.2 AlSi8Mg4 TiH.sub.2 (0.5 wt. %) Al 5754 2.3 AlSi8Mg4 TiH.sub.2 (0.6 wt. %) Al 5005 2.4 AlSi8Mg4 TiH.sub.2 (0.6 wt. %) Al 6016 2.5 AlSi7 TiH.sub.2 (1.2 wt. %) Al 3103 2.6 AlSi6Cu7.5 TiH.sub.2 (0.8 wt. %) Al 6060 .sup.1The specification of the quantity of foaming agent in weight % (wt. %) is based on the total quantity of the powder mixture. The same method was also carried out with the following foaming agents instead of TiH.sub.2: 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 combinations of TiH.sub.2 with LiBH.sub.4 and TiH.sub.2 with LiAlH.sub.4.