JP2005536354A - Non-ferrous metal casting - Google Patents

Abstract

[PROBLEMS] To cast non-ferrous metal alloy having no segregation in a central region. A non-ferrous alloy molten metal (M) is supplied to a casting apparatus, and at least a part of the non-ferrous alloy is cooled at a rate of 100 ° C. The outer layer (6, 8) of the non-ferrous alloy is solidified to surround the inner layer (16) composed of the molten metal and the solid component of the dendrite (14). The dendrite (14) is processed to form a good anti-crack cast product.

Description

  The present invention relates to casting of non-ferrous metal alloys. In particular, it is a casting of a non-ferrous metal alloy that includes a rapidly solidified shell and broken dendrites, forming a segregation-free central region.

  For continuous casting of a metal such as an aluminum alloy, a two-roll casting machine, a block casting machine, and a belt casting machine are conventionally used. Aluminum alloy two-roll casters have achieved good results despite their relatively low productivity and are used commercially to date. The conventional two-roll casting method includes supplying molten metal to a meshing point of a pair of cooling rolls rotating in opposite directions, and is a combination technique of solidification and deformation, from when the molten metal comes into contact with the roll. Solidification begins. The solidified metal forms a “freeze-front” of the melt within the roll engagement point, and the solid metal travels toward the nip, which is the minimum clearance point between the rolls. The solid metal becomes a solid sheet and passes through the nip. The solid sheet is deformed by a roll (hot roll processing) and exits the roll.

  Aluminum alloys are cast into 1/4 inch thick sheets at a rate of about 4 to 6 feet per minute, that is, roll casting at about 50 to 70 pounds per hour (lb / hr / inch) of cast width. Has been successful. Attempts have been made to increase the speed of roll casting, but they have failed due to central segregation. In roll casting systems, it is recognized that reduced size sheets (eg, less than about 1/4 inch thick) could be produced faster than large size sheets, but about 70 pounds. The possibility of an aluminum roll casting system at a speed exceeding / hour / inch was not clear.

The operation of the two roll casting system with thin dimensions is described in US Pat. No. 5,518,064 (which is incorporated herein by reference) and illustrated in FIGS. The molten metal storage chamber H is connected to an inlet metal T that sends the molten metal M between two water-cooled rolls R ₁ and R ₂ that rotate in opposite directions indicated by arrows A ₁ and A ₂ , respectively. The rolls R ₁ , R ₂ have smooth surfaces U ₁ , U ₂ respectively; any surface roughness of the roll smooth surfaces is effected by manual roll polishing techniques during manufacture. The center line of the rolls R ₁ and R ₂ is in the plane of a vertical or substantially vertical plane L (for example, within about 15 degrees with respect to the vertical), and the cast strip S forms a substantially horizontal position. In another embodiment of the method of the invention, the strip moves vertically upward. The width of the casting strip S is determined by the width of the base T. The plane L passes through the minimum clearance region between the rolls R ₁ and R ₂ , and this point is called a roll nip N. There is a solidification region between the solid casting strip S and the molten metal M, which includes a liquid phase, a solid phase, and a mixing region X. A solidification tip F is formed between the region X and the casting strip S as a complete solidification line.

In the conventional roll casting method of aluminum alloy, the heat of the molten metal M is transmitted to the rolls R ₁ and R _2, and therefore the position of the solidification tip F is maintained upstream of the nip N. In this way, the molten metal M is solidified with a thickness larger than the dimension of the nip N. The solid cast strip S is processed by rolls R ₁ and R ₂ and processed to the final strip thickness. In the conventional roll casting method, a unique property is generated in the strip characteristics of the roll cast aluminum alloy strip by hot rolling the solidified strip between the rolls R ₁ and R ₂ . In particular, the eutectic forming component (eutectic forming material) of alloys such as Fe, Si, Ni, and Zn is abundant in the central region of the strip thickness, and the peritectic forming components (Ti, Cr, V, Zr) are insufficient. To do. The central region is rich in eutectic forming material (ie, alloy components other than Ti, Cr, V, Zr) because that portion of the strip S corresponds to the solidification tip region, and solidification occurs last. This is because it is known as “centerline segregation”. The expansion of center separation in the strip immediately after casting is a factor limiting the speed of conventional roll casting equipment. The strip immediately after casting also shows the trace of processing by the roll. Crystal grains formed during solidification upstream of the nip are flattened by the roll. Therefore, the roll-cast aluminum contains crystal grains that are stretched at an angle in the roll processing direction.

The roll gap of the nip N can be lowered to form a strip S having a thinner dimension. However, the smaller the roll gap, the greater the roll separation force caused by the solid metal between rolls R ₁ and R ₂ . The magnitude of the roll separating force is affected by the position of the solidification tip F with respect to the roll nip N. As the roll gap decreases, the thickness reduction rate of the metal sheet increases and the roll separation force increases. The relative positions of the rolls R ₁ and R ₂ for forming the desired roll gap could not counter the roll separation force at a certain point, and reached the minimum thickness dimension at the position of the solidification tip F.

  The roll separation force can be reduced by increasing the roll speed and moving the solidification tip F downstream toward the nip N. When the solidification tip moves downstream (toward the nip N), the roll gap can be lowered. This movement of the solidification tip F reduces the ratio of the strip thickness at the solidification start point to the roll gap at the nip N. Therefore, proportionally less solidified metal and less roll and hot roll processing, the roll separation force is reduced. In this way, as the position of the solidification tip F moves toward the nip N, proportionally more metal is solidified and hot rolled to a thinner dimension. According to the conventional method, roll casting of a thin strip is performed as follows. First, a relatively thick strip is roll cast and the size is reduced (by increasing the roll speed) until the roll separation force is maximized and the solidification tip is moved forward to reduce the roll separation force. The dimensions are further reduced until the roll separation force is maximized again. The solidification tip is moved forward, the dimension is reduced until the desired thin dimension is reached, and this is repeated. For example, a 10 mm strip S is rolled and the thickness is reduced (eg, 6 mm) until the roll separation force becomes excessive, inevitably increasing the roll speed.

  This method of increasing the roll speed is only feasible until the solidification tip F reaches a predetermined position on the downstream side. In the conventional system, the solidification tip F is set so as not to move forward and enter the roll nip N so that the solid strip is always rolled in the nip N. The nip N is solid to prevent breakage of the cast metal strip S during hot working and to give the delivery strip S sufficient tensile strength to withstand the tensile forces of downstream winders, pinch rolls, etc. Previously, it was necessary to roll the strip. Therefore, in the conventional two-roll casting method in which a solid strip of aluminum alloy is hot-worked at the nip N, the roll separation force is on the order of several tons per inch of width. Although it is possible to reduce the thickness dimension to some extent, it is very difficult to further reduce the strip dimension by operating with such a high roll separation force and ensuring the deformation of the strip at the nip N. I have to. The operating speed of the roll caster is limited by the need to maintain the solidification tip F upstream of the nip N and prevent center separation. Therefore, the roll casting speed of the aluminum alloy was relatively low.

  It has been disclosed in US Pat. No. 6,193,818 that a roll separation force is reduced to some extent to obtain an acceptable microstructure in an aluminum alloy having a high alloy component content. To do. An alloy containing 0.5 to 13 wt% Si is roll cast and is 0.05 to 0.2 inches thick with a roll separation force of about 5000 to 40 at a speed of about 5 to 9 feet per minute. When 0.05 lb / in, strips about 0.05 to 0.2 inches thick are roll cast. Although this approach is an advancement with reduced roll separation forces, these forces still impose significant process improvements. Moreover, productivity remains compromised, and the strip obtained by US Pat. No. 6,193,818 clearly has some degree of center separation and grain stretching as shown in FIG.

The main problem with high speed roll casting is the difficulty in achieving uniform heat transfer from the melt to the smooth surfaces U ₁ , U ₂ , ie, cooling of the melt. In practice, the surfaces U ₁ and U ₂ have various defects that change the heat transfer characteristics of the roll. At high roll speeds, such non-uniformity of heat transfer becomes a problem. For example, in the area of the appropriate surfaces U ₁ and U ₂ , the molten metal M is cooled at a desired position upstream of the nip N, but in an area where the heat transfer characteristics are insufficient, the molten metal is allowed to advance beyond the desired position. Resulting in a non-uniform cast strip.

  Roll casting of thin steel strips has been successful in vertical roll casters at high speeds (up to about 400 feet per minute) and low roll separation forces. The rolls of the vertical caster are arranged side by side, so that the strip is formed in a downward direction. In this vertical orientation, the melt is supplied to the point of engagement between the rolls to form a pool of melt. The upper surface of the molten metal pool is often protected from the ambient atmosphere by an inert gas.

  Although the vertical two-roll casting system from the molten pool has been successful for steel, vertical control of an oxidation sensitive alloy (eg, aluminum) requires further control. The following literature suggests a laboratory-scale solution to this problem of aluminum oxidation in vertical roll casting. Haga et al., “High Speed Roll Casting of Aluminum Alloy” ICAA-6 Preprint “Aluminum Alloy” Vol. 1, 327-332 (1998). According to that method, a stream of molten aluminum alloy is jetted directly from a gas pressurized nozzle into one or both of two rolls of a vertical roll caster. Although high speed casting of aluminum alloy strips has been reported, the main drawback of this method is that the feed rate of the molten aluminum alloy must be carefully controlled to ensure that the cast strip is of uniform thickness. . When a stream is ejected onto the roll, the stream becomes a strip and solidifies. As a stream is jetted onto each roll, each stream is half the thickness of the cast strip. In any case, any slight variations in gas pressure or molten aluminum alloy feed rate will appear as cast strip non-uniformity. In this scheme of aluminum alloy roll casting, parameter control is not practical on a commercial scale.

  Continuous casting of the aluminum alloy achieved a productivity of about 1400 pounds per inch width per inch, about 3/4 inch (19 mm) thick, with a belt caster feeding about 20-25 feet per minute. The conventional belt casting machine described in U.S. Pat. No. 4,0021,977, which is incorporated herein by reference, supplies molten metal to the casting area between a pair of rotating flexible metal belts. Each of the two flexible casting belts rotates in a passage composed of an upstream roller disposed at one end of the casting region and a downstream roller disposed at the other end of the casting region. In this way, the casting belt converges directly around each other around the upstream roller and forms an entrance to the casting area in the nip between the upstream rollers. The molten metal is fed directly to the nip. The molten metal solidifies while being carried between the moving belts. The heat released from the solidified metal is extracted through the two belt sections in contact with the metal being cast. This heat is removed by cooling the opposite surface of the belt with a substantially continuous water film that flows and moves rapidly against the opposite surface of the belt.

  The operating parameters of belt casting are significantly different than those of roll casting. In particular, there is no intentional hot rolling of the strip. Metal solidification is completed approximately 12-15 inches (30-38 cm) away from the nip, resulting in a thickness of 3/4 inch. The belt is exposed to high temperatures when one surface contacts the melt and the inner surface is cooled by water. This causes distortion in the belt. The belt tension must be adjusted to take into account expansion or contraction due to temperature fluctuations in order to obtain a uniform surface condition for the strip. Until now, casting of aluminum alloys with belt casters has been mainly for products with minimal surface condition requirements or products that are subsequently painted.

  The problem of thermal instability of the belt is avoided in the block casting system. In the block casting apparatus, a plurality of cooling blocks are arranged in contact with each other on a pair of opposed passages. The cooling block rotates in the opposite direction to form a casting area during which molten metal is fed. The cooling block acts as a heat sink when the heat of the molten metal is transferred to it. The solidification of the metal is completed approximately 12 to 15 inches downstream from the entrance of the casting area, resulting in a thickness of 3/4 inch. The heat transferred to the cooling block is removed during the return loop. Unlike the belt, the cooling block is not distorted by the heat transferred. However, block casting requires strict dimensional control to prevent non-uniformity and gaps between blocks that cause defects in the casting strip.

  The idea of transferring the heat of the melt to the casting surface has been adopted in belt casting machines that have been modified to some extent, as described in US Pat. Nos. 5,515,908 and 5,564,491. These patents are incorporated herein by reference. In the heat sink type belt casting machine, the molten metal is supplied upstream of the nip of the belt (casting surface), solidification starts before reaching the nip, and heat transfer continues until reaching the downstream nip. In this method, since the molten metal is supplied to the belt along the curved surface of the upstream roller, the metal is almost solidified before reaching the nip between the upstream rollers. The heat of the melt and cast strip is transferred to the belt in the casting area (including the downstream nip). Heat is then removed from the belt when it is not in contact with either the melt or the cast strip. In this way, the belt portion of the casting area (which is in contact with the melt and the casting strip) is not subject to the large temperature fluctuations that occur in conventional belt casting machines. The thickness of the strip is constrained by the heat capacity of the belt between which casting is taking place. Production of strips from 0.08 to 0.1 inches (2 to 2.5 mm) was achieved at a production rate of 2400 pounds / hour / inch.

  Problems associated with belts used in conventional belt casting remain. In particular, cast strip uniformity is affected by belt stability (ie, tension). In any belt casting machine, a normal or heat sink type object causes instability of the belt when there is heat transfer from the metal solidified by contact of the high-temperature molten metal to the belt. Furthermore, the belts need to be changed regularly, which reduces productivity.

  Non-ferrous alloy strip materials are desired for use as sheet products in the automotive and aerospace industries and for the manufacture of can bodies. Conventional can body stock is manufactured in a batch system, and many individual processes are arranged. If ingots are needed for further processing, first scale, heat treat to homogenize alloy, cool, roll multiple times while still hot, hot finish roll processing, final Winding, air cooling and storage are performed. The coil is annealed in a batch mode. The wound sheet stock is finished to final dimensions by an unwinder, winder, single or tandem roll mill. Batch processes typically used in the aluminum industry require handling of many different materials and move ingots and coils between individual processing steps.

  Direct cooling casting for continuous production of can body stock is described in U.S. Pat. No. 4,260,419, which describes a small scale machine for continuous strip casting. Both systems require many material handling operations to move the ingot and coil. Such an operation is labor intensive and consumes energy and often damages the product.

  US Pat. Nos. 5,772,802 and 5,772,799, which are incorporated herein by reference, disclose a belt casting method that includes a can or lid stock and a method of manufacturing the same, including an alloy. A low content aluminum alloy is strip cast to form a hot strip cast feedstock, which is immediately quenched and annealed to prevent substantial precipitation and the alloy components are It is quenched immediately and cold rolled to prevent substantial precipitation. This method has been successful today despite the relatively low production rates achieved.

  Furthermore, alloys other than aluminum, such as magnesium alloys, are not continuously cast on a commercial scale. Magnesium metal has a hexagonal crystal structure and severely restricts the amount of strain when added, especially at low temperatures. Forged magnesium alloy products are therefore usually carried out by hot working in the range of 300 to 500 ° C. Even under such conditions, multiple roll passes and intermediate annealing are necessary. In the conventional ingot method, a total of 25 roll passes and intermediate annealing are performed, and the final product is used for manufacturing a thickness of 0.5 mm. As a result, forged magnesium products tend to be expensive.

  Therefore, a need continues to exist for an economical casting method for non-ferrous alloys that achieves a uniform casting surface.

  This need has been solved by the method of the present invention for casting non-ferrous metals. It supplies a non-ferrous metal melt to a pair of spaced apart casting surfaces and rapidly cools at least a portion of the non-ferrous metal at a rate of at least about 100 ° C. per minute, thereby solidifying the outer layer of the non-ferrous alloy. Enclose the inner layer of the molten component and the solidified component of the dendrites. Suitable alloys include aluminum alloys, magnesium alloys and titanium alloys. As the alloy is cast, the solidified outer layer increases in thickness. As the inner layer solidifies, the dendrite in the inner layer is changed to a smaller structure, such as by breaking the dendrite or by separation. The product exiting the casting apparatus encloses a solidified inner layer containing altered dendrites (substantially avoiding or minimal central separation) surrounded by a solidified outer layer of alloy. Depending on the type of casting equipment, the product is in the form of sheets, plates, slabs, foils, wires, rods, bars and other extruded structures. Suitable end products include automotive seat products, space seat products, beverage can body stock, beverage can end plates and tab stock.

  The casting surface can be a roll surface of a roll caster, a belt surface of a belt caster, or other conventional remote casting surfaces that are close to each other. The process of solidifying the semi-solidified layer is completed at the position of the minimum distance between the casting surfaces. In one embodiment, the casting surface is a rotating roll surface that forms a nip therebetween and completes with a solidification process at the nip. For metal traveling between rolls, the force exerted by the roll is a maximum of about 300 pounds per inch of product width. In another embodiment, the casting surface is a belt surface that moves over a rotating roller, the rolls forming a nip therebetween, and the completion of the solidification process occurs at the nip. The solidified product including the inner layer is delivered at a minimum spacing of the casting surface at a speed of about 25-400 feet per minute, or at a speed of at least about 100 feet per minute.

  The present invention includes products made by the method of the present invention. The product is in the form of a metal strip about 0.06 to about 0.25 inches thick. The thickness of the inner layer accounts for about 20 to about 30% of the strip thickness. One result of the process of the present invention is that the components of the solidified inner layer of the metal are different from the components of the outer layer of the metal. Furthermore, the dendrite with broken inner layer metal is in the shape of a sphere (raw).

  Throughout the following description, a complete understanding of the present invention can be obtained by reference to the accompanying drawings in which like reference characters refer to like parts throughout.

  The following is for purposes of illustration and should be understood to assume various other changes and processes unless specifically stated otherwise. It should be understood that the predetermined apparatus and steps shown in the accompanying drawings, and the description of the specification are merely exemplary embodiments of the invention. Accordingly, the specific dimensions and other physical characteristics described herein are not to be understood as limiting the invention. If any numerical range is stated, it should be understood that the range includes all numerical values and fractional parts between the minimum and maximum stated therein.

  The present invention includes a method for casting a non-ferrous alloy, which includes feeding the non-ferrous alloy to a casting apparatus. A non-ferrous alloy means an alloy component such as aluminum, magnesium, titanium, copper, nickel, zinc, or tin. Particularly suitable non-ferrous alloys for use in the present invention are aluminum alloys, magnesium alloys and titanium alloys.

  The terms “aluminum alloy”, “magnesium alloy”, “titanium alloy” mean an alloy containing at least 50% by weight of the indicated ingredients and at least one modifier component. Aluminum, magnesium and titanium alloys are attractive candidates for structural materials in the aerospace and automotive industries. This is because they are lightweight, have a high ratio per weight, and a high specific stiffness at both room temperature and high temperature. Suitable aluminum alloys include the aluminum association 3xxx and 5xxx series alloys. Examples of magnesium-based alloys include Mg-Al series, Mg-Al-Zn series, Mg-Al-Si series, Mg-Al-rare earth (RE) series, Mg-Th-Zr series, Mg-Th- There are Zn—Zr series, Mg—Zn—Zr series, and Mg—Zn—Zr—RE series.

  The most basic form of the invention is illustrated in the flow chart of FIG. In step (100), molten non-ferrous metal is supplied to the casting apparatus. The casting apparatus includes a pair of remotely advancing casting surfaces as described below. In step (102), the casting apparatus quickly cools at least a portion of the non-ferrous alloy, and the outer layer of the non-ferrous alloy is solidified while the inner layer remains in a semi-solid state. The inner layer includes a molten metal component and a metal dendrite solidification component. As the alloy is cast, the solidified outer layer increases in thickness. The dendrite of the inner layer is changed by breaking the dendrite in step (104) to form a smaller structure. In step (106), the inner layer is solidified. The product present in the casting apparatus includes a solidified inner layer that includes sandwiched dendrites in the outer layer of the alloy. The product may be in various forms, including but not limited to sheets, plates, slabs, and foils. Extruded cast products are in the form of wires, rods, bars, or other extruded products. In another example, the product is further processed and processed in step (108). The order of steps (100)-(108) is not fixed in the method of the present invention and may occur in sequence or several steps may occur simultaneously.

  The present invention balances the solidification of the molten metal, the formation of dendrites in the solidified metal, and the rate of change of the dendrites, thereby obtaining desired properties in the final product. The cooling rate is selected so that rapid solidification of the outer layer metal is completed. For aluminum alloys and other non-ferrous alloys, cooling of the outer metal layer occurs at a rate of at least about 100 ° C. per minute. For example, a suitable casting apparatus, such as a two-roll caster, a belt caster, a slab caster, or a block caster, has a cooled casting surface. Vertical roll casters are also used in the present invention. In continuous casters, the casting surfaces are usually remote and there are areas where the spacing between rolls is minimal. In roll casters, the area of minimum spacing between casting surfaces is the nip. In a belt caster, the area of minimum spacing between the casting surfaces of the belt is the nip between the caster's entry side pulleys. As will be described in more detail below, the operation of a casting apparatus of the type of the present invention involves the solidification of the metal at the minimum spacing of the casting apparatus. In the following, the method of the invention carried out using a two-roll caster is described, but this is not meant to be limiting. Other continuous cast surfaces can be used to practice the present invention.

By way of example, a roll caster (FIG. 1) can be used to implement the present invention, as shown in detail in FIG. In FIG. 1 (this is generally horizontal continuous casting in the conventional example and the present invention), the present invention uses a pair of cooling rollers R ₁ and R ₂ that rotate in opposite directions in the directions of arrows A ₁ and A _2. Is called. The term horizontal as used herein means that the casting strip is in a horizontal orientation or an angle of about plus or minus about 30 degrees from the horizontal. As described in more detail in FIG. 3, the supply mouthpiece T is formed of a heat-resistant or other ceramic materials, the roll R ₁ which is rotating in the reverse direction indicated by the arrow A _1, A ₂ from one another, R ₂ The molten metal M is supplied directly in the direction of arrow B upward. The gaps G ₁ and G ₂ between the supply base T and the respective rolls R ₁ and R ₂ are kept as small as possible to prevent the molten metal from leaking out, and the molten metal follows the rolls R ₁ and R ₂ . Minimize exposure to the open air. While avoiding the contact between the cap T and the roll R _1, R _2, suitable dimensions of the gap G1, G2 is about 0.01 inches (0.25 millimeters). Plane through the center line of the roll R _1, R ₂ passes through the region of minimum spacing of the rolls R _1, R _2, it is a roll nip N.

Molten metal M is supplied to the casting surface of the roll casting machine which is the cooled rolls R ₁ and R ₂ . The molten metal M contacts in the regions (2) and (4) of the rolls R ₁ and R ₂ , respectively. When it comes into contact with the rolls R ₁ and R ₂ , the molten metal M cools and starts to solidify. Cold metal, the upper shell (6) and adjacent to the roll R _1, a lower shell (8) adjacent to the roll R _2. The thickness of the lower shell (8) and the upper shell (6) of the solidified metal increases as the metal advances toward the nip N. A solid metal large dendrite (10) (not actual dimensions) is formed at the contact between the upper and lower shells (6), (8) and the molten metal M. The large dendrite (10) is broken and drawn into the slower moving central part of the molten metal M. Then, it conveyed in the direction of the arrow C _1, C _2. The flow pulling action breaks the large dendrites (10) into smaller dendrites (14) (not actual dimensions). In the central portion (12), the upstream of the nip N is a region (16), and the metal M is in a semi-solid state and contains a solid component (solidified small dendrite (14)) and a molten metal component. The metal M in the range (16) has a bowl-like viscosity, partly because small dendrites (14) are dispersed therein. At the position of the nip N, the portion with the molten metal is squeezed back in the direction opposite to the arrows C ₁ and C ₂ . Rolls R ₁ and R ₂ rotate forward in the nip, so that only substantially solid parts of the metal (small dendrite (14) in upper and lower shells (6), (8) and central part (12)) The molten metal in the central portion (12) is pushed back upstream from the nip N so that the metal solidifies completely past the point at the nip N. Downstream of the nip N, the central portion (12) is a central solid layer comprising a small dendrite (14) sandwiched between an upper shell (6) and a lower shell (8). In the central layer (18), the small dendrite (14) is about 20 to about 50 microns in size and is generally spherical. In strip products, the solid central portion is about 20 to about 30% of the total thickness of the strip. The casting apparatus of FIG. 4 shows a situation in which the strip S is manufactured in a substantially horizontal direction, but the strip S may go out obliquely or vertically, and is not limited.

The casting process described for FIG. 4 follows the method steps described above. In step (100), the molten metal supplied to the roll casting machine starts cooling and solidifies in step (102). Metal that is being cooled is to expand the outer layer of cooling the casting surface (R _1, R ₂₎ near or adjacent to solidified metal (6) (8). The thickness of the solidified layer (6) (8) increases as the metal progresses through the casting apparatus. With respect to step (102), dendrites (10) are formed in the metal of the inner layer (12) that is at least partially surrounded by the solidified outer layers (6), (8). In FIG. 4, the outer layer (6) (8) almost surrounds the inner layer (12), like a sandwich with an inner layer (12) between two outer layers (6) (8). In other casting devices, the outer layer completely surrounds the inner layer. In step (104), the dendrite (10) is changed. That is, it is broken into smaller structures (14). In the inner layer (12), before the metal is completely solidified, the metal is a semi-solid containing a solid component (solidified small dendrite (14)) and a molten metal component. The metal at this stage is tender and soft due to the partial dispersion of small dendrites (14) therein. In the process (106) at the position where the metal is completely solidified in the casting apparatus, the solidified product has an inner part (18) comprising a small dendrite (14) at least partially surrounded by the outer part. . The internal thickness is about 20 to about 30% of the product thickness. In the inner part, the small dendrites are of a size of about 20 to about 50 microns and have little processing of the casting equipment and are therefore usually spherical.

  In the present invention, the molten metal in the inner layer (12) (as described for casting between rolls) is squeezed in the opposite direction to the flow direction in the casting apparatus and / or pushed into the outer layers (6) (8). And reach the outer surface of the outer layer (6) (8). The operation of squeezing and / or forcing the molten metal in the inner layer occurs in any casting apparatus described herein.

  In step (104), dendrite breakage in the inner layer occurs during casting between rolls due to shear forces resulting from the velocity difference between the inner and outer layers of molten metal. Operating a roll caster at a conventional speed of less than 10 feet per minute does not generate the shear force required to break such dendrites. As described above, when the conventional roll casting machine is operated at a high speed (more than 25 feet per minute) while controlling solidification, the casting specified in the present invention can be performed. May be operated in a manner to achieve An important feature of the present invention is the breaking of dendrites in the inner layer. Dendritic breakage minimizes or avoids center separation, thereby improving the formability and elongation properties of the final product. This is because conventional roll casting or belt casting products show cast segregation and contain coarse components, but in the present invention such coarse components are reduced or absent. Other suitable mechanisms for breaking the dendrites in the inner layer include mechanical stirring (e.g., propeller) in the liquid, electrical stirring including rotary stator stirring, linear stator stirring, and high frequency supersonic vibration.

  The casting surface acts as a heat sink against the heat of the melt. In the present invention, heat is transferred from the molten metal to the cooled casting surface in a uniform manner, ensuring uniform surface of the cast product. The casting surface is made of steel or copper and is textured to provide a non-uniform surface for contact with the molten metal. Surface non-uniformity helps to increase heat transfer from the chilled casting surface. By providing a predetermined degree of non-uniformity in the surface of the cooling cast surface, heat transfer from that surface can be made uniform. The surface non-uniformity can be in the form of grooves, dimples, bumps, or other structures, spaced apart from each other in a regular pattern, with a surface non-uniformity of about 20 to about 120 per inch. Or a regular pattern with a non-uniformity of about 60 per inch. The surface non-uniformity is about 5 to about 50 microns in height, or about 30 microns in height. The cold cast surface is coated with a chrome or nickel material to facilitate separation of the cast product therefrom.

  The casting surface is usually heated during casting and is susceptible to oxidation at high temperatures. If oxidation of the casting surface occurs unevenly during casting, the heat transfer characteristics there may change. Thus, the casting surface is pre-oxidized prior to use, minimizing changes therein during casting. Brushing the casting surface from time to time or continuously is desirable to remove contaminants that accumulate during the casting of non-ferrous alloys. Small pieces of the cast product break and leave the product and adhere to the casting surface. These small pieces of non-ferrous alloy products tend to oxidize, making the heat transfer characteristics of the casting surface non-uniform. Brushing the casting surface avoids non-uniformity problems caused by the accumulation of contaminants on the casting surface.

In the roll casting machine operated by the method of the present invention, the control / maintenance / selection of an appropriate speed of the rolls R ₁ and R ₂ affects the operability of the present invention. The roll speed determines the speed at which the molten metal M advances to the nip N. If the speed is too slow, the large dendrite (10) will be drawn into the center (12) and will not receive sufficient force and will not break into a small dendrite. Thus, the present invention is suitable to operate at high speeds of, for example, about 25 to about 400 feet per minute, or about 100 to about 400 feet per minute, or about 150 to about 300 feet per minute. Linear rate per unit area of the molten aluminum is supplied to the roll R _1, R ₂ a roll R _1, lower than the speed of R _2, or would be about a quarter of the roll speed. High speed continuous casting according to the present invention may be achieved in part because the textured surfaces D ₁ , D ₂ ensure heat transfer from the melt M.

The roll separation force is an important parameter for carrying out the present invention. The main advantage of the present invention is that the solid strip does not form until the metal reaches the nip N. The thickness is determined by the size of the nip N between the rolls R ₁ and R ₂ . The roll separation force is large enough to squeeze the molten metal away from the nip N and send it upstream. If the molten metal passing through the nip N is excessive, the upper and lower shells (6), (8) and the solid central portion (18) are separated from each other and do not align straight. If the molten metal reaching the nip N is insufficient, a strip that is too early in time, as occurs in the conventional roll casting process, is formed. The strip 20 that is too early in time is deformed by the rolls R ₁ and R ₂ to cause center separation. A suitable roll separation force is about 25 to about 300 pounds per inch of casting width, or about 100 pounds per inch of casting width. When casting a thick non-ferrous alloy, the casting speed needs to be slower to remove heat from the thick alloy. Unlike conventional roll casting, a fully solidified non-ferrous strip is not formed upstream of the nip, and the present invention does not generate excessive roll separation force even at such a low casting speed.

  Non-ferrous alloy strips having a thickness of about 0.1 inch or less (eg, 0.06 inch) will be produced at a casting rate of about 25 to about 400 feet per minute. Larger non-ferrous alloy strips can also be produced by the method of the present invention. For example, it is about 0.25 inches thick. Casting at the linear speed planned in the present invention (eg, about 25 to about 400 feet per minute) solidifies the non-ferrous alloy product about 1000 times faster than the non-ferrous alloy in the ingot state, and the non-ferrous alloy of the ingot Improve product characteristics over casting.

  The present invention further includes a non-ferrous alloy product cast according to the present invention. The non-ferrous alloy product includes an inner portion that is substantially surrounded by an outer portion. The alloy component concentration is different inside and outside. The molten alloy has an initial concentration of alloy components including a peritectic forming alloy component and a eutectic forming alloy component. The concentration of the alloy component is different between outside and inside. Compared to the concentration of eutectic forming material and peritectic forming material in each metal and the outer part, a predetermined component (for example, eutectic forming material) is drastically reduced inside the product and other components (for example, peritectic forming material). Will be abundant. The crystal grains of the non-ferrous alloy product of the present invention are not substantially deformed. That is, it has an equiaxed structure like a sphere. Since there are no hard particles inside the product, the central separation and cracking typically encountered in the casting of many non-ferrous alloys is minimized or avoided.

In practicing the present invention, it is desirable to support the product that has exited the casting apparatus and to be sufficiently cooled and self-supporting. An example of the support mechanism shown in FIG. 5 is one in which a continuous conveyor belt B is disposed below the strip S exiting the rolls R ₁ and R ₂ . Belt B transitions around pulley P and supports strip S at 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 used for belt B include those that use fiberglass and metal (eg, steel) in rigid form or in mesh form. Alternatively, as shown in FIG. 6, there is a support mechanism including a fixed support surface J such as a metal shoe, on which the strip S moves while cooling. The shoe J is made of a material to which the hot strip S does not easily adhere. If the strip breaks as soon as it exits rolls R ₁ and R ₂ , the strip S is cooled at location E by a fluid such as air or water. For aluminum alloys, the strips exiting rolls R ₁ and R ₂ are typically about 1100 ° F., which reduces the temperature of the aluminum alloy strip to about 1000 ° F. about 8 to 10 inches inside from nip N Is desirable. One suitable cooling mechanism that has cooled the strip at position E and achieved the above cooling is described in US Pat. No. 4,823,860, which is incorporated herein by reference.

<Example>
Aluminum alloys containing 0.75Si, 0.20Fe, 0.80Cu, 0.25Mn, 2.0Mg by weight were cast according to the present invention. And it was made into the dimension of 0.015 inch by the roll process in a line hot and cold. The characteristics of the two types of products are shown in Table 1. Example 1 shows the characteristics obtained immediately after roll cooling after winding and cooling. The combination of high strength and ease of processing (elongation) is noted. The combination of high tensile strength and elongation achieved in Examples 1 and 2 has not previously been achieved with the 5xxx series of aluminum-manganese alloys. For comparison, the aluminum alloy 5182 has a tensile strength of 54 ksi and an elongation of 7% at best. Example 2 shows the properties obtained by solution heat treating the sheet and normalizing to 275 ° F. in the laboratory. Good tensile strength and excellent bending properties were achieved.

  By carrying out the method of the present invention, the non-ferrous cast alloy product has improved tensile strength and elongation compared to conventional cast products. Such improved properties allow for the production of thinner products, which is desirable in the market.

  Products exiting the casting apparatus are subsequently formed into other forms, for example by roll processing, or else can sheet materials, tab stock, automotive sheet materials and other final products including plate making and glossy sheets Processed to produce the product. Subsequent processing of the product exiting the casting apparatus is done by a line rolling apparatus and utilizes the heat of the sheet immediately after casting (related to the following US patents, which are incorporated herein by reference). 5772799, 5778022, 5356495, 5496423, 5514228, 5470405, 6343496, 6280543). Alternatively, the sheet just after casting is cooled and then rolled off-line. Other processing of the sheet can be performed using one or more of the above patents.

  Although the preferred embodiments of the present invention have been described above for the automotive and aerospace industries and the soft drink can industries, which are particularly effective, those skilled in the art will be able to use the present invention for manufacturing the following parts. It will be clear. Boat, canoe, ski, piano, harp, delivery truck body, truck cabs, garbage collection storage tank, raceboat cover, civilian airplane parts, fire truck hose hangar, material handling equipment, dock boards, Radar tracking systems, electronic equipment cabinets, vibratory screens, tote bins, trunk frames and side plates, ladders, water heating anodes, including portable lamps, space equipment components, rockets and satellites , Typewriters, rocket launchers and mortar bases, loom parts, concrete buckets and hand finishing tools, jigs and fixtures and vibration testing machines.

  Although the embodiments of the present invention have been described for horizontal casting of a particularly effective non-ferrous alloy, those skilled in the art will recognize that the present invention also applies to vertical casting as well as casting at any angle between vertical and horizontal casting. It will be clear that it is useful.

  A preferred embodiment of the present invention has been described above for an aluminum metal strip product exiting a casting apparatus, the casting apparatus comprising a modified dendrite structure and comprising a solid inner layer substantially surrounded by a solid outer layer of alloy. Including, the product is in the form of a sheet, plate, slab, foil, wire, rod, bar or extrusion.

  While the preferred embodiment of the present invention has been described above using a two-roll nip to break the dendrite formed when the metal solidifies, it is aluminum metal and those skilled in the art will recognize that the present invention is titanium. It will be apparent that other non-ferrous metals are also useful, including magnesium, nickel, zinc, tin and copper.

Partial schematic diagram of a casting machine with a molten metal supply base and a pair of rolls FIG. 2 is an enlarged sectional view of a molten metal supply base and a roll shown in FIG. Flow chart of casting process in the present invention Explanatory drawing of melt casting operating according to the present invention Schematic view of a casting machine made in accordance with the present invention with a strip support mechanism and optional cooling means Schematic view of a casting machine made in accordance with the present invention with other strip support mechanisms and optional cooling means

Explanation of symbols

M molten metal R ₁ , R ₂ roll T molten metal supply base S solidified cast strip N nip
6,8 outer layer
18 Inner layer
10 Large dendrite
14 Broken dendrite

Claims (31)

Supplying a non-ferrous metal melt to a pair of casting surfaces approaching from a distance;
A step of solidifying the molten metal on the casting surface while advancing the metal between the casting surfaces, forming a solid metal outer layer in contact with the casting surface, and a semi-solid inner layer including metal dendri between the solid metals;
Breaking the dendrite in the inner layer;
Solidifying the semi-solid inner layer to form a solid metal product having an inner layer and an outer layer;
Drawing solid metal products from between casting surfaces,
A method of forming a metal product by continuously casting a molten metal. The method of claim 1, wherein the casting surface is a roll or belt surface. The method of claim 1, wherein the casting surfaces are close together and the step of solidifying the semi-solid inner layer is completed at a location where the distance between the casting surfaces is minimal. The method of claim 3, wherein the casting surface is the surface of a rotating roll having a nip therebetween, and the step of completing solidification occurs at the nip. 4. The method of claim 3, wherein the casting surface is the surface of a belt that transitions over a rotating roll, the rolls forming a nip therebetween, and completion of the solidification process occurs at the nip. The method of claim 4, wherein the product exits the nip at a speed of about 25 to about 400 feet per minute. The method of claim 4, wherein the product exits the nip at a speed of at least about 100 feet per minute. The method of claim 6, wherein the force applied by the rolls to the metal traveling between the rolls is up to about 300 pounds per inch of product width. The method of claim 1, wherein the product is a metal strip having a thickness of about 0.06 to about 0.25 inches. The method of claim 1, wherein the metal is an aluminum alloy. The method of 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 solidified inner layer metal component is different from the outer layer metal component. The method of claim 1, further comprising rolling the drawn solid metal product in a line. The method of claim 1, further comprising rolling the drawn solid metal product off-line. The method of claim 1, wherein the metal product comprises an automotive sheet product. The method of claim 1, wherein the metal product comprises an aerospace product. The method of claim 1, wherein the metal product comprises a soft drink can body stock. The method of claim 1, wherein the metal product comprises a stock of soft drink can end plates or soft drink can tabs. A pair of outer layers of a non-ferrous alloy and a central layer located between the outer layers and including a spherical dendrite, the outer layer and the central layer being formed into a strip by continuous casting of the molten non-ferrous alloy component , Non-ferrous alloy strip. 21. The strip of claim 20, wherein the thickness of the strip is from about 0.06 to about 0.25 inches. 21. The strip of claim 20, wherein the thickness of the central layer is about 20 to about 30% of the thickness of the strip. 21. The strip of claim 20, wherein the strip is manufactured by feeding the molten non-ferrous component between a pair of rotating rolls. The strip of claim 21, wherein the spherical dendrite is green. 21. The strip of claim 20, wherein the non-ferrous alloy is an aluminum alloy. 21. The strip of claim 20, wherein the non-ferrous alloy is a magnesium alloy. 21. The strip of claim 20, wherein the non-ferrous alloy is a titanium alloy. 21. The strip of claim 20, wherein the strip comprises an automotive seat product. 21. A strip according to claim 20, wherein the strip comprises an aerospace product. 21. The strip of claim 20, wherein the strip includes a soft drink can body stock. 21. The method of claim 20, wherein the strip comprises stock of soft drink can end plates or soft drink can tabs.

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