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(11) | EP 2 567 764 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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| (54) |
Master alloy production for glassy aluminum-based alloys Herstellung einer Masterlegierung für glasige Legierungen auf Aluminiumbasis Production d'alliage maître pour alliages d'aluminium vitreux |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
BACKGROUND
[0001] Aluminum alloys are important in many industries. Glassy Al-based alloys and their devitrified derivatives are currently being considered for applications in the aerospace industry. These alloys involve the addition of rare earth and transition metal elements. These alloys have high strength and, when processed appropriately, have high ductility.
[0002] One of the key requirements for high ductility is control of the uptake of hydrogen. While all Al-based alloys are sensitive to hydrogen, alloys containing rare earth elements are particularly susceptible to the effects of hydrogen during alloy production.
[0003] When Al-based alloys are produced in large quantities, they are often direct chill cast into molds that drop into well-like openings in the ground. For reactive materials such as Al-Li-X alloys, care must be exercised to preclude or prevent reaction of the Li with any oxidant such as air or water. For more reactive elements such as Yttrium and other rare earths, even more care is needed because exposure to water that is used to cool direct chill molds could result in fire and/or an explosion.
[0004] Al-based alloys such as Al-Y-Ni-Co alloys are devitrified glass-forming aluminum alloys that derive their strength from a nanometer-sized grain structure and nanometer-sized intermetallic phase or phases. The presence of hydrogen destroys the ductility of these alloys. Consequently, it is necessary to produce master alloys with hydrogen contents of 1 ppm or less. Examples of such alloys are disclosed in co-owned U.S. Patents No, 6,974,510 and 7,413,621.
[0005] It is necessary to find an alternative process for production of these highly reactive Al-based alloys.
SUMMARY
[0006] It has now been discovered that master alloy for devitrified glass-forming Al-based alloys can be produced in a process that avoids hydrogen pickup. The molten metal is isolated from the environment to a substantial degree. The process includes the use of a bottom-pour or side-pour crucible that is "covered" with an inert gas such as argon. The gas cover includes a physical cover on the top of the crucible into which argon or another inert gas such as nitrogen is bled into the crucible to form a positive pressure. The heavier argon forces out any air to minimize exposure of the melt to air.
[0007] The metal is poured out from the side or bottom of the crucible, rather than tipping to pour out the top. It is poured into a launder or pipe that is sealed and attached to the crucible, and is also filled with an inert gas such as argon. The molten metal flows through a launder or launder/tundish combination and is deposited directly into molds, which are also filled with inert gas such as argon.
[0008] The present invention provides apparatus for forming aluminum alloy ingots, comprising: a sealed chamber having a source of inert gas; a crucible positioned inside the chamber for melting aluminum alloy input stock including, but not limited to, chips, shot, rod, bar, etc., the sealed chamber having a solid top and a source of inert gas therein adapted to drive out other atmosphere; an outlet in the crucible positioned to draw molten alloy from the crucible at a point proximate the lowest point in the crucible; and a tundish adapted to control the flow of molten alloy from the crucible on a path to at least one ingot mold while maintaining an inert atmosphere during the flow of alloy to the mold and out of the sealed chamber.
[0009] In another aspect the present invention provides a method of forming aluminum alloy ingots, comprising the steps of: melting aluminum alloy feed stock in a crucible having an inert atmosphere; drawing molten alloy from the crucible at a point below the inert atmosphere; and maintaining an inert atmosphere during the flow of alloy from the crucible to a mold.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Certain preferred embodiments will now be described by way of example only and with reference to the accompanying drawings.
FIG. 1 shows one embodiment of a bottom pour furnace with a vertical feed for producing aluminum alloy ingots while avoiding hydrogen pickup.
FIG. 2 shows another embodiment of a bottom pour furnace with a horizontal feed for producing aluminum alloy ingots while avoiding hydrogen pickup.
FIG. 3 is a possible cross section for the horizontal feed launders of the apparatus of FIG. 2.
FIG. 4 is a flow diagram illustrating the method of forming aluminum master alloy ingots.
DETAILED DESCRIPTION
[0011] FIG. 1 illustrates a bottom pour furnace 10 generally with a vertical feed. The entire furnace is inside an inert chamber 11, having a solid top 17, with gas feed 13 introducing argon or another inert gas such as nitrogen. It is more effective if the inert gas is heavier than air, as argon is, to more easily push out any air that is initially present in chamber 11. A top-feed crucible 15 is located inside chamber 11. Inside crucible 15 is a quantity of aluminum and various alloy elements in the form of chips, shot, rod, etc. that is to be made into master alloy ingots. The aluminum alloy can be any alloy but it has been discovered that the glassy devitrified alloys such as those disclosed in co-owned U.S. Patents No, 6,974,510 and 7,413,621, can be formed into low oxygen and low hydrogen master alloy ingots using the method of this invention.
[0012] The alloy in crucible 15 is purged with argon or another inert gas to drive out oxygen and any other reactive gas. Hydrogen from moisture is also driven out. Crucible 15 may be any low moisture/low volatiles alumina crucible, such as those produced by St. Gobain, or a graphite crucible with a spall-free alumina coating. Typical crucibles are ceramic cylinders that are about two feet in diameter and about three feet deep.
[0013] The alloy is melted in crucible 15 and exits the bottom of crucible through launder 19, so that the flow of molten alloy is controlled by position-control door 21. Launder may not be needed in some designs of crucible 15. With or without launder 19, the passage out of crucible 15 is also accomplished in an inert atmosphere via inert gas feed 23.
[0014] Tundish 25 is a funnel-shaped vessel into which the molten metal is poured. The purpose of a tundish is to allow the molten metal to reach a desired height (with a desired head pressure) so that there is a constant pour rate. It has been discovered that a slower rate precluded bubbles from forming in the melt. The height can be adjusted so there is no splashing of the metal into the molds. Flowing molten alloy 27 pours into waffle ingot molds 29 carried by conveyor belt 31, also in an inert atmosphere.
[0015] Allowing the molten alloy to drain down from the bottom of crucible 15 eliminates a major problem in prior art furnaces, in that the dross that accumulates on the top of the molten pool of alloy remains at the top and does not have to be removed until crucible 15 is cleaned prior to recharging with more alloy. Also, the dew point can be monitored, further preventing undesirable gas from contacting the sensitive elements of the alloy, thus preserving the low hydrogen/oxygen content of the master alloy.
[0016] For the two embodiments as discussed herein, a hygrometer with a computer can be used for measuring the amount of moisture, and therefore hydrogen, in the gases both at the source for 13 and 23, and within chamber 11 as a function of time. Best results are obtained when the dew point is -110 °F (-78.9 °C) or lower. A commercially available monitor such as an ALSCAN may be connected to a computer so that hydrogen readings in the melt may also be taken in real time. Similar readings in the launder can be used to monitor hydrogen there as well, which is to be as low as possible, i.e., less than 1 ppm.
[0017] In an alternative embodiment, a bottom pour furnace 100 generally is shown in FIG. 2. A first inert chamber 111, having a solid top 117, is maintained in an inert state via inert gas feed 113. Crucible 115 is filled or purged with an inert gas to drive out all reactive gasses, including hydrogen via the gas from 113. A launder 119, angled downward, is maintained with an inert atmosphere by a plurality of inert gas feeds 123 downstream of metal flow control door 121. Launder 119 has a typical cross section as shown in FIG. 3, with a steel or other hard casing 141, a ceramic mold or center passage 143 and the opening 145 through which the molten alloy flows. Tundish 125 controls the pour rate and pour height of molten alloy into waffle ingot molds 129 that are carried by conveyor belt 131. Again inert gas is maintained in second inert chamber 211 by inert gas feed 213.
[0018] FIG. 4 is a flow diagram of the method of this invention. Aluminum and the required elements in the form of chips, shot, rod, etc. (Step 311) are selected and placed in an enclosed crucible having an inert atmosphere (Step 313) with a positive pressure to drive out other gasses. The input stock is melted (Step 315) to form a molten alloy. The molten alloy is transferred (Step 317) to a mold while maintaining an inert atmosphere at least until the ingot is solidified. The ingot is then removed (Step 319) and available for subsequent processing.
[0019] Both bottom and side pouring embodiments have been found to be effective in producing satisfactory ingots. The advantage of the system of FIG. 1 is that the system is more compact with the launder going straight down. However, if the pouring goes too fast and can't be stopped, the risk of overpouring onto the floor exists. In the system of FIG. 2, more space is used but there can be multiple metal flow gates to contain failure at the bottom of the furnace.
[0020] While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention which is defined by the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
a sealed chamber (11; 111) having a source (13; 113) of inert gas;
a crucible (15; 115) positioned inside the chamber for melting aluminum alloy input stock, the sealed chamber having a solid top (17; 117) and a source of inert gas therein adapted to drive out other atmosphere;
an outlet in the crucible positioned to draw molten alloy from the crucible at a point proximate the lowest point in the crucible; and
a tundish (25; 125) adapted to control the flow of molten alloy from the crucible on a path to at least one ingot mold (29; 129) while maintaining an inert atmosphere during the flow of alloy to the mold and out of the sealed chamber.
melting aluminum alloy feed stock in a crucible (15; 115) having an inert atmosphere;
drawing molten alloy from the crucible at a point below the inert atmosphere; and
maintaining an inert atmosphere during the flow of alloy from the crucible to a mold (29; 129).
wherein the molten alloy is removed from the crucible through an outlet at a point proximate the lowest point of the crucible;
the method comprising the steps of:
controlling the flow of molten alloy from the crucible to the mold (29; 129), the flow being controlled with a tundish (25; 125); and removing the mold from the inert atmosphere.
eine dicht verschlossene Kammer (11; 111) mit einer Inertgas-Quelle (13; 113);
einen Tiegel (15; 115), der im Inneren der Kammer zum Schmelzen von Aluminiumlegierungs-Vormaterial angeordnet ist, wobei die dicht verschlossene Kammer eine massive Oberseite (17; 117) sowie eine in der Kammer vorgesehene Inertgas-Quelle aufweist, die zum Austreiben anderer Atmosphäre ausgebildet ist;
einen Auslass in dem Tiegel, der zum Abziehen von geschmolzener Legierung aus dem Tiegel an einer Stelle in der Nähe des tiefsten Punkts in dem Tiegel positioniert ist; und
einen Verteiler (25; 125), der zum Steuern des Flusses von geschmolzener Legierung aus dem Tiegel auf einem Weg zu mindestens einer Gießform (29; 129) ausgebildet ist, während eine inerte Atmosphäre während des Flusses von Legierung in die Form sowie aus der dicht verschlossenen Kammer hinaus aufrecht erhalten bleibt.
wobei der Auslass an dem Tiegel (15) derart positioniert ist, dass Legierung aus dem Boden des Tiegels ausströmen kann.
wobei der Auslass an dem Tiegel (115) derart positioniert ist, dass Legierung von der unteren Seite des Tiegels ausströmen kann.
wobei der Auslass eine Rinne (19; 119) mit zylindrischem Querschnitt zum Übertragen der geschmolzenen Legierung von dem Tiegel (15; 115) zu dem Verteiler (25; 125) aufweist.
wobei das Inertgas Argon ist.
wobei die Legierung eine entglaste glasbildende Aluminiumlegierung mit einer nanometergroßen Kornstruktur und einer nanometergroßen intermetallischen Phase oder Phasen ist.
Schmelzen von Aluminiumlegierungs-Zufuhrmaterial in einem Tiegel (15; 115) mit einer inerten Atmosphäre;
Abziehen von geschmolzener Legierung aus dem Tiegel an einer Stelle unterhalb der inerten Atmosphäre; und
Aufrechterhalten einer inerten Atmosphäre während des Flusses von Legierung aus dem Tiegel in eine Form (29; 129).
wobei der Auslass des Tiegels (15) nahe dem Boden des Tiegels angeordnet ist.
wobei der Auslass des Tiegels (115) derart angeordnet ist, dass Legierung von der unteren Seite des Tiegels ausströmen kann.
wobei das Übertragen der geschmolzenen Legierung von dem Tiegel (15; 115) zu der Form (29; 129) mittels einer Rinne mit einem zylindrischen oder anderem Querschnitt ausgeführt wird.
wobei das Inertgas Argon ist.
wobei die Legierung eine entglaste glasbildende Aluminiumlegierung mit einer nanometergroßen Kornstruktur und einer nanometergroßen intermetallische Phase oder Phasen ist.
wobei der Tiegel (15; 115) in einer Kammer (11; 111) angeordnet ist, die eine inerte Atmosphäre mit einem ausreichenden Druck zum Austreiben von Umgebungsatmosphäre aufweist, wobei der Tiegel das Zufuhrmaterial zu einer geschmolzenen Legierung schmilzt;
wobei die geschmolzene Legierung aus dem Tiegel durch einen Auslass an einer Stelle nahe dem tiefsten Punkt des Tiegels abgeführt wird; wobei das Verfahren folgende Schritte aufweist:
Steuern des Flusses der geschmolzenen Legierung von dem Tiegel in die Form (29; 129), wobei der Fluss mittels eines Verteilers (25; 125) gesteuert wird; und Entfernen der Form aus der inerten Atmosphäre.
das ferner den Schritt des Haltens des Taupunkts in dem Tiegel (15; 115) zwischen -35 °F (-37,2 °C) und -110 °F (-78,9 °C) oder darunter beinhaltet.
une chambre hermétique (11 ; 111) ayant une source (13 ; 113) de gaz inerte ;
un creuset (15 ; 115) positionné à l'intérieur de la chambre pour fondre la matière de base en alliage d'aluminium, la chambre hermétique ayant un dessus plein (17 ; 117) et une source de gaz inerte à l'intérieur adaptée pour chasser une autre atmosphère ;
un refoulement dans le creuset positionné pour démouler l'alliage fondu du creuset en un point à proximité du point le plus bas dans le creuset ; et
un panier de coulée (25 ; 125) adapté pour réguler l'écoulement d'alliage fondu du creuset sur un chemin à au moins une lingotière (29 ; 129) tout en maintenant une atmosphère inerte pendant l'écoulement d'alliage jusqu'à la lingotière et hors de la chambre hermétique.
fondre une matière première en alliage d'aluminium dans un creuset (15 ; 115) ayant une atmosphère inerte ;
démouler l'alliage fondu du creuset en un point en dessous de l'atmosphère inerte ; et
maintenir une atmosphère inerte pendant l'écoulement de l'alliage du creuset à une lingotière (29 ; 129).
dans lequel l'alliage fondu est retiré du creuset à travers un refoulement en un point à proximité du point le plus bas du creuset ;
le procédé comprenant les étapes consistant à :
réguler l'écoulement d'alliage fondu du creuset à la lingotière (29 ; 129), l'écoulement étant régulé avec un panier de coulée (25 ; 125) ; et retirer la lingotière de l'atmosphère inerte.
REFERENCES CITED IN THE DESCRIPTION
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.
Patent documents cited in the description