BRPI0419350B1 - METHOD AND INDUCTION FOR PRODUCTION OF COMPOUND METAL INGLES AND COMPOUND METAL INGOTS - Google Patents

Description

Report of the Invention Patent for "METHOD AND APPARATUS FOR PRODUCTION OF COMPOUND METAL LANGUAGES AND COMPOUND METAL LANGUAGE".

Divided from PI 0411851-0, filed June 23, 2004 Background of the Invention The present invention relates to a method and equipment for ingot composite metal ingots as well as novel composite metal ingots obtained therefrom.

Background Art For many years metal ingots, particularly aluminum or aluminum alloy ingots, have been produced by a semi-continuous casting process known as direct cooling casting. In this procedure the molten metal is poured onto the top of an open-ended mold and a cooling medium, typically water, is applied directly to the metal solidifying surface as it emerges from the mold.

[004] Such a system is commonly used to produce large rectangular section ingots for the production of rolled products, for example aluminum alloy sheet products. There is a large market for composite ingots consisting of two or more layers of different alloys. Such ingots are used to produce, after rolling, coated sheets for various applications such as welding sheets, aircraft sheets and other applications where surface properties are desired to differ from those of the core.

The conventional approach to such a coated sheet has been to heat plates of different alloys together to "fix" the two joints, then to continue rolling until the finished product is produced. This has the disadvantage that the interface between the plates is generally not metallurgically clean and layer bonding can be a problem.

There has also been an interest in casting ingot layers to produce a composite ingot ready for rolling. This has typically been accomplished using either direct cooling (DC) casting, or by the simultaneous solidification of two alloy streams or by sequential solidification where one metal is solidified before being contacted by a second molten metal. In the literature a number of such methods have been described which have obtained varying degrees of success.

[007] In Binczewski, US Patent 4,567,936, issued February 4, 1986, a method for producing a direct-cooling ingot where a higher outer solids temperature layer is melted over an inner layer with a lower solids temperature. The description states that the outermost layer must be "completely solid and whole" at the moment when the lowest solids alloy contacts it.

[008] Keller, German Patent 844 806, published July 24, 1952, describes a single mold for casting a layered structure where the inner core is cast before the outer layer. In this procedure, the outer layer is fully solidified before the inner alloy contacts it.

In Robinson, U.S. Patent 3,353,934, issued November 21, 1967, a casting system is described wherein an internal division is placed within the mold cavity to substantially separate areas of different alloy compositions. The end of the deflector is designed so that it ends in the "pasty zone" just above the solidified portion of the ingot. Within the "pasty zone" the alloy is free to mix under the deflector end to form a joint between the layers. However, the method is not controllable in the sense that the deflector used is "passive" and casting depends on controlling the location of the container, which is indirectly controlled by the cooling system.

In Matzner, German Patent DE 44 20 697, published December 21, 1995, a casting system using a Robinson-like internal division is described, in which the position of the deflector container is controlled to allow mixing of the liquid phase of the interface zone create a continuous concentration gradient across the interface.

In Robertson et al., British Patent GB 1,174,764, issued December 21, 1965, a movable deflector is provided for splitting a common casting caster and allowing casting of two different metals. The deflector is movable to allow in one limit the materials to mix and in another limit to cast two separate shafts.

In Kilmer et al., WO Publication 2003/035305, published May 1, 2003, a casting system is described using a barrier material in the form of a thin sheet between two layers of different alloys. The thin sheet has a sufficiently high melting point that it remains intact during casting and is incorporated into the final product.

Takeuchi et al., US Patent 4,828,015, issued May 9, 1989, describes a method of casting two liquid alloys into a single mold by creating a division in the liquid zone by means of a magnetic field and feed. of the two zones with separate alloys. The alloy which is fed to the upper portion of the zone thus forms a shell around the metal fed to the lower portion.

Veillette, US Patent 3,911,996, describes a mold having a flexible outer wall to adjust the shape of the ingot during casting, Steen et al., US Patent 5,947,194, describes a mold similar to Veillette but allowing greater shape control, Takeda et al., US Patent 4,498,521 describes a metal level control system using a float on the metal surface to measure metal level and report to flow control.

Odegard et al., U.S. Patent 5,526,870, describes a metal level control system using a remote sensing probe (radar).

Wagstaff, U.S. Patent 6,260,602 describes a mold having a variably narrow wall for controlling the external shape of an ingot.

It is an object of the present invention to produce a composite metal ingot consisting of two or more layers having an improved metallurgical bond between adjacent layers. It is also an object of the present invention to provide a means for controlling the temperature of the interface where two or more layers joining together in a composite ingot to improve metallurgical bonding between adjacent layers.

It is also an object of the present invention to provide a means for controlling the shape of the interface where two or more alloys are combined into one composite metal ingot.

It is another object of the present invention to provide a sensitive method for controlling the metal level in an ingot mold that is particularly useful in confined spaces.

Description of the Invention An embodiment of the present invention is a method for casting a composite metal ingot comprising at least two layers formed of one or more alloy compositions. The method comprises providing an open-ended annular mold having a feed end and an outlet end where molten metal is added at the feed end and solidified ingot is extracted at the outlet end. Partition walls are used to divide the feed end into at least two separate feed chambers, the partition walls ending above the mold exit end, and where each feed chamber is adjacent to at least one other feed chamber. For each pair of adjacent feed chambers a first stream of a first alloy is fed to a chamber of the feed chamber pair to form a metal pool in the first chamber and a second stream of a second alloy is fed through the second chamber of the feed chamber. pair of feed chambers to form a metal pool in the second chamber. The first metal puddle contacts the dividing wall between the pair of chambers to cool the first puddle to form a self-supporting surface adjacent to the dividing wall. The second metal pool is then brought into contact with the first pool so that the second pool initially contacts the self-supporting surface of the first pool at a point where the temperature of the self-supporting surface is between the solidus and liquidus temperatures of the first. turns on. The two pools of alloys are therefore joined as two layers and cooled to form a composite ingot.

Preferably the second alloy initially contacts the self-supporting surface of the first alloy when the temperature of the second alloy is above the liquidus temperature of the second alloy. The first and second alloys may have the same alloy composition or may have different alloy compositions.

Preferably the upper surface of the second alloy contacts the self-supporting surface of the first puddle at a point where the temperature of the self-supporting surface is between the solidus and liquidus temperatures of the first alloy.

In this embodiment of the invention the self-supporting surface may be generated by cooling the first alloy puddle so that the surface temperature at the point where the second alloy initially contacts the self-supporting surface is between solidus and liquidus temperatures. .

Another embodiment of the present invention comprises a method for casting a composite metal ingot comprising at least two layers formed of one or more alloy compositions. Such a method comprises providing an open-ended annular mold having a feed end and an outlet end where molten metal is added to the feed end and the solidified ingot is extracted at the outlet end. Partition walls are used to divide the feed end into at least two separate feed chambers, the partition walls ending above the mold exit end, and where each feed chamber is adjacent to at least one other feed chamber. For each pair of adjacent feed chambers, a first stream of a first alloy is fed to a chamber of the feed chamber pair to form a metal pool in the first chamber and a second stream of a second alloy is fed through the second chamber. the pair of feed chambers to form a metal pool in the second chamber. The first metal puddle contacts the dividing wall between the pair of chambers to cool the first puddle to form a self-supporting surface adjacent to the dividing wall.

The second metal pool is then brought into contact with the first pool so that the second pool contacts the self-supporting surface of the first pool at a point where the temperature of the self-supporting surface is below the solidus temperature of the first pool. alloy to form an interface between the two alloys. The interface is then reheated to a temperature between solidus and liquidus temperatures of the first alloy such that the two alloy pools are therefore joined as two layers and cooled to form a composite ingot.

In this embodiment, reheating is preferably achieved by allowing the latent heat within the first or second puddles to reheat the surface.

Preferably the second alloy initially contacts the self-supporting surface of the first alloy when the temperature of the second alloy is above the liquidus temperature of the second alloy. The first and second alloys may have the same alloy composition or may have different alloy compositions.

Preferably the upper surface of the second alloy contacts the self-supporting surface of the first puddle at a point where the temperature of the self-supporting surface is between the solidus and liquidus temperatures of the first alloy.

The self-supporting surface may also have an oxidized layer formed therein. It is strong enough to withstand the increased forces normally causing the metal to spread when not confined. These increased forces include the forces created by the metallostatic pressure of the first stream, and surface expansion in the case where cooling extends below the solid followed by surface reheating. By bringing the second liquid alloy into contact with the first alloy while the first alloy is still in the semi-solid state or, and in the alternative mode, ensuring that the interface between the alloys is reheated to a semi-solid state, a layer of Distinct but binder interface is formed between the two alloys. In addition, the fact that the interface between the second alloy layer and the first alloy is therefore formed before the first alloy layer has developed a rigid shell means that the stress created by the direct application of the cooling medium to the outer surface of the alloy. Ingot is better controlled in the finished product, which is particularly advantageous when casting alloys that tend to fracture.

The result of the present invention is that the interface between the first and second alloys is maintained over a short length of the emerging ingot at a temperature between the solidus and liquidus temperatures of the first alloy. In a particular embodiment, the second alloy is fed into the mold such that the upper surface of the second alloy in the mold is in contact with the surface of the first alloy where the surface temperature is between solidus and liquidus temperatures and thus an interface is formed. having achieved this requirement. In an alternative embodiment, the interface is reheated to a temperature between solidus and liquidus temperatures just after the upper surface of the second alloy contacts the self-supporting surface of the first alloy. Preferably the second alloy is above its liquidus temperature when it initially contacts the surface of the first alloy. When this is done, the integrity of the interface is maintained but at the same time certain alloying components are sufficiently mobile throughout the interface so that metallurgical agglutination is facilitated.

If the second alloy is contacted where the surface temperature of the first alloy is sufficiently below the solidus temperature (e.g., after a significant solidus shell has been formed), and there is insufficient latent heat to reheat the interface to temperature. between solidus and liquidus temperatures of the first alloy, then the mobility of the alloying components is very limited and insufficient metallurgical agglutination is formed. This may cause layer separation during subsequent processing.

If the self-supporting surface is not formed in the first alloy before the second alloy contacts the first alloy, then the alloys are free to mix and a diffuse layer or alloy concentration gradient is formed at the interface, rendering the least distinctive interface.

It is particularly preferred that the upper surface of the second alloy is maintained a position below the lower edge of the partition wall. If the upper surface of the second alloy in the mold is above the point of contact with the surface of the first alloy, for example above the lower edge of the partition wall, then there is a danger that the second alloy may rupture the self-supporting surface of first alloy or even completely relingote the surface because of excess latent heat. If this happens, there may be an excessive mix of alloys at the interface, or in some cases metal leakage or casting failure. If the second alloy contacts the partition wall particularly far from the lower edge, it may even be prematurely cooled to a point where contact with the self-supporting surface of the first alloy no longer forms strong metallurgical agglutination. In certain cases, however, it may be advantageous to keep the upper surface of the second alloy near the lower edge so that the partition wall can act as an oxide skimmer to prevent surface oxides of the second layer from being incorporated into the interface between the two. two layers. This is particularly advantageous where the second layer is oxidizable. In any case the position of the upper surface must be carefully controlled to avoid the problems noted above, and should not be more than 3 mm above the lower edge of the partition.

In all the foregoing embodiments it is particularly advantageous to contact the second alloy with the first alloy at a temperature between the solidus temperature and the coherence temperature of the first alloy or to reheat the interface between the two to a temperature between the solidus temperature. and the coherence temperature of the first alloy. The point of coherence, and the temperature (between solidus and liquidus temperatures) at which this occurs is an intermediate step in solidification of the molten metal. As dendrites grow in size in a cooled molten metal and begin to collide with each other, a continuous solid network develops through the volume of the alloy. The point at which there is a sudden increase in the torque force required to cut the solid grid is known as the "point of coherence". The description of the coherence point and its determination can be found in Solidification Characteristics of Aluminum Alloys, Volume 3, Dendrite Coherency Pg. 210

In another embodiment of the invention, there is provided a metal casting equipment comprising an open end annular mold having a feed end and an outlet end and a lower block that fits within the outlet end and is movable on a direction along the axis of the annular mold. The feed end of the mold is divided into at least two separate feed chambers, where each feed chamber is adjacent to at least one other feed chamber and where the feed chambers adjacent to it are separated by a temperature controlled dividing wall which can add or remove heat. The dividing wall terminates above the exit end of the mold. Each chamber includes a metal level control device such that in adjacent pairs of chambers the metal level in one chamber may be held at a position above the lower end of the dividing wall between chambers and in the other chamber may be held at a different position. level in the first chamber.

Preferably the level in the other chamber is kept at a position below the lower end of the partition wall.

The partition wall is designed so that the extracted or added heat is calibrated to create a self-supporting metal surface in the first chamber adjacent to the partition wall to control the temperature of the self-supporting metal surface in the first chamber. to stay between solidus and liquidus temperatures and a point where the upper surface of the metal in the second chamber can be maintained.

The temperature of the self-supporting layer can be carefully controlled by removing heat from the partition wall through a temperature control fluid being passed through a part of the partition wall or brought into contact with the partition wall at its end. to control the temperature of the self-supporting layer.

Another embodiment of the invention is a method of casting a composite metal ingot comprising at least two different alloys comprising providing an open-ended annular mold having a feed end and an outlet end and dividing means. the feed end is in at least two separate feed chambers, where each chamber is adjacent to at least one other feed chamber. For each pair of adjacent feed chambers, a first stream of a first alloy is fed through one of the feed chambers adjacent to said mold, a second stream of a second alloy is fed through another of the adjacent feed chambers. A temperature-controlling partition wall is provided before the adjacent feed chambers such that the point at the interface where the first and second alloys initially contact each other is maintained at a temperature between the solidus and liquidus temperatures of the first alloy by means of a control-partition wall. where the currents are joined as two layers. The layers of bonded alloys are cooled to form a composite ingot.

The second alloy is preferably brought into contact with the first alloy just below the lower end of the partition wall without first contacting the partition wall. In any case, the second alloy should contact the first alloy not less than 2 mm below the lower end of the partition wall but not more than 20 mm and preferably about 4 to 6 mm below the lower end of the partition wall.

If the second alloy contacts the partition wall before contacting the first alloy, it may be prematurely cooled to a point where contact with the self-supporting surface of the first alloy no longer forms strong metallurgical agglutination. Even if the liquidus temperature of the second alloy is sufficiently low this does not happen, the existing metallostatic pressure can cause the second alloy to be fed into the space between the first alloy and the partition wall and cause defects or casting failures. When the upper surface of the second alloy is desired to be above the lower end of the partition wall (for example, to remove oxides) it should be carefully positioned as nearly as possible to the lower end of the partition wall to avoid such problems.

The dividing wall between adjacent pairs of feed chambers may be tapered and the funnel may vary along the length of the dividing wall. The partition wall may also have a curvilinear shape. These features can be used to compensate for different thermal and solidification properties of the alloys used in the chambers separated by the partition wall and thus provide control of the geometry of the emerging interface within the emerging ingot. The curvilinear wall can also serve to form layered ingots having specific geometries that can be rolled with less loss. The dividing wall between adjacent pairs of feed chambers can also be made flexible and can be adjusted to ensure that the interface between the two alloy layers in the final ingot and the rolled product is straight regardless of the alloys used and is straight even in the section. match.

Another embodiment of the invention is a composite metal ingot casting equipment, comprising an open-ended annular die having a feed end and an outlet end and a lower block that fits within the outlet end and protrudes into the casting. moves along the mold axis. The feed end of the mold is divided into at least two separate feed chambers, where each feed chamber is adjacent to at least one other feed chamber and where the adjacent feed chambers are separated by a partition wall. The partition wall is flexible, and a positioning device is attached to the partition wall so that the curvature of the wall in the mold plane can be varied by a certain amount during operation.

Another embodiment of the invention is a method for casting a composite metal ingot comprising at least two different alloys comprising providing an open end ring die having a feed end and an outlet end and means for dividing the feed end into at least two separate feed chambers, where each feed chamber is adjacent to at least one other feed chamber. For adjacent pairs of feed chambers, a first stream of a first alloy is fed through one of the adjacent feed chambers into the mold, and a second stream of a second second alloy stream is fed through another of the adjacent feed chambers. .

A flexible partition wall is provided between adjacent chambers and the curvature of the flexible partition wall is adjusted during casting to control the shape of the interface where the alloys are joined as two layers. The bonded alloy layers are then cooled to form a composite ingot having a fully uniform interface.

Metal feeding requires careful level control and one method for this is to provide a slow flow of gas, preferably an inert gas, through a pipe with an opening at a fixed point relative to the annular mold body. The opening is immersed in use below the metal surface in the mold, the gas pressure is measured and the metallostatic pressure above the pipe opening is therefore determined. The measured pressure can then be used to directly control the metal flow in the mold to keep the upper surface of the metal at a constant level.

Another embodiment of the invention is a method of casting a metal ingot comprising providing an open-ended annular mold having a feed end and an outlet end, and feeding a molten metal into the feed end. of said mold to create a metal puddle within said mold having a surface. The end of the gas delivery tube is immersed in the metal pool from the mold tube feed end at a predetermined position relative to the mold body and an inert gas is bubbled through the gas delivery tube to a slow enough to keep the tube thawed. The gas pressure within said pipe is measured to determine the position of the molten metal relative to the mold body.

Another embodiment of the invention is an ingot casting equipment comprising an open-ended annular die having a feed end and an outlet end having a lower block that fits at the exit end and is movable. along the axis of the mold. A metal flow control device is provided for controlling the rate at which metal can flow into the mold from an external source, and a metal level sensor comprising a gas delivery tube attached to a gas source is also provided. gas through a gas flow controller and having an open end positioned at a predefined location below the feed end of the mold such that, in use, the open end of the pipe is normally below the metal level in the mold. mold. A means for measuring the gas pressure in the gas delivery tube between the flow controller and the open end of the gas delivery tube is also provided, the measured gas pressure being adapted to control the gas flow control device. to maintain the metal, on which the open end of the gas delivery tube is placed, at a predetermined level.

[0052] This metal level measuring method and apparatus is particularly useful for measuring and controlling metal level in a confined space such as in some or all of the feed chambers in a multi-chamber mold design. They can be used in conjunction with other metal level control systems that use floats or other similar surface positioning monitors, where, for example, a gas tube is used in smaller feed chambers and a feed control system. based on a float or similar device in the larger feed chambers.

In a preferred embodiment of the present invention there is provided a method for casting a composite ingot having two different alloy layers, where an alloy forms a layer on the widest surface or "rolling" face of a rectangular cross-section ingot. formed from another alloy. For this procedure an open-ended annular mold having a feed end and an outlet end and means for dividing the feed end into adjacent feed chambers separated by a temperature-controlled dividing wall is provided. The first stream of a first alloy is fed through one of the feed chambers in the mold and a second stream of a second alloy is fed through another of the feed chambers, this second alloy having a lower liquidus temperature than the first alloy. . The first alloy is cooled by the temperature controlled partition wall to form a self-supporting surface extending below the lower end of the partition wall, and the second alloy is contacted with the self-supporting surface of the first alloy at a location where the temperature of Self-sustaining surface is maintained between the solidus and liquidus temperatures of the first alloy, whereby the two alloy streams are joined as two layers. The bonded alloy layers are then cooled to form a composite ingot.

In another preferred embodiment the two chambers are configured such that an outer chamber completely surrounds the inner chamber whereby an ingot having an alloy layer completely enclosing the core of a second alloy is formed.

A preferred embodiment includes two laterally spaced temperature-controlled partition walls forming three feed chambers. Thus, there is a central feed chamber with a dividing wall on each side and a pair of external feed chambers on either side of the central feed chamber. A first alloy stream may be fed through the central feed chamber, with second alloy chains being fed into the two side chambers. Such an arrangement is typically used to provide two layers of coating on a central core material.

It is also possible to reverse the procedure so that streams from the first alloy are fed through the side chambers while a stream from the second alloy is fed through the central chamber. With this arrangement, the casting is initiated in the side feed chambers with the second alloy being fed through the central chamber and contacting the pair of first alloys just below the partition walls.

The ingot cross-sectional shape can be any convenient shape (e.g. circular, square, rectangular or any other regular or irregular shape) and the cross-sectional shapes of the individual layers may also vary within the ingot.

Another embodiment of the invention is a cast ingot product consisting of an elongated ingot comprising, in cross section, two or more separate alloy layers of different compositions, where the interface between adjacent alloy layers is in the form of an agglutination. substantially continuous metallurgical This agglutination is characterized by the presence of dispersed particles of one or more first alloy intermetallic compositions in a region of the second alloy adjacent to the interface. Generally, in the present invention the first alloy is one in which a self-supporting surface is initially formed and the second alloy is brought into contact with this surface while the surface temperature is between the solidus and liquidus temperatures of the first alloy, or the interface. It is subsequently heated to a temperature between the solidus and liquidus temperatures of the first alloy. The dispersed particles are preferably less than about 20 µm in diameter and are discovered in a region of up to about 200 µm of the interface.

Agglutination may also be characterized by the presence of ridges or secretions of one or more intermetallic compositions of the first alloy extending from the interface to the second alloy in the region adjacent to the interface. This feature is particularly formed when the self-supporting surface temperature has not been reduced to below the solidus temperature prior to contact with the second alloy.

The ridges or secretions preferably penetrate less than about 100 pm into the second alloy from the interface.

Where intermetallic compositions of the first alloy are dispersed or exuded in the second alloy, a layer which contains a reduced amount of intermetallic particles and which may consequently form a layer remains in the first alloy, adjacent to the interface between the first and second alloys. which is nobler than the first alloy and can impart corrosion resistance to the coating material. This layer is typically 4 to 8 pm thick.

This agglutination may also be characterized by the presence of a diffuse layer of first alloy alloy components in the second alloy layer adjacent to the interface. This feature is particularly formed in cases where the surface of the first alloy is cooled below the solidus temperature of the first alloy and then the interface between the first and second alloys is reheated to solidus and liquidus temperatures.

Although not wishing to be bound by any theory, it is believed that the presence of these characteristics is caused by the formation of segregated first alloy intermetallic compounds on the self-sustaining surface formed therein with their subsequent dispersion or exudation in the second alloy thereafter. contact the surface. The exudation of intermetallic compounds is aided by the displacement forces present at the interface.

Another feature of the interface between the layers formed by the methods of this invention is the presence of second alloy alloy components between the first alloy grain boundaries immediately adjacent to the interface between the two alloys. These are believed to arise when the second alloy (still generally above its liquidus temperature) contacts the self-supporting surface of the first alloy (at a temperature between the solidus and liquidus temperatures of the first alloy). Under these specific conditions, the alloy component of the second alloy may diffuse a short distance (typically about 50 pm) along the boundaries of still liquid grains, but not into grains already formed on the surface of the first alloy. If the interface temperature is above the liquidus temperature of both alloys, the general alloying will occur, and the components of the second alloy will be found within the grain as well as within the grain boundary. If the interface temperature is below the solidus temperature of the first alloy, there is no opportunity for grain boundary diffusion to occur.

The specific interfacial features described are specific features caused by solid state diffusion, or diffusion or movement of elements along restricted liquid paths, and do not affect the generally distinct nature of the total interface.

Regardless of how the interface is formed, the unique interface structure provides strong metallurgical bonding at the interface and thus makes the structure suitable for sheet lamination without problems associated with layer separation or interface contamination.

In yet another embodiment of the invention there is a composite metal ingot comprising at least two metal layers, where pairs of adjacent layers are formed by contacting the second metal layer with the surface of the first metal layer. such that when the second metal layer begins to contact the surface of the first metal layer, the surface of the first metal layer is at a temperature between its solidus and liquidus temperatures and the temperature of the second metal layer is above its temperature. liquidus temperature. Preferably the two metal layers are composed of different alloys.

Similarly in yet another embodiment of the invention, there is a composite metal ingot comprising at least two metal layers, where pairs of adjacent layers are formed by the contact of the second metal layer with the surface of the first metal layer of such that when the second metal layer initiates contact with the surface of the first metal layer, the surface of the first metal layer is below its solidus temperature and the temperature of the second metal layer is above its liquidus temperature. and the interface formed between the two metal layers is subsequently reheated to a temperature between the solidus and liquidus temperatures of the first alloy. Preferably the two metal layers are composed of different alloys.

In a preferred embodiment, the ingot has rectangular cross section and comprises a first alloy core and at least one second alloy surface layer, the surface layer being applied to the larger side of the rectangular cross section. This composite metal ingot is preferably hot and cold rolled to form a composite metal sheet.

In a particularly preferred embodiment, the core alloy is an aluminum-manganese alloy and the surface alloy is an aluminum-silicon alloy. Such compound ingot when hot and cold rolled forms a composite metal weld sheet which can be subjected to a welding operation to form a corrosion resistant welded structure.

In another particularly preferred embodiment, the core alloy is an aluminum scrap alloy and the surface alloy is a pure aluminum alloy. Such composite ingots when hot and cold rolled to form composite metal sheets provide economical recycled products having improved corrosion resistance, surface finish, etc. properties. In the present context, a pure aluminum alloy is an aluminum alloy having a thermal conductivity greater than 190 watts / m / K and a solidification range of less than 50 * 0.

In yet another particularly preferred embodiment the core alloy is a non-heat treated high strength alloy (such as an Al-Mg alloy) and the surface alloy is a weldable alloy (such as an Al-Si alloy) . Such compound ingots when hot and cold rolled to form composite metal sheets may undergo a forming operation and used for automotive structures which may then be welded or joined similarly.

In yet another particularly preferred embodiment the alloy core is a high strength heat treatable alloy (such as a 2xxx alloy) and the surface alloy is a pure aluminum alloy. Such compound ingots when hot and cold rolled form composite metal foils suitable for aircraft structures. Pure alloy may be selected for corrosion resistance or surface finish and should preferably have a solidus temperature greater than the solidus temperature of the core alloy.

In yet another preferred embodiment the core alloy is a medium strength heat treatable alloy (such as an Al-Mg-Si alloy) and the surface alloy is a pure aluminum alloy. Such compound ingots when hot and cold rolled form composite metal sheets suitable for automotive finishes. Pure alloy may be selected for corrosion resistance or surface finish and should preferably have a solidus temperature higher than the solidus temperature of the core alloy.

In another preferred embodiment, the ingot has a cylindrical cross-section and comprises a first alloy core and a concentric surface layer of the second alloy. In yet another preferred embodiment, the ingot has square or rectangular cross-section and comprises a second alloy core and an annular first alloy surface layer.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings illustrating certain preferred embodiments of this invention: Figure 1 is a partial section elevation view showing a single partition wall;

[0078] Figure 2 is a schematic illustration of contact between alloys;

[0079] Figure 3 is a partial section elevation view similar to Figure 1, but showing a pair of partition walls;

[0080] Figure 4 is a partial section elevation view similar to Figure 3, but with the second alloy having a liquidus temperature lower than that of the first alloy being fed into the central chamber;

Figures 5a, 5b and 5c are plan views showing some alternative arrangements of feed chambers that may be used with the present invention;

[0082] Figure 6 is an enlarged partial section view of a part of figure 1 showing a curvature control system;

Figure 7 is a plan view of a mold showing the effects of the variable curvature of the partition wall;

Figure 8 is an enlarged view of a part of Figure 1 illustrating a narrow dividing wall between the alloys;

Figure 9 is a plan view of a mold showing a particularly preferred embodiment of a partition wall;

Fig. 10 is a schematic view showing the metal level control system of the present invention;

Fig. 11 is a perspective view of a feed system for one of the feed chambers of the present invention;

Figure 12 is a plan view of a mold showing another preferred embodiment of the partition wall;

Figure 13 is a photomicrograph of a section through the union face between a pair of adjacent alloys using the method of the present invention showing the formation of intermetallic particles in the opposite alloy;

Figure 14 is a micrograph of a section through the same joint face as in Figure 13 showing the formation of intermetallic ridges or exudates;

Fig. 15 is a microphotograph of a section through the joint face between a pair of adjacent alloys processed under conditions outside the scope of the present invention;

Figure 16 is a micrograph of a section through the joint face between a coating alloy layer and a molten core alloy using the method of the present invention;

Figure 17 is a micrograph of a section through the joint face between a casing alloy and a molten core alloy using the method of the present invention, and illustrating the presence of the core alloy component alone along the grain boundary of the coating alloy on the joint face;

Figure 18 is a photomicrograph of a section through the joint face between a coating alloy layer and a molten core alloy using the method of the present invention, and illustrating the presence of diffused alloy components as in FIG. Figure 17; and Figure 19 is a microphotograph of a section through the joint face between a coating alloy layer and a molten core alloy using the method of the present invention, and also illustrating the presence of diffused alloy components. as in figure 17.

BEST MODES FOR CARRYING OUT THE INVENTION Referring to Figure 1, the caster ring assembly 10 has mold walls 11 forming part of a hydraulic jacket 12 from which a cooling water stream 13 is distributed.

The feeding portion of the mold is divided by a dividing wall 14 into two feeding chambers. A molten metal delivery channel 30 and a delivery hole 15 equipped with an adjustable throttle 32 feed a first alloy into a feed chamber and a second metal delivery channel 24 equipped with a side channel, a delivery hole 16 and An adjustable throttle 31 feeds a second alloy into a second feed chamber. Adjustable accelerators 31, 32 are adjusted either manually or in response to some control signal to adjust the metal flow in the respective feed chambers. A vertically movable lower block unit 17 supports an embryonic composite ingot that is being formed and fits into the exit end of the mold before the casting is started and then lowered to allow the ingot to form.

As shown more clearly with respect to Figure 2, in the first feed chamber, the molten metal body 18 gradually cools to form a self-supporting surface 27 adjacent the lower end of the partition wall and then forms a zone 19 which It is between liquid and solid and is often referred to as soft zone. Below this soft or semi-solid zone is a solid metal alloy 20. In the second feed chamber a second liquid alloy stream 21 is fed having a liquidus temperature lower than that of the first alloy 18. This metal also forms a soft zone 22 and possibly a solid portion 23.

The self-supporting surface 27 typically undergoes a slight contraction as the metal separates from the partition wall 14 and then a slight expansion as the displacement forces caused by, for example, the metallostatic pressure of the metal 18, appear. The self-supporting surface has sufficient strength to contain such forces even though the surface temperature may be above the solidus temperature of the metal 18. An oxidized layer on the surface may contribute to this balance of forces. is maintained at a predetermined target temperature by means of a temperature control fluid passing through a closed channel 33 having an inlet 36 and an outlet 37 for delivery and removal of the temperature control fluid which extracts heat from the partition wall. to create a cooled interface that serves to control the temperature of the self-supporting surface 27 below the lower end of the dividing wall 35. The upper surface 34 of the metal 21 in the second chamber is then held at a position below the lower edge 35 of the wall 14 and at the same time the temperature of the self-supporting surface 27 is maintained such that the surface 34 of metal 21 contact this self-supporting surface 27 at a point where surface temperature 27 is between solidus and liquidus temperatures of metal 18. Typically surface 34 is controlled at a point slightly below the lower edge 35 of the partition wall. 14, generally within about 2 to 20 mm from the bottom edge. The interface layer thus formed between the two alloy streams at this point forms a metallurgical binder between the two layers without excessive mixing of the alloys.

The flow (and temperature) of the cooling means required to establish the temperature of the self-sustaining surface 27 of the metal 18 within the desired range is generally determined empirically by the use of small thermoelectric pairs that are embedded in the surface 27 of the metal. metal ingot as it forms and once set for a given melting temperature for metal 18 (melting temperature being the temperature at which metal 18 is delivered to the inner end of the feed chamber) it forms a portion the casting practice for such an alloy. In particular it has been found that at a fixed flow of cooling media through channel 33, the temperature of the cooling medium at outlet 37 correlates well with the temperature of the self-supporting metal surface at predetermined locations below the lower end of the partition wall. and then provides a simple and effective means of controlling this critical temperature by providing a temperature measuring device such as a thermoelectric pair or a thermistor 40 at the channel outlet of the cooling medium.

Figure 3 is essentially the same mold as Figure 1, but in this case a pair of partition walls 14 and 14a is used by dividing the mouth of the mold into three feeding chambers. There is a central chamber for the first alloy and a pair of external feed chambers for a second alloy. The outer feed chambers may be adapted for a second and a third metal alloy, in which case the lower ends of the partition walls 14 and 14a may be positioned differently and the temperature control may differ for the two partition walls depending on the particular needs for each. Casting and creating strongly bonded interfaces between the first and second alloys and between the first and third alloys.

As shown in Figure 4, it is also possible to reverse the alloys so that the first alloy current is fed into the outer feed chambers and a second alloy current is fed into the central feed chamber.

[00104] Figure 5 shows several more complex camera arrangements in plan view. In each of these arrangements there is an outer wall 11 shown for the mold and the inner partition walls 14 separating the individual chambers. Each partition wall 14 between adjacent chambers must be positioned and thermally controlled such that the casting conditions described herein are maintained. This means that the dividing walls can extend downwards from the mold inlet and end in different positions and can be controlled at different temperatures and the metal levels in each chamber can be controlled at different levels according to the needs of the practice. of casting.

It is advantageous to make the partition wall 14 flexible or capable of varying curvature in the mold plane as shown in Figures 6 and 7. The curvature is normally shifted between the starting position 14 'and the steady state position 14 of to maintain a constant interface through casting. This is achieved by means of an arm 25 attached to a top end of the partition wall 14 and directed in a horizontal direction by a linear activator 26. If required the activator is protected by a heat shield 42.

The thermal properties of alloys vary considerably and the amount and degree of variation in curvature is predetermined based on the alloys selected for the various layers in the ingot. These are usually determined empirically as part of the casting practice for a particular product.

As shown in Figure 8 the dividing wall 14 may also be inclined 43 in the vertical direction on the metal side 18. This inclination may vary along the length of the dividing wall 14 to also control the shape of the interface between an alloy layer adjacent. The inclination may also be used on the outer wall 11 of the mold. This inclination or shape may be established using principles, for example as described in U.S. 6,260,602 (Wagstaff) and will again depend on the alloys selected for the adjacent layers.

The dividing wall 14 is made from metal (steel or aluminum, for example), and may in part be made from graphite, for example, by using a graphite insert 46 in the inclined surface. Oil delivery channels 48 and grooves 47 may also be used to provide lubricants or split substances. Naturally oil insertion and delivery embodiments may be used on the outer walls in the manner known in the art.

A particular preferred partition wall embodiment is shown in Figure 9. The partition wall 14 extends substantially parallel to the sidewall of the mold 11 along one or both long faces (lamination) of a rectangular ingot. Near the ends of the long sides of the mold, the dividing wall 14 has 90 ° bends 45 and is terminated at positions 50 on the long side of the side wall 11, rather than extending completely to the short side walls. Ingot coated with such a partition wall can be laminated to better maintain the shape of the coating over the width of the sheet than occurs in more conventional lamination-coating processes. The slope described in Figure 8 can also be applied to this design, where for example a high degree of slope on curved surface 45 and an average degree of slope on straight section 44 can be used.

[00110] Figure 10 shows a method for controlling the level of metal in an ingot mold that can be used in any casting mold, whether for layered or not, but is particularly useful for controlling the metal level in spaces. confined as can be found in some metal chambers in multi-layer ingot casting molds. A gas supply 51 (typically an inert gas cylinder) is attached to a controller flow 52 that delivers a small gas flow to an open-ended gas delivery tube 53 that is positioned at a reference location 54 within the mold. The internal diameter of the gas delivery tube at its outlet is typically between 3 and 5 mm. The reference location is selected to be below the upper surface of metal 55 during the casting operation, and this reference location may vary depending on the needs of the casting practice.

A pressure transducer 56 is attached to the gas delivery tube at a point between the flow controller and the open end to measure the gas back pressure in the tube. Such pressure transducer 56 in turn produces a signal that can be compared to a reference signal for controlling the flow of metal entering the chamber by means known to those skilled in the art. For example, an adjustable refractory plug 57 may be used in a refractory tube 58 fed around a metal delivery 59. In use, the gas flow is adjusted to a low level just sufficient to keep the end of the tube open. gas delivery A piece of refractory fiber inserted into the open end of the gas delivery tube is used to dampen pressure fluctuations caused by bubble formation. The measured pressure then determines the degree of immersion of the open end of the gas delivery tube below the metal surface in the chamber and then the metal surface level with respect to the reference location and the flow rate of the metal in the chamber are therefore. controlled to keep the metal surface at a predetermined position relative to the reference location.

[00112] Flow controller and pressure transducer are commonly available devices. It is particularly preferred however that the flow controller be capable of reliable flow control in the range of 5 to 10 cm 3 / minute gas flow. A pressure transducer capable of measuring pressures up to about 0.689 kPa (0.1 psi) provides a good measure of metal level control (up to about 1 mm) in the present invention and the combination provides good control even when in view of slight fluctuations in pressure caused by slow bubbling through the open end of the gas delivery tube.

[00113] Figure 11 shows a perspective view of a top portion of the mold of the present invention. A feed system for one of the metal chambers is shown to be particularly suitable for feeding the metal into a narrow feed chamber that can be used to produce an ingot coated surface. In this feed system, a channel 60 is provided adjacent to the feed chamber having several small rails 61 attached thereto that terminate below the metal surface. Dispensing bags 62 made of refractory fabric by means known in the art are installed around the outlet of each rail 61 to improve uniformity of distribution and temperature of the metal. The channel is in turn fed from a channel 68 in which a single rail 69 extends into the metal in the channel and into which a flow control cap (not shown) of the conventional design is inserted. The channel is positioned and leveled so that metal flow flows evenly to all locations.

[00114] Figure 12 shows another preferred arrangement of the partition walls 14 for casting a two-sided rectangular cross-section ingot. The partition walls have a straight section 44 substantially parallel to the mold sidewall 11 along one or both long faces of a rectangular cross-section ingot. However, in this case each partition wall has curved end portions 49 that intersect the smaller end wall of the mold at locations 41. This is again useful in maintaining the shape of the coating over the sheet width of what occurs in lamination-coating processes. more conventional. Although illustrated for two-sided casing, it can also be used for single-sided casing of the ingot.

Figure 13 is a 15X magnification photomicrograph showing the interface 80 between an Al-Mn 81 alloy (X-904 containing 0.74 wt% Mn, 0.55 wt% Mg, 0, 3 wt% Cu, 0.17 wt%, 0.07 wt% Si and the balance being Al and the inevitable impurities) and an Al-Si 82 alloy (AA4147 containing 12 wt% Si, 0 , 19% by weight Mg and the balance being Al and the inevitable impurities) melted under the conditions of the present invention. The Al-Mn alloy has a solidus temperature of 1190 * F (643 * 0) and a liquidus temperature of 6570 (1215 ° F). The Al-Si alloy has a solidus temperature of 5760 (1070 ° F) and a liquidus temperature of 5820 (1080 * F). The Al-Si alloy was cast and cast fed so that the upper surface of the metal was kept so that it contacted the Al-Mn alloy at a location where a self-supporting surface was established in the Al-Mn alloy, but its temperature was between the solidus and liquidus temperatures of the Al-Mn alloy.

A clear interface is present in the sample indicating no general mixture of alloys but, in addition, particles of Mn85 containing intermetallic compounds are visible in a range of approximately 200 μηι within the Al-Si 82 alloy adjacent the interface 80 between the alloys. al-Mn and Al-Si alloys. Intermetallic compounds are mainly MnAI6 and α-AIMn.

Figure 14 is a microphotograph at 200X magnification showing interface 80 of the same alloy combination as in Figure 13 where the self-supporting surface temperature was not allowed to fall below the solidus temperature of the Al-Mn alloy before that Al-Si alloy contacted her. A ridge or exudate 88 is observed extending from the interface 80 into an Al-Si 82 alloy from the Al-Mn 81 alloy and the ridge or exudate has an intermetallic composition containing Mn that is similar to the particles in Figure 13. or exudates typically extend up to 100 μΐη in the adjacent metal. The resulting agglutination between the alloys is a strong metallurgical agglutination. Particles of intermetallic compounds containing Mn 85 are also visible in this microphotography and are typically up to 20 µm in size.

[00118] Figure 15 is a microphotograph (at 300X magnification) showing the interface between an Al-Mn alloy (AA3003) and an Al-Si alloy (AA4147) but where the self-supporting Al-Mn surface has been cooled to more than 5 ° C below the solid us temperature of the Al-Mn alloy, at which point the upper surface of the Al-Si alloy contacted the self-supporting surface of the Al-Mn alloy. The agglutination line 90 between the alloys is clearly visible indicating that insufficient metallurgical agglutination has therefore been formed. There is also an absence of dispersed intermetallic exudates or first alloy compositions in the second alloy.

A variety of alloy combinations have been fused according to the process of the present invention. The conditions were adjusted so that the surface temperature of the first alloy was between its solidus and liquidus temperatures on the upper surface of the second alloy. In all cases, the alloys were cast into 690mm x 1590mm ingots and 3 meters long and then processed by conventional preheating, hot rolling and cold rolling. Cast alloy combinations are shown in table 1 below. Using conventional terminology, the "core" is the thickest backing layer in a two-alloy composite and the "coating" is the functional layer of the surface. In the table, the First League is a first cast alloy and the second alloy is the alloy brought into contact with the self-supporting surface of the first alloy. In each of these examples the coating was the first alloy to solidify and the core alloy was applied to the coating alloy at a point where a self-supporting surface was formed but where the surface temperature was still within the LS range given above. This can be compared to the above example for welding sheets where the coating alloy had a lower melting range than the core alloy, in which case the coating alloy (the "second alloy") was applied to the self-supporting surface of the alloy. alloy (the "first alloy"). Microphotographs were taken at the interface between the casing and the core in the four fusions above. Microphotographs were taken at 50x magnification. In each image the "casing" layer appears on the left and the "core" layer on the right.

Figure 16 shows the interface of the N-051804 caster between casing alloy 0303 and core alloy 3104. The interface is clear in changing the grain structure in the passage of the coating material to the relatively higher core layer. on.

Figure 17 shows the interface of the N-030826 caster between casing 1200 and core alloy 2124. The interface between the layers is shown by the dotted line 94 in the figure. In this figure, the presence of alloy 2124 components is present within the grain boundaries of alloy 1200 at a short distance from the interface. These appear as spaced "fingers" of material in the figure, one of which is illustrated by numeral 95. It can be seen that the alloy components 2124 extend over a distance of about 50 pm, which typically corresponds to a single grain of the material. turn on 1200 under these conditions.

Figure 18 shows the interface of casting No. 031013 between casing alloy 0505 and core alloy 6082 and Figure 18 shows the interface of casting No. 030827 between casing alloy 1050 and core alloy 6111. each of these figures the presence of core alloy alloy components is a visible complement within the coating alloy grain boundaries immediately adjacent to the interface.

Claims (3)

1. A method of casting a composite metal ingot comprising at least two layers formed of different alloys, comprising providing an open-ended annular mold having a feed end and an outlet end where the molten metal (18; 21) is added at the feed end and a solidified ingot is extracted from the outlet end, and dividing walls (14, 14a, 14 ') to divide the feeding end into at least two separate feeding chambers, said dividing walls terminating. (35) above said mold exit end, where each feed chamber is adjacent to at least one other feed chamber, where for each pair of adjacent feed chambers a first stream of a first alloy (18) is fed to a chambers of the pair of feed chambers to form a puddle of metal in the first chamber and a second stream of a second alloy (21) is fed through the second chamber of the pair of feed chambers to form a metal puddle in the second chamber, the metal puddles each having an upper surface and the first metal puddle contacts the dividing wall. between the pair of chambers to cool the first to form a self-supporting surface (27) adjacent to the partition wall and the second metal pool is then brought into contact with the first pool so that the second pool initially contacts the surface. self-sustaining first puddle at a point where the temperature of the self-sustaining surface characterized by being between the solidus and liquidus temperatures of the first alloy; the second alloy must contact the first alloy below the lower end (35) of the partition wall (14, 14a, 14 ') from 2 mm to 20 mm, the temperature of the partition wall (14, 14a, 14') being maintained at a predetermined target temperature by means of a temperature control fluid passing through a closed channel (33) having an inlet (36) and an outlet (37) for delivery and removal of temperature control fluid from the partition wall (14). 14a, 14 ') to create a cooled interface that controls the temperature of the self-supporting surface (27) below the lower end (35) of the partition wall (14, 14a, 14), and the partition walls to divide the feeding end are flexible and the shape of the partition walls (14, 14a, 14) is adjusted during the casting process, the two alloy streams being joined as two layers (20, 23) and cooling the joined alloy layers to form a composite metal ingot having a the totally uniform interface. Casting apparatus for producing composite metal ingots according to the method defined in claim 1, comprising an open-ended annular die (10) having a feed end and an outlet end and a movable lower block (17) adapted to fit within the outlet end and movable along the axis of the annular mold (10), where the mold feed end is divided into at least two separate feed chambers, each feed chamber being adjacent to one another. at least one other feed chamber, and where adjacent pairs of feed chambers are separated by a partition wall (14, 14a, 14) terminating above the mold exit end, characterized in that the partition wall (14, 14a 14 ') is flexible and is provided with one or more linear activators (26) and control arms (25) attached to the partition wall to allow the shape of the wall (14, 14a, 14) is varied during the casting operation and maintained at a predetermined target temperature by a temperature control fluid passing through a closed channel (33) having an inlet (36) and a outlet (37) for delivery and removal of temperature control fluid from the partition wall (14, 14a, 14), Composite metal ingot obtained by the method defined in claim 1, characterized in that it comprises at least two alloy layers of different compositions, wherein pairs of adjacent layers consisting of a first alloy and a second alloy are formed by applying the second alloy to each other. a molten state on the surface of the first alloy while the surface of the first alloy is at a temperature between the solidus and liquidus temperatures of the first alloy, the two alloy streams being joined as two layers (20, 23) and cooling the layers of alloys joined to form a composite metal ingot having a fully uniform interface.