KR20050058402A - Casting of non-ferrous metals - Google Patents

Abstract

A method of continuous casting non- ferrous alloys which includes delivering molten non-ferrous alloy (M) to a casting apparatus. The casting apparatus rapidly cools at least a portion of the non-ferrous alloy at a rate of at least about 100 °C thereby solidifying an outer layer (6, 8) of the non-ferrous alloy surrounding an inner layer (16) of a molten component and a solid component of dendrites (14). The dendrites (14) are altered to yield cast product exhibiting good resistance to cracking.

Description

Casting method of nonferrous metals {CASTING OF NON-FERROUS METALS}

FIELD OF THE INVENTION The present invention relates to the casting of nonferrous metal alloys and, more particularly, to casting nonferrous metal alloys, including rapidly solidified shells and broken dendrites, to create a central zone that is not segregated.

Continuous casting of metals such as aluminum alloys is typically carried out in twin roll casting machines, block casting machines, belt casting machines. Twin roll casting machines of aluminum alloys have excellent performance and commercial applications despite the relatively low production speeds achievable recently. Twin roll casting is a combination of solidification and deformation techniques that typically involves supplying molten metal into the bite between a pair of opposing and rotating cold rolls where solidification begins when the molten metal contacts the roll. The solidified metal forms a “freeze front” of the molten metal in the roll bite and the solid metal advances to the nip, the minimum clearance point between the rolls. The solid metal passes through the nip with a solid sheet. The solid sheet is deformed (hot rolled) by the roll to exit the roll.

The aluminum alloy is continuously roll cast to 50-70 pounds per hour (lbs / hr / in) for a width of 1 inch or to 1/4 inch thick sheets at about 4-6 feet per minute. Attempts to increase the speed of roll casting generally fail because of segregation in the center. Although it is recognized that thin sheets (eg less than 1/4 inch) can be produced faster than thick sheets, the ability to roll cast aluminum is achieved at speeds significantly higher than about 70 (lbs / hr / in). It's hard to do.

Typical operation of a thin thickness twin roll casting machine is disclosed in US Pat. No. 5,5518,064, incorporated herein by reference and shown in FIGS. 1 and 2. The molten metal holding chamber H is connected to a supply tip T for distributing the molten metal M between the water-cooled pair rolls R1 and R2 which respectively rotate in the directions of the arrows A1 and A2. The rolls R1 and R2 have smooth surfaces U1 and U2, and the roughness of the surface is a product of the roll grinding technique employed at the time of roll manufacture. The centerline of the rolls R1, R2 is in a vertical or generally vertical plane L such that the casting strip S forms a generally horizontal path (eg from vertical to about 15 °). Another form of this method produces a strip in the vertical direction. The width of the casting strip S is determined by the width of the tip T. The plane L passes through the region of minimum clearance between the rolls R1 and R2 called roll nips N. The solidification zone exists between the solid casting strip S and the molten metal M and comprises a liquid-solid mixing zone X. Solidification front F is defined between the region X and the casting strip S which is a line of complete solidification.

In a conventional roll casting of aluminum alloy, the heat of molten metal M is transferred to the rolls R1 and R2 so that the position of the solidification front F is maintained upstream of the nip N. In this way, the molten metal M solidifies to a thickness larger than the dimension of the nip N. The solid cast strip S is deformed by the rolls R1 and R2 to achieve the final strip thickness. Hot rolling of strips solidified between rolls R1 and R2 according to conventional roll casting exhibits unique properties to the strip properties of roll cast aluminum alloy strips. In particular, the central region of the strip thickness is enriched in process forming elements such as Fe, Si, Ni, Zn in the alloy and depletion of the pore forming elements Ti, Cr, V, Zr. This enrichment of process forming elements (ie alloying elements other than Ti, Cr, V, Zr) in the central zone corresponds to the solidification front (F) known as central segregation where the part of the strip (S) finally solidifies. Because. Excessive center segregation in the casting strip is a factor that limits the speed of conventional roll casting machines. Casting strips also show signs of machining by rolls. The particles formed upon solidification of the metal upstream of the nip are flattened by the rolls. Therefore, the roll cast aluminum includes the particles drawn at an angle with respect to the rolling direction.

The roll gap in the nip N can be reduced to produce a thinner strip S. However, the roll separation force generated by the solid metal between the rolls R1 and R2 increases when the roll gap is reduced. The magnitude of the roll separation force is influenced by the position of the solidification front F relative to the roll nip N. When the roll gap is reduced, the reduction rate of the metal sheet is increased and the roll separation force is increased. At some point the relative position of the rolls R1 and R2 to achieve the desired roll gap cannot overcome the roll separation force and the minimum thickness is at the position of the solidification front F.

Roll separation force can be reduced by increasing the speed of the roll to move the solidification front F downstream to the nip N. When the solidification front is moved downstream (toward the nip N), the roll gap can be reduced. This movement of the solidification front F reduces the ratio between the thickness of the strip at the initial solidification time and the roll gap in the nip N, thus reducing the roll separation force in proportion to the less solidified metal being compressed and hot rolled. Decrease. In this way proportionally more metal is solidified and then hot rolled to thinner dimensions as the position of the solidification front F moves towards the nip N. According to the conventional method, roll casting of a thin thickness strip first rolls a strip of relatively large dimension, reduces the dimension until the maximum roll separation force is reached, advances the solidification front to lower the roll separation force (roll By increasing the speed) again until the maximum roll separation force is reached, by repeating the process of advancing solidification forward and reducing the dimension in an iterative manner until the desired thin dimension is achieved. For example, the thickness can be reduced (eg 6 millimeters) until the 10 millimeter strip S is rolled and the roll separation force is excessive, requiring a roll speed increase.

The process of increasing the roll speed can only be carried out until the solidification front F reaches a predetermined downstream position. The conventional approach is described as the solidification front F does not advance forward of the roll nip N to ensure that the solid strip is rolled in the nip N. Roll the solid strip in the nip (N) to prevent breakage of the hot rolled cast metal strip (S) and to provide sufficient tensile strength to the exiting strip (S) to withstand the tension of downstream winders, pinch rolls, and the like. It was generally recognized that there was a need to do so. As a result, the roll separation force of a twin roll casting machine, which is usually operated in a solid strip of aluminum alloy hot rolled in the nip N, is on the order of several tons per inch of width. Although some reduction is possible, operation at this high roll separation force makes it very difficult to further reduce the strip thickness to ensure deformation of the strip in the nip N. The speed of the roll casting machine is limited by the requirement to keep the solidification front F upstream of the nip N and to prevent center segregation. Therefore, the roll casting speed for the aluminum alloy was relatively low.

A reduction in roll separation force to obtain acceptable microstructure in aluminum alloys with high alloying element concentrations is disclosed in US Pat. No. 6,193,818, incorporated herein by reference. Alloys containing 0.5 to 13 weight percent Si are roll cast into strips of about 0.05 to 0.2 inches at a roll separation force of about 5000 to 40,000 at a rate of about 5 to 9 feet per minute. While this represents an advance in reducing roll separation, this separation still implies significant process improvements. In addition, productivity remains compromised and strips produced in accordance with US Pat. No. 6,193,818 exhibit significant central segregation and particle elongation as shown in FIG. 3 of the publication.

A major obstacle to high speed roll casting is the difficulty in achieving uniform heat transfer in the molten metal to the smooth surfaces U1, U2, ie cooling the molten metal. In practice, surfaces U1 and U2 contain various defects that change the heat transfer characteristics of the roll. At high roll speeds, this heat transfer nonuniformity is a problem. For example, regions of the surfaces U and U2 where proper heat transfer takes place cool the molten metal M upstream of the nip N at a given location, while regions with insufficient heat transfer characteristics may have a portion of the molten metal. Allow for advancing beyond the position creating non-uniformity in the casting strip.

The thin steel strip was successfully roll cast in a vertical casting machine at high speed (up to about 400 feet per minute) and low roll separation force. Since the rolls of the vertical roll casting machine are located side by side, the strip is formed in the downward direction. In this vertical orientation, the molten steel is led to the bite between the rolls forming the molten steel pool.

Vertical twin roll casting from molten metal pools is successful for steel, but vertical casting of oxidation sensitive alloys (eg aluminum) requires additional control. One proposal to overcome the problem of aluminum being oxidized in laboratory-level vertical roll casting is described by Haga et al., "High Speed Roll Casting Machine for Aluminum Alloys," Proceedings of ICAA-6, Aluminum Alloys, Vol. 1, pp. 327-332 (1998). According to the method, the strip of molten aluminum alloy is discharged directly from the gas press nozzle to one or both pairs of pairs of vertical roll casting machines. Although high speed casting of aluminum alloy strips has been reported, a major drawback of this technique is that the release rate of the molten aluminum alloy must be carefully controlled to ensure uniformity in the casting strips. When a single stream exits the roll, the stream solidifies into a strip. If the stream is discharged on each roll, each stream becomes a half-thick cast strip. In both cases, a change in the release rate or gas pressure of the molten aluminum alloy results in nonuniformity of the casting strip. Control parameters for this type of aluminum alloy roll casting are not practical for commercial devices.

At a speed of about 20-25 feet per minute at a thickness of about 3/4 inch (19 mm) reaching a productivity level of about 1400 (lbs / hr / in), continuous casting of aluminum alloys was achieved in a belt casting machine. In conventional belt casting as disclosed in US Pat. No. 4,002,197, incorporated herein by reference, molten metal is fed into the casting region between opposite portions of a pair of rotating flexible metal belts. Each flexible casting belt rotates in a defined path between an upstream roller disposed at one end of the casting zone and a downstream roller disposed at the other end of the casting zone. In this way, the casting belts converge to directly face each other around the upstream roller to form an inlet in the casting region of the nip between the upstream rollers. Molten metal is fed directly into the nip. As it is moved along the belt, the molten metal is confined and solidified between the moving belts. Heat released by the solidified metal escapes through two belt portions adjacent to the metal being cast. This heat is released by rapidly moving a film of substantially continuous water that is in communication with the opposite surface of the belt and thereby cools the opposite surface of the belt.

The operating parameters for belt casting are quite different from those for roll casting. Indeed, there is no intentional hot rolling of the strip. Solidification of the metal to a thickness of 3/4 inch is completed at a distance of about 12-15 inches (30-38 mm) downstream of the nip. The belt is exposed to high temperatures when molten metal is contacted on one surface and cooled by water on the inner surface. This can cause deformation of the belt. In order to achieve a consistent surface quality of the strip, the tension of the belt must be adjusted to account for the expansion or contraction of the belt due to temperature changes. Casting of aluminum alloys in belt casting machines has been used until recently, mainly for products that require minimal quality surfaces or for painted products.

The problem of thermal instability of the belt is avoided in block casting machines. The block casting machine includes a plurality of quench blocks mounted adjacent to each other on a pair of opposing tracks. Each set of quench blocks rotates in opposite directions to form a casting region through which molten metal is guided therebetween. The quench block acts as a heat sink through which heat of molten metal is transferred. Solidification of the metal at 3/4 inch thick is completed about 12-15 inches downstream of the inlet of the casting zone. Heat transferred to the quench block is removed during the return loop. Unlike the belt, the quench block is not deformed by heat transfer. However, block casting machines require precise dimensional control to prevent gaps between blocks causing unevenness and defects in the casting strips.

This concept of transferring heat of molten metal to the casting surface has been used in an improved belt casting machine as disclosed in US Pat. Nos. 5,515,908 and 5,564,491, incorporated herein by reference. In a heat sink belt casting machine, the molten metal is led to a belt (cast surface) upstream of the nip where solidification begins before the nip and heat transfer continues from the metal to the belt downstream of the nip. In this system, the molten metal is fed to the belt along the curve of the upstream rolls so that the metal solidifies substantially until the time of reaching the nip between the upstream rolls. The heat of the molten metal and the casting strip is transferred to the belt in the casting area (including downstream of the nip). The heat is then removed from the belt while the belt is in contact with either the molten metal or the cast strip. In this way the belt portion in the casting zone does not experience the large temperature changes that occur in conventional belt casting machines. The thickness of the strip can be limited by the heat capacity of the belt where the casting takes place. A production rate of 2400 (lbs / hr / in) was achieved for a 0.08-0.1 inch (2-2.5 mm) strip of thickness.

However, problems associated with belts used in conventional belt castings persist. In particular, the non-uniformity of the cast strip depends on the stability of the belt (ie the tension of the belt). In a conventional or heat sink type belt casting machine, the contact of the belt with the hot molten metal and heat transfer from the solidified metal to the belt creates instability in the belt. In addition, the belts must be discontinued and replaced regularly.

Strip materials of non-ferrous alloys are preferred for use as sheet products in the automotive and aerospace industries and in the manufacture of can bodies and can ends and tabs. Conventional manufacture of can bodies employs batch processes that involve extensive sequential procedures of individual steps. When ingots are needed for the process, the ingots are first heat treated to scalp the surface and homogenize the alloy, rolled in multiple passes in a cooled and still hot condition, finished hot rolled, finally coiled and cold Are kept. The coil may be annealed in a placement step. The coil sheet is then further reduced to final dimensions by cold rolling using a coil unwinder, coil rewinder, single and / or tandem rolling mill. This batch process is generally used in the aluminum industry, which requires different and much material handling operations to move the ingots and coils between separate processes.

 Performance on flow production of can bodies is disclosed in US Pat. No. 4,260,419 through direct quench casting and US Pat. No. 4,282,044 via small scale continuous strip casting. This process requires a lot of material handling work to move the ingots and coils. This work leads to excessive labor, energy consumption and product damage.

U.S. Pat.Nos. 5,772,802 and 5,772,799, incorporated herein by reference, disclose a belt casting method of cans or lids and a manufacturing method of strip casting such that a low alloy concentration aluminum alloy forms a hot strip casting raw material, the raw material being subjected to substantial precipitation. It is quenched quickly to prevent, annealed and quenched to prevent substantial precipitation of the alloying elements, and then cold rolled. This process has been successful until recently despite the relatively low production rates achievable.

In addition, other alloys, such as magnesium alloys other than aluminum, have not been continuously cast on a commercial scale. Magnesium metal has a hexagonal structure that significantly limits the amount of deformation that can be applied, especially at low temperatures. The production of the working magnesium alloy product is therefore usually carried out by hot working at 300-500 ° C. Under these conditions, a plurality of rolling passes and intermediate annealing treatments are required. In a conventional method, up to 25 total rolling passes are used with intermediate annealing to make a 0.5 mm thick final product. As a result, the price of magnesium processed products is high.

Thus, there is still a need for a low cost method of casting nonferrous alloys that achieves uniformity on the casting surface.

1 is a partial schematic view of a casting machine having a molten metal discharge tip and a pair of rolls;

2 is an enlarged cross-sectional view of the molten metal release tip and roll shown in FIG. 1 operated according to the prior art;

3 is a flowchart of the casting method of the present invention;

4 is a schematic view of a molten metal casting operated in accordance with the present invention;

5 is a schematic view of a casting machine made according to the invention with a strip support mechanism and optional cooling means; And

6 is a schematic view of a casting machine made in accordance with the present invention with another strip support mechanism and optional cooling means.

This demand is due to the release of molten nonferrous alloys on a pair of spaced cast surfaces and to rapidly solidify a portion of the nonferrous alloys at a rate of at least about 100 ° C. per minute, thereby enclosing the nonferrous alloys surrounding the solid and molten components of the dendrite. It is solved by the nonferrous alloy solidification method of the present invention which includes solidifying the outer layer. Suitable alloys include aluminum alloys, magnesium alloys and titanium alloys. The outer layer that solidifies when the alloy is cast increases in thickness. When the inner layer solidifies, the dendrite of the inner layer is altered by breaking or separating the dendrites into smaller tissues. The product exiting the casting apparatus includes a solid inner layer with altered dendrite (substantially avoided or minimized center segregation) surrounded by an outer solid layer of the alloy. Depending on the casting device, the product may be in the form of sheets, plates, slabs, foils, wires, rods, bars and the like. Suitable final products include automotive sheet products, aircraft seat products, beverage can body raw materials and beverage can end and tab raw materials.

The casting surface may be a roll surface in a roll casting machine or a belt surface in a belt casting machine or conventional spaced casting surfaces approaching each other. Solidification of the semisolid layer is completed at the location of the minimum distance between the casting surfaces. In one embodiment, the casting surface is the surface of a rotating roll with a nip defined therebetween, and completion of the solidification step occurs at the nip. The force applied by the rolls on the metal advancing in between is up to about 300 pounds per inch of width of the product. In another embodiment, the casting surface is the surface of the belt running over the rotating rolls, the rolls forming a nip between them, and the completion of the solidification step occurs at the nip. The solidified product with the inner layer exits the location of the minimum distance between the casting surfaces at a speed of about 25 to about 400 feet per minute, or at least about 100 feet per minute.

The invention includes products produced according to the method of the invention. The product may be in the form of a metal strip having a thickness of about 0.06 to about 0.25 inches. The thickness of the inner layer may constitute about 20 to about 30 percent of the strip thickness. One result of the method of the present invention is that the composition of the solidified inner layer of metal differs from that of the outer layer of metal. In addition, the broken dendrite of the inner layer of metal remains in the form of a sphere (unprocessed).

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be clearly understood from the following detailed description taken in conjunction with the accompanying drawings, wherein like reference numerals identify like parts.

For the purposes of the following description, the invention is contemplated of various modifications and sequences of steps, except where expressly specified. Also particular apparatus and processes illustrated in the accompanying drawings and described below are exemplary embodiments of the present invention. Therefore, specific dimensions and other physical characteristics relating to the embodiments disclosed herein should not be considered as limiting. When referring to any numerical range value, it is understood that this figure includes each and every value and / or decimal value between the minimum and maximum of the stated range.

The present invention includes a method of casting a nonferrous alloy that includes releasing a molten nonferrous alloy into a casting device. By non-ferrous alloy is meant an alloy of elements such as aluminum, magnesium, titanium, copper, nickel, zinc or tin. Particularly suitable nonferrous alloys for use in the present invention are aluminum alloys, magnesium alloys and titanium alloys.

"Aluminum alloy", "magnesium alloy" and "titanium alloy" mean an alloy comprising at least 50% of the mentioned elements and at least one modifying element. Aluminum, magnesium and titanium alloys are attractive alloys for structural applications in the aviation and automotive industries because of their light weight, high strength-to-weight ratio, high stiffness at room temperature and high temperatures. Suitable aluminum alloys include AA 3xxx based and 5xxx based alloys. Examples of magnesium alloys include Mg-Al alloys, Mg-Al-Zn alloys, Mg-Al-Si alloys, Mg-Al-RE (Rare Earth) alloys, Mg-Th-Zr alloys, Mg-Th-Zn-Zr alloys, Mg-Zn-Zr alloy and Mg-Zn-Zr-RE alloy.

The invention in its most basic form is schematically illustrated in the flowchart of FIG. In step 100, the molten nonferrous metal is discharged to the casting apparatus. The casting apparatus includes a pair of spaced apart rotating casting surfaces as described in detail below. In step 102, the casting apparatus rapidly cools at least a portion of the nonferrous alloy to solidify the outer layer of the nonferrous alloy while maintaining the semisolid inner layer. The inner layer comprises the solid component of the metal dendrites and the molten metal component. The outer layer that solidifies when the alloy is cast increases in thickness. The dendrites of the inner layer are changed in step 104 by breaking the dendrites into smaller tissues. The product exiting the casting apparatus includes a solid inner layer formed in step 106 comprising broken dendrite sandwiched in an outer solid layer of the alloy. The product may be in various forms such as, but not limited to, sheets, plates, slabs, foils. In extrusion casting, the product may be in the form of a wire, rod, bar or other form. In either case, the product may be further processed and / or processed at step 108. The order of steps 100-108 is not fixed in the method of the present invention and may occur sequentially or certain steps may occur simultaneously.

The present invention harmonizes the solidification rate of the molten metal, the formation of dendrites in the solidified metal and the modification of the dendrites in order to obtain the desired properties in the final product. The cooling rate is chosen to achieve rapid solidification of the outer layer of metal. In aluminum alloys and other nonferrous alloys, cooling of the outer layer of metal occurs at a rate of at least about 100 ° C. per minute. Suitable casting apparatuses include cooled casting surfaces such as in twin roll casting machines, belt casting machines, slab casting machines or block casting machines. Vertical roll casting machines can also be used in the present invention. In a continuous casting machine, the casting surface generally has an area that is spaced apart and the distance between them is minimal. In roll casting machines, the area of the minimum distance between the casting surfaces is the nip. In a belt casting machine, the area of the minimum distance between the casting surfaces of the belt may be the nip between the inlet pulleys of the casting machine. As explained in more detail below, the operation of the casting apparatus in the manner of the present invention involves the solidification of the metal at the location of the minimum distance between the casting surfaces. Although the method of the present invention is described below as being performed using a twin roll casting machine, this does not mean to be limiting. Other continuous casting surfaces can be used to practice the invention.

For example, a roll casting machine (FIG. 1) can be operated to practice the invention as shown in detail in FIG. 4. Referring to FIG. 1 (approximately illustrating a horizontal continuous casting in accordance with the prior art and the present invention), the present invention provides a pair of opposing rotating cooling rolls R1 and R2 that each rotate in the direction of arrows A1 and A2. Is executed using). The term horizontal means that the casting strip is produced in the horizontal direction, or at an angle of about 30 ° up or down from the horizontal. As shown in more detail in FIG. 3, the feed tip T made of refractory material or other ceramic material is directed in the direction of arrow B directly to the rolls R1 and R2 which respectively rotate in the direction of arrows A1 and A2. The molten metal (M) is distributed by The feed tip T and each to minimize the exposure of the molten metal to the atmosphere along the rolls R1 and R2 while preventing leakage of the molten metal and avoiding contact between the tip T and the rolls R1 and R2. The gaps G1 and G2 between the rolls R1 and R2 are kept as small as possible. Suitable dimensions of the gaps G1 and G2 are about 0.01 inch (0.25 mm). The plane L passing through the center of the rolls R1 and R2 passes through the region of the minimum clearance between the rolls R1 and R2 referred to as the roll nip N.

Molten metal M is supplied to a cooling surface of the roll casting machine, that is, cold rolls R1 and R2. Molten metal M is in direct contact with rolls R1 and R2 in regions 2 and 4, respectively. Upon contact with the rolls R1, R2, the metal M cools and starts to solidify. The metal to be cooled solidifies with an upper shell 6 of solidified metal adjacent to roll R1 and a lower shell 8 of solidified metal adjacent to roll R2. The thickness of the shells 6, 8 increases as the metal M advances toward the nip N. Large dendrites 10 of solidified metal are produced at the interface between the molten metal M and the respective upper and lower shells 6, 8. Large dendrites 10 are broken and attracted into the central portion 9 of the slower moving flow of molten metal M and carried in the direction of arrows C1, C2. The attraction of the flow causes the large dendrites 10 to break into smaller dendrites 14. In the central portion 12 upstream of the nip N represented by the region 16, the metal M is semisolid and comprises a solid component (small solidified dendrites 14) and a molten metal component. The metal M in the region 16 has a thick concentration due in part to the dispersion of the small dendrites 14 therein. At the position of the nip N, some molten metal is pressed back in the opposite direction to the arrows C1, C2. The forward rotation of the rolls R1 and R2 in the nip N substantially forces the molten metal in the central portion 12 upstream from the nip N such that the metal is completely solid when the metal leaves the point of the nip N. Only the solid portion of the metal (small dendrites 14 and upper and lower shells 6 and 8 of the central portion 12) is advanced. Downstream of the nip N, the central portion 12 is a solid intermediate layer comprising small dendrites 14 sandwiched between the upper shell 6 and the lower shell 8. In the middle layer 18, the small dendrites 14 are about 20 to about 50 microns in size and have a generally spherical shape. In strip products, the solid inner portion consists of about 20 to about 30 percent of the total thickness of the strip. Although the casting machine of FIG. 4 is shown to produce a strip S in a generally horizontal direction, this does not mean that the strip is limited to exiting the casting machine at an angle or vertically.

The casting process described in connection with FIG. 4 follows the method steps described above. The molten metal released to the roll casting in step 100 begins to cool and solidify in step 102. The metal to be cooled appears as the outer layers 6, 8 of solidified metal near or near the cooled casting surfaces R1, R2. The solidified layers 6, 8 increase as the metal advances through the casting apparatus. By step 102, dendrites 10 are formed in the metal of the inner layer 12 which is at least partially surrounded by the solidified outer layers 6, 8. In FIG. 4, the outer layers 6, 8 substantially surround the inner layer 12 as a sandwich of the inner layer between the two layers 6, 8. In other casting devices it is also possible that the outer layer completely surrounds the inner layer. In step 104, the dendrites 10 break and change into small tissue 14, for example. In the inner layer 12 prior to complete solidification of the metal, the metal is semisolid and comprises a solid component (small solidified dendrites 14) and a molten metal component. At this stage the metal has a thick concentration due in part to the dispersion of small dendrites 14 therein. In step 106 of the complete solidification position of the metal in the casting apparatus, the solidified product comprises an inner portion 18 comprising a small dendrite 14 at least partially surrounded by an outer portion. The thickness of the inner portion can be about 20 to about 30 percent of the product thickness. In the inner portion, the small dendrites are about 20 to about 50 microns in size and are not substantially processed by the casting device and have a generally spherical shape.

According to the invention, the molten metal of the inner layer 12 is pressed in the direction opposite to the flow direction through the casting device (as described with reference to casting between rolls) and / or the outer layers 6, 8. It can be forced into and reach the outer surface of the outer layers 6, 8. The property of pressing and / or forcing molten metal to the inner layer takes place in the casting apparatus described herein.

The breaking of the dendrites of the inner layer in step 104 during casting between the rolls is achieved by the shear force resulting from the difference in velocity between the inner and outer layers of molten metal. Roll casting machines operated at typical speeds of less than 10 feet per minute do not produce the shear forces necessary to break these dendrites. While the high speed operation (at least 25 feet per minute) of a conventional roll casting machine with solidification control as described above allows casting in the manner of the present invention, other conventional casting apparatuses also operate in a manner that represents the process of the present invention. Can be adapted. An important aspect of the present invention is the breaking of dendrites in the inner layer. Breaking of dendrites minimizes or avoids center segregation and exhibits improved formability and stretching properties in the final product due to the reduction or absence of coarse compositions present in conventional roll casting or belt cast products having center segregation. Other suitable mechanisms for breaking the dendrites of the inner layer include mechanical agitation of liquids (eg propellers), electromagnetic agitation including rotary stator agitation and linear stator agitation, and application to high frequency ultrasonic vibrations.

The casting surface serves as a heat sink for the heat of the molten metal. In the present invention, heat is transferred from the molten metal to the cooled casting surface in a uniform manner to ensure uniformity on the surface of the cast article. The cooled casting surface may be made of steel or copper and includes surface irregularities in contact with the molten metal. Surface irregularities serve to increase heat transfer at the surface of the cooled cast surface. Control over the degree of surface unevenness of the cooled cast surface can result in uniform heat transfer across the surface. The surface irregularities can be grooves, dimples, knurled surfaces or other forms and are spaced in a regular pattern with about 20 to 120 nonuniformities per inch or about 60 nonuniformities per inch. Surface irregularities can have a height of about 5 to 50 microns or about 30 microns. The cooled cast surface may be coated with a material such as chromium or nickel to enhance separation of the cast product.

In general, the casting surface tends to be heated at the time of casting and oxidized at high temperatures. Uneven oxidation of the casting surface during casting can change the heat transfer properties of the casting surface. Therefore, the casting surface can be oxidized before use to minimize the change of the casting surface during casting. Sometimes or continuously brushing the casting surface is advantageous in removing debris formed during casting of the nonferrous alloy. Small pieces of the cast product can break from the product and attach to the cast surface. These small pieces of nonferrous alloy products are susceptible to oxidation, resulting in nonuniformity in the heat transfer properties of the cast surface. Brushing the casting surface prevents non-uniformity problems caused by debris that may collect on the casting surface.

In a roll casting machine operated in the manner of the present invention, the selection, maintenance and control of the appropriate speeds of the rolls R1 and R2 can affect the operation of the present invention. The roll speed determines the speed at which the molten metal M advances toward the nip N. If the speed is too slow, the large dendrites 10 do not receive sufficient force to enter the central portion 12 and break into small dendrites 14. Thus, the present invention is suitable for operating at high speeds, such as about 25 to 400 feet per minute or 100 to 400 feet per minute or about 150 to about 300 feet per minute. The linear speed per unit area at which molten aluminum is released to the rolls R1 and R2 may be less than the speed of the rolls R1 and R2 or about one quarter of the roll speed. High speed continuous casting according to the invention can be achieved in part because the woven pattern surfaces D1 and D2 ensure uniform heat transfer from the molten metal M.

Roll separation force is an important parameter for practicing the present invention. An important advantage of the present invention is that no solid strip is produced until the metal reaches the nip (N). The thickness is determined by the dimensions of the nip N between the rolls R1 and R2. Since the roll separation force is large enough, the molten metal is pressed upstream away from the nip (N). Excess molten metal passing through the nip N causes the layers of the upper and lower shells 6, 8 and the solid central portion 18 to be far from each other and cause misalignment. Insufficient molten metal reaching the nip N causes premature formation of the strip as occurs in conventional roll casting processes. The strip 20 formed in the early state is deformed by the rolls R1 and R2 and has a center segregation. Suitable roll separation force is about 25 to about 300 pounds per inch wide or about 100 pounds per inch wide. In general, slower casting speeds are required to remove heat from thick alloys when casting thicker nonferrous alloys. Unlike conventional roll casting, this slow casting speed does not result in excessive roll separation in the present invention because no solid iron strip is produced upstream of the nip.

Non-ferrous alloy strips may be produced at a thickness of about 0.1 inches or less (eg 0.06 inches) at a casting speed of about 25 to about 400 feet per minute. In addition, using the method of the present invention, for example, about 0.25 inch thick non-ferrous alloy strip can be produced. Casting at the linear speeds (ie, about 25 to about 400 feet per minute) attempted by the present invention solidifies the nonferrous alloy product about 1000 times faster than nonferrous alloy castings such as ingots and outperforms nonferrous alloy castings such as ingots. Improve properties.

The invention also comprises a nonferrous alloy product according to the invention. The nonferrous alloy article includes an inner portion that is substantially surrounded by the outer portion. The concentration of alloying elements may differ between the inner and outer parts. The molten alloy may have an initial concentration of alloying elements, including well-formed alloying elements and process forming alloying elements. The concentration of the alloying element may be different between the outer part and the inner part. The inner part of the product may be depleted of certain elements (process forming elements) and enriched in others (compound forming elements) as compared to the concentrations of the process forming and trap forming elements in the metal and the outer parts, respectively. The crystals of the nonferrous alloy product of the present invention have a substantially undeformed state, that is, an equiaxed structure, for example spherical. The absence of hard particles in the interior parts of the product minimizes or avoids the central segregation and cracking common in most cast nonferrous alloys.

In practicing the present invention, it may be advantageous to support the product exiting the casting apparatus until the product is cooled sufficiently to support itself. The support mechanism shown in FIG. 5 comprises a continuous conveyor belt B positioned under the strip S exiting the rolls R1, R2. Belt B moves around pulley P and supports strip S over a distance of about 10 feet. The length of the belt B between the pulleys P is determined by the casting process, the outlet temperature of the strip S and the alloy of the strip S. Suitable materials for the belt B include fiberglass, metal in solid form (eg steel) or mesh. Alternatively, as shown in FIG. 6, the support mechanism may comprise a stationary support surface J, such as a metal shoe, in which the strip moves over while cooling. The shoe J may be made of a material in which the hot strip S does not easily stick. If the strip S is damaged when it exits the rolls R1 and R2, the strip S can be cooled with a fluid such as air or water at the location E. Typically for aluminum alloys, strip S exits rolls R1 and R2 at about 1000 ° F., and it is desirable to lower the aluminum alloy strip temperature to about 1000 ° F. in a nip N of about 8 to 10 inches. Do. One suitable mechanism for cooling the strip at position E to achieve this degree of cooling is disclosed in US Pat. No. 4,823,860, which is incorporated herein by reference.

Yes

Aluminum alloys containing by weight 0.75 Si, 0.20 Fe, 0.80 Cu, 0.25 Mn, 2.0 Mg were subsequently hot rolled and cold rolled to a thickness of 0.015 inches after being cast in accordance with the present invention. The final characteristics for both products are listed in Table 1. Example 1 has shown the characteristic obtained in the state rolled after coil cooling. The combination of high strength and good moldability (stretching) is noteworthy. The combination of high yield strength and elongation obtained in Examples 1 and 2 has not previously been achieved with 5xxx-based Al-Mg alloys. In comparison, the best 5182 aluminum alloy has a yield strength of 54 ksi and an elongation of 7%. Example 2 shows the properties obtained after the sheet was solution treated in the laboratory and aged at 275 ° F. Excellent yield strength and excellent bending properties have been achieved.

characteristic Example 1 Example 2 Yield strength (ksi) 60 43 Tensile strength (ksi) 65 55 Elongation (%) 10 16 Bending radius (r / t) 1.7 0.3 (flat boundary) Luther's band none none Olsen height (in) -lubrication 0.195 Not applicable corrosion Not applicable Not applicable Orange peel none none Wrap-up Semi-gloss Rolling state O-heat treatment practice practice

By practicing the method of the present invention, non-ferrous cast alloy articles can be produced with improved yield strength and elongation compared to conventional cast articles. This improved property allows the production of thinner products that are commercially desirable.

The product exiting the casting apparatus can then be molded into other forms by rolling or the like or processed to produce can sheets, tab stock, automotive sheets and other final products including lithographic sheets and glossy sheets. Subsequent processing of the product exiting the casting apparatus may be carried out by rolling immediately immediately in order to benefit from the heat of the cast sheet (US Pat. Nos. 5,772,799; 5,772,802; 5,356,495; 5,496,423; 5,514,228; 5,470,405, incorporated herein by reference). ; According to 6,344,096 and 6,280,543). Alternatively, the cast sheet can be cooled and then rolled in a separate process. Other processes of the sheet can be carried out in accordance with one or more of the above patents.

While the preferred embodiments of the present invention have been described as particularly useful in producing non-ferrous alloys for the automotive and aviation industry and the beverage can industry, the present invention also relates to boards, canoes, skis, pianos, harps, transport truck bodies, truck caps, Buses, waste collection containers, racing boat hulls, personal aircraft, fire truck hose containers, material handling equipment, dockboards, mobile lamps, aerospace equipment components including rockets and satellites, radar tracking devices, electrical equipment cabinets, vibrating screens, transport containers It is apparent to those skilled in the art that it is useful for producing parts such as luggage frames and sides, ladders, water heater anodes, typewriters, rocket launchers and mortar bases, weaving parts, concrete buckets and manual finishing tools, jigs, fixtures and vibration inspection devices. Do.

While preferred embodiments of the present invention have been described as being particularly useful for horizontal casting of nonferrous alloys, it will be apparent to those skilled in the art that the present invention is also useful for casting at any angle between vertical and horizontal casting as well as vertical casting.

Although the preferred embodiment of the present invention has been described as an aluminum metal strip exiting the casting apparatus and comprising a solid inner layer with altered dendrite structure substantially surrounded by a solid outer layer of the alloy, the form of the product is a sheet, plate, slab. , Wire, rod, bar or other forms.

Although the preferred embodiment of the present invention has been described using a pair of nips to break the dendrites produced when the metal, ie aluminum metal solidifies, the present invention also includes titanium, magnesium, nickel, zinc, tin, copper. It will be apparent to those skilled in the art that they will also be useful for other nonferrous metals.

Claims (31)

A method of continuously casting molten metal into a metal product, Supplying a nonferrous molten metal to a pair of spaced forward advancing casting surfaces; Solidifying the molten metal on the casting surface while advancing the metal between the casting surface to produce a semi-solid inner layer containing metal dendrites between the solid metal outer layer and a solid metal outer layer adjacent the casting surface; Breaking the dendrites of the inner layer; Solidifying the semisolid inner layer to produce a solid metal product consisting of an inner layer and an outer layer; And And recovering the solid metal product from between the casting surfaces. The method of claim 1, wherein the casting surface is the surface of a roll or a belt. The method of claim 1, wherein casting surfaces approach each other and solidifying the semisolid layer is completed at the location of the minimum distance between casting surfaces. 4. The method of claim 3, wherein the casting surface is the surface of a rotating roll having a nip formed therebetween, wherein the completion of the solidification step occurs at the nip. 4. The method of claim 3, wherein the casting surface is the surface of the belt moving over the rotating roll, the roll forming a nip therebetween, and the completion of the solidification step occurs at the nip. 5. The method of claim 4, wherein the product exits the nip at a speed of about 25 to 400 feet per minute. 5. The method of claim 4, wherein the product exits the nip at a speed of at least about 100 feet per minute. 7. The method of claim 6, wherein the force exerted by the rolls on the metal advancing between the rolls is at most about 300 pounds per inch of width of the product. The method of claim 1, wherein the article is a metal strip having a thickness of about 0.06 to about 0.25 inches. The continuous casting method according to claim 1, wherein the metal is an aluminum alloy. A continuous casting method according to claim 1, wherein the metal is a magnesium alloy. The method of claim 1, wherein the metal is a titanium alloy. The method of claim 1, wherein the composition of the solidified inner layer of metal is different from the composition of the outer layer of metal. 2. The method of claim 1, further comprising the step of continuously in-line rolling the recovered solid metal product. 2. The method of claim 1, further comprising off-line rolling the recovered solid metal product in a separate process. The method of claim 1, wherein the metal article comprises an automotive seat article. The method of claim 1, wherein the metal article comprises an aircraft seat article. The method of claim 1, wherein the metal product comprises a beverage can body raw material. The method of claim 1, wherein the metal product comprises a beverage can end raw material or a beverage can tab raw material. In strips of nonferrous alloys, An outer layer of a pair of nonferrous alloys; And And having a spherical dendrite and comprising a central layer of the nonferrous alloy located between the outer layers, the outer layer and the central layer being produced in a strip by continuous casting of molten metal of the nonferrous alloy composition. Characterized in that the strip of nonferrous alloys. 21. The strip of non-ferrous alloy of claim 20, wherein the strip has a thickness of about 0.06 to about 0.25 inches. 22. The strip of non-ferrous alloy according to claim 21, wherein the thickness of the central layer is about 20 to about 30% of the strip thickness. 21. The strip of non-ferrous alloy according to claim 20, wherein the strip is produced by continuously casting molten metal of the non-ferrous alloy composition between a pair of rotating rolls. 22. The strip of non-ferrous alloy according to claim 21, wherein the spherical dendrites are not processed. 21. The strip of non-ferrous alloys of claim 20, wherein the nonferrous alloy is an aluminum alloy. 21. The strip of non-ferrous alloys of claim 20, wherein the nonferrous alloy is a magnesium alloy. 21. The strip of non-ferrous alloys of claim 20, wherein the nonferrous alloy is a titanium alloy. 21. The strip of non-ferrous alloy according to claim 20, wherein the strip comprises an automotive seat product. 21. The strip of non-ferrous alloy as claimed in claim 20, wherein the strip comprises an aircraft seat product. 21. The strip of non-ferrous alloy according to claim 20, wherein the strip comprises a beverage can body raw material. 21. The strip of non-ferrous alloy according to claim 20, wherein the strip comprises a beverage can end raw material or a beverage can tab raw material.