Method and installation for cooling on a reversing hot rolling mill

Abstract

The invention relates to a method for hot-rolling an aluminium alloy of the AA6xxx type by means of a reversing hot-rolling mill equipped with a cooling system.SOLUTION: A first hot-rolling step for processing the rolled plate into a blank based on a first temperature at the start of the hot-rolling, a cooling step at an average cooling rate from the average temperature of the blank obtained down to a second temperature at the start of the second hot-rolling, under deformation and temperature conditions such that the strip recrystallizes to at least 50%; AA6xxx, A rolling process is provided comprising a second hot rolling step for working the thus cooled blank into a strip of final hot rolled thickness and a cold rolling step from the strip into a sheet.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to the field of rolling flat products made of aluminum alloys, more precisely to a reversing hot rolling mill with a very fast, homogeneous and reproducible cooling system for flat products made of aluminum alloys.

[0002] The invention also relates to a method carried out by said reversing hot rolling mill equipped with a cooling system allowing better thermal control of the flat product made of an aluminium alloy during rolling. The invention also relates to a sheet obtained by the method using cooling during hot rolling according to the invention. [Background technology]

[0003] Hot lines for rolling aluminum alloys always include a reversing mill (i.e., a mill that rolls by reciprocating motion), also called a roughing mill or roughing mill, and sometimes a multi-high mill, also called a tandem mill, where the hot metal is coiled at the exit. The number of passes and the pass configuration (thickness reduction per pass) depend on the hardness of the product (its flow stress) and, of course, the output of the rolling mill in terms of torque and stress. Productivity requires the greatest possible reduction in each pass. However, this is limited by the rolling mill's capacity in terms of rolling stress and / or rolling torque, as described, for example, in the paper "Mise en forme de l'aluminium-Laminage-Patrick Deneuville, © Techniques de l'Ingenieur-2010." During hot working of aluminum, such as hot rolling, the temperature of the metal is always typically at least 200°C.

[0004] Furthermore, hot lines are known which have two reversing mills in succession followed by a tandem mill.

[0005] Reversing hot rolling mills are often a bottleneck in in-plant production, and in view of the large investments they represent, increasing their productivity is a major challenge, and obviously the idea has always been to increase the mill's capacity in terms of rolling stresses and / or torques.

[0006] In the prior art, the focus has often been on improving the productivity of tandem rolling mills rather than the productivity of reversing mills. The following applications relate specifically to cooling processes or methods installed on finishing hot tandem rolling mills:

[0007] WO 2015 / 58902 relates to a hot rolling train for aluminum strip and a method for hot rolling aluminum strip.

[0008] The present application aims to propose a solution that allows better adjustment of the temperature-time path and the cooling curve in the product to be rolled during hot rolling of aluminum strip, for a hot rolling train of aluminum strip comprising a multi-stage tandem finishing rolling train with at least one coiler installed downstream in the rolling direction and at least one associated cooling section, wherein one or more cooling sections are arranged in the outlet region of the hot rolling train of aluminum strip, and at least one guillotine installed downstream in the rolling direction is associated with the tandem finishing rolling train.

[0009] EP 2991783 relates to a method for producing a metal strip, in which the strip is rolled in a multi-stage rolling mill, exits the rolling mill in the transport direction behind the last stage, and is cooled in a cooling device. To achieve a favorable fine-grained structure and high flatness, the patent states that the strip or plate is subjected to additional high-speed cooling immediately after passing through the work rolls of the last stage of the rolling mill, whereby the strip or plate is further cooled at least partially in the region of the last stage of the rolling mill in the transport direction by applying a cooling fluid to the strip or plate from above and below, the volumetric flow rate of the cooling fluid applied to the strip or plate from below being at least 120% of the volumetric flow rate of the cooling fluid applied to the strip or plate from above.

[0010] WO 2008 / 89827 relates to an apparatus for cooling a metal strip. The application relates to an apparatus for cooling a metal strip between two stages of a rolling mill, in which the strip is guided over an upper guide element of planar design. A spray element is arranged below the upper guide element, which guides a cooling fluid through at least one opening in the upper guide element toward the underside of the strip. To achieve an improved spray design, the application provides at least two openings arranged side by side transversely to the strip's forward advancement direction and having an elongated shape. The longitudinal axes of the openings are oriented along a fixed angle relative to the strip's forward advancement direction.

[0011] Similarly, methods and equipment exist for cooling the plate prior to the start of hot rolling feed.

[0012] WO 2016 / 012691 relates to a cooling method and installation. The application is directed to a method for cooling a rolled aluminum alloy plate after a metallurgical homogenization heat treatment of said plate and before its hot rolling, characterized in that cooling to a value between 30 and 150°C is carried out at a rate of 150 to 500°C / h, with a homogeneity of less than 40°C over the entire treated portion of the plate. The application is also directed to a facility enabling the implementation of said method as well as said implementation.

[0013] WO 2018 / 011245 is directed to a method for producing a 6xxx series aluminum alloy sheet, comprising the steps of casting a 6xxx series aluminum alloy to form an ingot, homogenizing the ingot, cooling the homogenized ingot directly to the starting temperature of hot rolling at a cooling rate of at least 150°C / h, hot rolling the ingot to a final thickness and coiling it at the final thickness after hot rolling under conditions that allow obtaining a recrystallization rate of at least 50%, and cold rolling to obtain a cold-rolled sheet. The method of the invention is extremely useful for producing sheet for the automotive industry, combining a high tensile elastic limit and formability adapted to cold pressing operations, as well as excellent surface quality and high corrosion resistance, with high productivity.

[0014] For the 6000 series alloys, other modifications to improve manufacturability and / or metallurgical properties are also contemplated.

[0015] EP 1 165 851 relates to a method by which an ingot of a 6000 series aluminum alloy can be converted into a self-annealing sheet. The method comprises subjecting the ingot to a two-stage homogenization treatment, first at a temperature of at least 560°C and then at a temperature of 450°C to 480°C. The method then comprises hot rolling the homogenized ingot at a starting temperature of 450°C to 480°C and then at a destination temperature of 320°C to 360°C. This results in a hot-rolled sheet having an exceptionally low cubic recrystallization content.

[0016] US Patent Application Publication No. 2016 / 0201158 relates to a novel method for increasing productivity on a continuous annealing and re-solution heat treatment line for heat-treating-compatible aluminum sheet products for the automotive industry, which have high strength and low roping after T4 and firing. As a non-limiting example, the method can be used in the automotive industry. The alloys are suitable for heat treatment, and the method can also be applied in the marine, aerospace, and transportation industries.

[0017] EP 1375691 relates to a laminated sheet made of a 6000 series aluminum alloy containing Si and Mg as major components and having excellent formability sufficient to allow flat hemming, excellent bulge resistance, and good hardenability during baking of the coating. The alloy sheet has anisotropy with a Lankford coefficient greater than 0.4 or a resistance coefficient for textured cubic orientation of 20 or greater, a critical radius of curvature of 0.5 mm or less at 180°C, and deflects upon aging at ambient temperature even when the strength to conventional flow threshold is greater than 140 MPa. The invention also relates to a method for producing laminated sheets made of an aluminum alloy, which comprises subjecting an ingot to a homogenization treatment, cooling it to a temperature below 350°C at a cooling rate of at least 100°C / h, optionally down to ambient temperature, heating it again to a temperature of 300-500°C and subjecting it to hot rolling, carrying out cold rolling of the hot-rolled product, and subjecting the cold-rolled sheet to a solution treatment at a temperature of at least 400°C before quenching.

[0018] EP 0786535 relates to the homogenization of an aluminum alloy ingot containing 0.4 to less than 1.7% by weight of Si, 0.2 to less than 1.2% by weight of Mg, and Al, as well as unavoidable impurities in the form of a solid, at a temperature of 500°C or higher. The resulting product is then cooled from 500°C or higher to a temperature in the range of 350 to 450°C, starting from which hot rolling is possible. The hot rolling step is carried out at a temperature in the range of 200 to 300°C, and the cold-rolled product is subjected to a reduction of 50% or higher immediately before a solution treatment. The cold-rolled product is then subjected to a solution treatment, in which the product is stored for at most 10 minutes at a temperature in the range of 500 to 580°C with a temperature increase rate of 2°C / s or higher. The resulting product is then subjected to hardening, during which the product is cooled to a temperature of 100°C or lower with a cooling rate of 5°C / s or higher. Thus, a method for producing an aluminum alloy plate for forming, which has high strength and formability and an excellent appearance on its surface after forming, is obtained, and the plate is suitably used as a material for transportation equipment parts such as exterior plates for automobiles.

[0019] JP 2015-067857 A relates to an Al-Mg-Si based aluminum alloy sheet for automobile panels, which has flat bending processability, is bendable, has excellent press processability, and is excellent in shape stability, paint baking hardenability, and corrosion resistance, and to a manufacturing method for this purpose using an Al-Mg-Si based aluminum alloy sheet for automobile panels, which contains 0.4 to 1.5% Si, 0.2 to 1.2% Mg, 0.001 to 1.0% Cu, 0.5% or less Zn, 0.1% or less Ti, 50 ppm or less B, 0.30% or less of one or more types of Mn, 0.20% or less Cr, and 0.15% or less Zr, with the remainder being Al with unavoidable impurities. The distribution of the Cube orientation density at a depth of one-quarter of the sheet thickness from the surface is in the range of 10 to 25, the average value of the value rr (r = (r + r + r × 2) / 4) is 0.05 or more, the absolute value of the anisotropy index in the plane of the value rΔr (Δr = (r + rr × 2) / 2) is 0.30 or less, and the average diameter of the crystal grains is 50 μm or less.

[0020] For metallurgical or productivity reasons, it is also possible to consider quenching the strip after hot rolling.

[0021] For example, reversing mills followed by "pools" are known, in which the metal with the final hot gauge is immersed and cooled ("Mise en forme de l'aluminium-Laminage-Patrick Deneuville, (©) Techniques de l'Ingenieur-2010").

[0022] WO 2019 / 241514 relates to a system and method for quenching a metal strip after rolling. The application relates to a system and method for quenching a metal substrate, which includes cooling an upper surface and a lower surface of the metal substrate until the temperature of the strip is cooled to an intermediate temperature. Cooling of the upper surface of the metal substrate is discontinued when the temperature of the strip reaches the intermediate temperature, and cooling of the lower surface of the metal substrate is continued until the metal substrate reaches a target temperature, which is lower than the intermediate temperature.

[0023] French patent application FR 2 378 579 A1 relates to a method for rapid cooling of continuously cast material in the form of round bars or slabs, which are placed on a roller conveyor and subjected to water spraying. According to this application, this method is characterized in that the bar is moved in a reciprocating motion during the entire duration of cooling, the path of this motion being greater in the withdrawal direction than in the opposite direction.

[0024] US Patent No. 6,309,482 relates to the on-line combination of a reversing rolling mill (Steckel mill) and its coiler furnace with a controlled accelerated cooler immediately downstream of the furnace, and the associated process, which allows for sequential rolling of steel in a reversible manner to obtain an overall reduction of at least about 3:1.

[0025] U.S. Pat. No. 9,643,224 relates to an apparatus for cooling a rolled product, preferably for cooling during cold rolling, which includes a nozzle for applying a coolant onto the rolled product, and a cooling chamber in fluid communication with the nozzle and extending approximately parallel to the strip discharge plane, for applying a coolant onto the rolled product.

[0026] EP 2979769 relates to a method and facility for producing steel plate, which can guarantee high quality steel plate with less quality variation. The patent also relates to a method for producing steel plate, which includes, in that order, a hot rolling step, a straightening step and an accelerated cooling step. [Prior art documents] [Patent documents]

[0027] [Patent Document 1] International Publication No. 2015 / 58902 [Patent Document 2] European Patent No. 2991783 [Patent Document 3] International Publication No. 2008 / 89827 [Patent Document 4] International Publication No. 2016 / 012691 [Patent Document 5] International Publication No. 2018 / 011245 [Patent Document 6] European Patent No. 1165851 [Patent Document 7] US Patent Application Publication No. 2016 / 0201158 [Patent Document 8] European Patent No. 1375691 [Patent Document 9] European Patent No. 0786535 [Patent Document 10] Japanese Patent Application Laid-Open No. 2015-067857 [Patent Document 11] International Publication No. 2019 / 241514 [Patent Document 12] French Patent Application Publication No. 2378579 [Patent Document 13] U.S. Patent No. 6,309,482 [Patent Document 14] U.S. Patent No. 9,643,224 [Patent Document 15] European Patent No. 2979769 [Non-patent literature]

[0028] [Non-Patent Document 1] "Mise en forme de l'aluminium-Laminage-Patrick Deneuville, (Copyright) Techniques de l'Ingenieur-2010" Summary of the Invention [Problem to be solved by the invention]

[0029] The problem that the present invention aims to solve is to improve the productivity of a reversing rolling mill by improving the productivity of the metallurgical quality and / or other processing steps without compromising the metallurgical quality of the resulting product. In particular, there is a demand in the automotive industry for a highly productive process to provide 6xxx alloy sheet material of better quality, especially in terms of mechanical strength, formability and assembly, and surface appearance after painting. [Means for solving the problem]

[0030] A first object of the present invention is to provide a reversing hot rolling mill comprising two work rolls, an upper work roll (21) and a lower work roll (22), and at least one cooling system for cooling a blank (11), said blank (11) moving on rollers (23) and passing through the reversing hot rolling mill between the two work rolls (21 and 22), said cooling system consisting of two cooling devices, namely an upper cooling device for the blank (11) and a lower cooling device for the blank (11), the upper cooling device includes at least one inclined portion (30) of a nozzle (35) arranged substantially parallel to the axis of the upper work roll, the nozzle (35) distributing a cooling fluid jet (36) onto the upper surface of the blank (11); the lower cooling device is disposed between the rollers or between the lower work roll and the nearest roller, and includes at least one inclined portion of a nozzle that is substantially parallel to the axis of the lower work roll, the nozzle dispersing a cooling fluid jet onto the lower surface of the blank, the axis of the cooling fluid jet being oriented substantially perpendicular to the lower surface of the blank; The reversing hot rolling mill is characterized by the above.

[0031] Another object of the present invention is to provide a method for hot rolling an aluminum alloy, comprising the steps of: a. providing an aluminum alloy rolled plate using one or more aluminum alloys at a hot rolling entry temperature; b. performing multiple passes of hot rolling and / or cooling using the hot rolling mill of the present invention, wherein the cooling system is used at least once; c. transferring the blank (11) or the finished product in the form of a plate or strip at the hot rolling exit temperature for the subsequent part of the processing method; The method includes the following successive steps:

[0032] Yet another object of the present invention is to provide a method for rolling AA6xxx series aluminum alloys, comprising: a. Casting of rolled plates made of AA6xxx alloys; b. A homogenization step of the rolled plate, optionally followed by a reheating step; c. a first hot rolling step for converting the rolled plate into a blank having a first exit thickness based on a first temperature at the start of the hot rolling; d. cooling the blank thus obtained from its average temperature to the second temperature at the start of the second hot rolling at a typical average cooling rate of approximately V=C / e, where V is in °C / s, e is the thickness of the blank in mm, and C is a constant between 400 and 1000 °C / s x mm, preferably between 600 and 900 °C / s x mm, more preferably between 700 and 800 °C / s x mm; e. a second hot rolling step for converting the thus cooled blank into a strip of final hot rolled thickness under deformation and temperature conditions such that the strip recrystallizes to at least 50%; f. cold rolling step from strip to sheet; The rolling method includes the following successive steps:

[0033] Yet another object of the present invention is to provide a method for producing an equivalent holding time at 560°C.

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[0034] [Figure 1] 1 is a perspective view of a blank passing through a rolling mill, without showing the cooling system. [Figure 2] 1 is a top view of a blank passing through a rolling mill according to the present invention, showing the convex envelope of the surface directly subjected to the dissipation of the cooling fluid jet upon initial impact on the blank. [Figure 3] 1 is a bottom view of a blank passing through a rolling mill according to the present invention, showing the convex envelope of the surface directly subjected to the dissipation of the cooling fluid jet upon initial impact on the blank. [Figure 4] 10 is another top view of the blank passing through the rolling mill in a preferred embodiment of cooling fluid jet direction, showing the cooling fluid jets upon initial impact on the blank. FIG. [Figure 5a] FIG. 1 is a diagram of a nozzle with a fast response gate valve. [Figure 5b] FIG. 1 is a diagram of a nozzle with a fast response gate valve. [Figure 6] 1 is a vertical cross-sectional view of an embodiment of a rolling mill according to the present invention. [Figure 7] FIG. 4 is a longitudinal sectional view of another embodiment of a rolling mill according to the present invention. [Figure 8] FIG. 4 is a longitudinal sectional view of another embodiment of a rolling mill according to the present invention. [Figure 9] FIG. 4 is a longitudinal sectional view of another embodiment of a rolling mill according to the present invention. [Figure 10] FIG. 4 is a longitudinal sectional view of another embodiment of a rolling mill according to the present invention. [Figure 11a] 1 is a cross-sectional view of an embodiment of a rolling mill according to the present invention. [Figure 11b] 1 is a cross-sectional view of an embodiment of a rolling mill according to the present invention. [Figure 12] FIG. 4 is a longitudinal sectional view of another embodiment of a rolling mill according to the present invention. [Figure 13] FIG. 4 is a longitudinal sectional view of another embodiment of a rolling mill according to the present invention. [Figure 14] FIG. 4 is a longitudinal sectional view of another embodiment of a rolling mill according to the present invention. [Figure 15] FIG. 4 is a longitudinal sectional view of another embodiment of a rolling mill according to the present invention. [Figure 16] FIG. 1 is a diagram of the principle of control of the cooling system. [Figure 17] 1 is an example of temperature inhomogeneity of the blank for a prior art method. [Figure 18] 1 is an example of temperature non-uniformity in a blank by utilizing a rolling mill according to the present invention in accordance with a preferred embodiment. [Figure 19] 1 is an example of rapid cooling of a 114 mm AA6xxx aluminum plate from 470° C. to 420° C. in 8 seconds with a hot rolling emulsion using a rolling mill according to another preferred embodiment of the present invention. [Figure 20] 1 is an example of rapid cooling of a 140 mm AA6xxx aluminum plate from 470° C. to 420° C. in 10 seconds with a hot rolling emulsion using a rolling mill according to another preferred embodiment of the present invention. [Figure 21] 1 is a photograph of the surface quality of the roping described in Example A without the use of the present invention. [Figure 22] 1 is a photograph of the surface quality of the roping described in Example B without the use of the present invention. [Figure 23] 1 is a photograph of the surface quality of a roping using the present invention as described in Example D. [Figure 24] 1 is a photograph of the surface quality of a roping using the present invention as described in Example E. [Figure 25] 1 is a metallography showing the recrystallization rate under different conditions. [Figure 26] 1 is a graph showing the effect of solution treatment duration on mechanical properties. DETAILED DESCRIPTION OF THE INVENTION

[0035] All aluminum alloys referred to below, unless otherwise noted, are designated in accordance with the rules and names defined by the Aluminum Association in its Registration Record Series, periodically published.

[0036] The metallurgical tempers in question are designated according to European standard EN-515.

[0037] The static mechanical properties in tension are determined by tensile testing according to the NF EN ISO 6892-1 standard.

[0038] Unless otherwise stated, the definitions in the EN 12258 standard apply.

[0039] A blank is herein defined as an intermediate aluminum alloy product obtained by rolling a rolled plate, such as a cast ingot or plate, optionally scalped and optionally clad with one or more aluminum alloys, for the production of a finished aluminum alloy product in the form of a plate, strip or sheet, optionally clad with one or more aluminum alloys. A blank is thus a rolled product having a thickness intermediate between that of a rolled plate and a finished product.

[0040] Unless otherwise indicated, the term "rolling mill" herein refers to a "reversing mill."

[0041] Unlike the prior art, which increases the productivity of a reversing mill by increasing the capacity of the mill in terms of rolling stress and / or torque, or improves the productivity of a preceding or subsequent step, the present inventors have succeeded in improving the productivity of a reversing mill without resorting to these solutions.

[0042] The inventors have determined that most aluminum alloys tend to overheat with each pass, especially considering their hardness, and it is then necessary to slow down the rolling mill, for example by reducing the pass rate or by providing a waiting time between each rolling pass.

[0043] According to the present invention, it has been determined that cooling the blank between the hot rolling steps makes it possible to improve the productivity of the hot rolling mill or to create new, more economical manufacturing methods by eliminating several production steps, while keeping the metallurgical quality of the product the same or improving it. Thus, cooling the blank between rolling on a reversing mill can also, unexpectedly, make it possible to impart complementary physical properties to the rolled finished product, such as mechanical properties, surface condition or corrosion resistance.

[0044] The reverse hot rolling mill of the present invention includes two work rolls, an upper work roll (21) and a lower work roll (22), and at least one cooling system for cooling a blank (11), which moves on rollers (23) and passes through the reverse hot rolling mill between the two work rolls (21 and 22), and the cooling system is composed of two cooling devices, namely, an upper blank (11) cooling device and a lower blank (11) cooling device. Many other components and systems of a hot rolling mill well known to those skilled in the art, such as, but not limited to, backup rolls, motors, supports, shafts, etc., are not shown in the figures.

[0045] The upper cooling device includes at least one angled portion (30) of a nozzle (35) arranged substantially parallel to the axis of the upper work roll (21), the nozzle (35) distributing a cooling fluid jet (36) onto the upper surface of the blank (11).

[0046] The lower cooling device is disposed between the rollers (23) or between the lower work roll (22) and the nearest roller, and includes at least one inclined portion (40) of a nozzle (45) that is substantially parallel to the axis of the lower work roll (22), the nozzle (45) spraying a cooling fluid jet (46) onto the lower surface of the blank (11), the axis of the cooling fluid jet (46) being directed substantially perpendicular to the lower surface of the blank (11).

[0047] Figure 1 shows a blank (11) passing through a reversing hot rolling mill (the cooling system is not shown in this view). Figure 1 shows the edge (111), the edge portion (1111) and the end portion (112). The blank (11) is represented in simplified form as a parallelepiped, but in reality it is more complex.

[0048] The edge (112) corresponds to the portion of the blank (11) that first engages and last disengages from the holding portions of the rolls (21) and (22). The edge (112) is depicted in simplified form as a parallelepiped in FIG. 1 . Those skilled in the art are familiar with the edge (112), as it must be removed to ensure the production and quality of the final product. The edge (112) generally undergoes a rounded or bisecting deformation during hot rolling, a phenomenon known to those skilled in the art as crocodiling. The edge (112) also corresponds to regions of the blank where rolling is not uniform along its length. The edge (112) may also include regions corresponding to the transitional states at the beginning or end of the casting that produced the plate. The length of the edge (112) depends on the alloy, the rolling and casting conditions, and the end application. This removal of the edge (112) can occur on a shear installed on the hot row or later in the manufacturing process, depending on the specific constraints of the final product and its manufacturing method. The length of the edge (112) can typically be a maximum of 100 mm, 200 mm, 300 mm, 400 mm, 500 mm, or 600 mm. The edge (1111) is the surface that connects the upper surface of the blank (11) in contact with the upper roll (21) and the lower surface of the blank (11) in contact with the lower roll (22) without becoming part of the edge (112). The edge (111) is the portion of the blank (11) that is near the edge (1111), excluding the edge (112). The edge (111) is well known to those skilled in the art, as it must be removed to ensure the manufacturing and quality of the finished product. In industrial reality, the edges (111) and marginal edges (1111) have a much more complex shape than that diagrammed in Figure 1, since cracks and creases, well known to those skilled in the art, often appear there. These deformations must be removed. The edges (111) are not rolled homogeneously in width, given the proximity of the edges (1111), and must be removed to guarantee the properties of the final product.This removal of edge (111) can occur at the end of hot rolling or later in the manufacturing process, depending on the final product and the specific constraints of its manufacture. The width of edge (111) can typically have a maximum value of 25 mm, 50 mm, 50 mm, 75 mm, 100 mm, 125 mm, 150 mm, 175 mm, 200 mm or 250 mm.

[0049] For each cooling system, an upper convex envelope (52) and a lower convex envelope (62) are defined as the convex envelopes of the respective surfaces (51) and (61) directly subjected to the dissipation of the cooling fluid jets (36) and (46), respectively, upon initial impact on the blank (11). An example of the convex envelope (52, 62) of the dissipated surfaces (51, 61) is illustrated by Figures 2 and 3, which do not show the cooling systems. Bounce and spillage are not considered in the convex envelope. A set is convex if, for every segment whose end is within the set, every point of the segment is completely contained within the set. The convex envelope of a set is the smallest convex set that contains it. The convex envelope is determined by separating different cooling systems according to their functions. Two cooling systems are separated if there is a roll (21) or (22) between them. Figure 7 illustrates a non-limiting example including a second cooling system. In this example, the convex envelope of each system is analyzed separately, with one system cooling the blank (11) before passing between rolls (21) and (22) and the other system cooling the blank after passing between rolls (21) and (22). Two cooling systems are separated if there are at least two, or at least three, or at least four, or at least five rollers (23) between which there are no cooling nozzles (45) for the underside of the blank. Figure 15 shows an example with three cooling systems: two on either side of the reverse hot rolling mill, and a third cooling system further away, which in this non-limiting example serves to rapidly cool the blank (11) before transferring it to the second hot rolling mill with its rolls (25) and (26). It is noted that while Figure 15 shows two blanks in two locations, these blanks may not be present at the same time.

[0050] As illustrated in FIG. 2, for each cooling system, the maximum distance D55 from the convex envelope (52) to the roll (21) is the maximum distance of any point on the convex envelope (52) to a straight line C1, which is the projection of the axis of rotation of the roll (21) on the top surface of the blank (11), minus the radius R1 of the roll (21).

[0051] As illustrated in FIG. 2, for each cooling system, the minimum distance D57 of the convex envelope (52) to the roll (21) is the minimum of the distances of any points of the convex envelope (52) to the line C1, which is the projection of the axis of rotation of the roll (21) on the top surface of the blank (11), minus the radius R1 of the roll (21).

[0052] As illustrated in FIG. 3, for each cooling system, the maximum distance D65 from the convex envelope (62) to the roll (22) is the maximum distance of any point of the convex envelope (62) to a line C2, which is the projection of the axis of the roll (22) on the lower surface of the blank (11), minus the radius R2 of the roll (22).

[0053] As illustrated in FIG. 3, for each cooling system, the minimum distance D67 of the convex envelope (62) to the roll (22) is the minimum of the distances of any point of the convex envelope (62) to the line C2, which is the projection of the axis of the roll (22) on the lower surface of the blank (11), minus the radius R2 of the roll (22).

[0054] For each cooling system, the area opposite the rolling mill (54) and the area adjacent to the rolling mill (53) are surfaces that form part of a half-plane that includes the upper convex envelope (52) of the blank (11), considered as a simplified parallelepiped in FIG. 1, and is bounded by the straight line C1.

[0055] For each cooling system, as illustrated in FIG. 2, the opposite region (54) of the rolling mill is a half-plane that does not include the convex envelope (52) and is bounded by a line E1 that is parallel to the line C1 and at a maximum distance D55 from the line C1 plus the radius R1 of the roll (21).

[0056] For each cooling system, the area (53) adjacent to the rolling mill is bounded by a line C1 and by a line D1 parallel to the line C1 at a minimum distance D57 from the line C1 plus the radius R1 of the roll (21).

[0057] The direction S is the direction of movement of the blank (11).

[0058] According to FIG. 2, for each cooling system, the distance D56 along the direction S of the convex envelope (52) is the length D55 minus the length D57.

[0059] According to FIG. 3, for each cooling system, the distance D66 along the direction S of the convex envelope (62) is the length D65 minus the length D67.

[0060] In a non-limiting embodiment illustrated by Figure 6, the upper cooling device consists of one angled section (30) of a nozzle (35) positioned substantially parallel to the axis of the upper work roll (21), the nozzle (35) distributing a cooling fluid jet (36) onto the upper surface of the blank (11). The lower cooling device illustrated by Figure 6 consists of two angled sections (40) of a nozzle (45) positioned between the rollers (23) and substantially parallel to the axis of the lower work roll (22), the nozzle (45) distributing a cooling fluid jet (46) onto the lower surface of the blank (11), the axis of the cooling fluid jet (46) being directed substantially perpendicular to the lower surface of the blank (11). In one embodiment illustrated by Figure 10, the lower cooling device consists of one angled section of a nozzle (45) positioned between the lower work roll (22) and the nearest roller (23).

[0061] For example, the embodiments illustrated non-limitingly by Figures 8 and 12 show top cooling devices consisting of two and three ramps (30) of nozzles (35), respectively.

[0062] Preferably, the lower nozzle (45) generates a cooling fluid jet (46) that does not directly reach either the roller (23) or the roll (22) in the presence of the blank (11), and is preferably approximately tangential to the roller (23), the distance D67 being preferably greater than the radius of the lower roll (22), more preferably greater than the diameter of the lower roll (22); and / or the upper nozzle (35) generates a cooling fluid jet (36) that does not directly reach the upper work roll (21), and preferably the distance D57 is greater than the radius of the upper roll (21), more preferably the distance D57 is greater than the diameter of the upper roll (21). In one embodiment illustrated by Figure 5b, the cooling fluid jets (46) do not directly reach the roller (23) so that these jets only affect the temperature of the blank (11). In one embodiment illustrated by FIG. 10 , where the inclined portion 40 is disposed between the roll 22 and the roller 23, the cooling fluid jets 46 do not reach the roll 22 directly, so that they only affect the temperature of the blank and do not disrupt the temperature field in the roll 22, which is an important factor for hot rolling quality. It is advantageous for the distance D67 to be greater than the radius R1 of the lower roll 22, preferably the diameter of the lower roll 22, to prevent the rebound of the fluid jets 46 from reaching the roll 22 and disrupting its temperature field. Similarly, it is advantageous for the area of ​​the lower surface of the blank 11 that is exposed to the dissipation of the lower cooling fluid jets 46 to be maximized to improve heat exchange. To maximize the surface that is exposed to the dissipation of the jets 46 without touching the roller 23, it is advantageous for the jets 46 to pass by the roller 23 without touching it, as illustrated by FIG. 5 b. These lower jets (46) are therefore preferably approximately tangential to the rollers (23). The invention thus makes it possible to maximize the surface subjected to dissipation in order to increase the effective surface for heat exchange. The jets (36) advantageously do not contact the rolls (22) so as not to disturb the temperature field in the rolls (21), which is an important factor in the quality of hot rolling.It is advantageous for the distance D57 to be greater than the radius R1 of the upper roll (21), preferably the distance D57 to be greater than the diameter of the upper roll (21), to avoid rebounding of the fluid jet (36) from reaching the roll (21) and potentially disrupting its temperature field.

[0063] Nozzles (24), illustrated in Figure 6 and dedicated to rolls (21) and (22), can be installed to cool or lubricate these mechanisms according to their specific needs, independent of blank (11). In one embodiment not illustrated, a specific nozzle can be installed to cool roller (23). The location of nozzles (24) in Figure 6 is merely illustrative and not limiting.

[0064] Preferably, the lower nozzle 45 is below a plane passing through the axis of rotation of the roller 23 located near the nozzle 45, and / or the lower nozzle 45 is protected by a part 47 having an opening for the passage of the cooling fluid jet 46, and / or the upper nozzle 35 is protected by a part 37 having an opening for the passage of the cooling fluid jet 36. Protecting the nozzles 35 and 45 is advantageous because hot rolling can induce openings in the end 112 of the blank 11, which those skilled in the art refer to as "alligator splits," and which can result in the blank 11 impinging on the nozzle. The blank 11 can also form bridges or boats during hot rolling, i.e., the blank 11, instead of being substantially planar, can bend longitudinally upon exiting the rolling mill with its end pointing up or down. Therefore, protecting the nozzles (35) and (45) from the blank (11) is advantageous to avoid damage to said nozzles. Non-limiting examples of parts (37) and (47) that protect the nozzles (35) and (45) are illustrated in Figures 8, 9, and 13. Figure 7 shows a non-limiting example in which only the nozzles (35) are protected by the protective part (47). When the rollers (23) are very close to each other, it is possible to economically protect these nozzles without installing the protective part (47) by placing the nozzles (45) below the plane of the axes of the rollers (23), as illustrated in Figures 6 and 7.

[0065] Preferably, each nozzle (35) and (45) is individually refilled by a fast-response gate valve (49), advantageously with a response time of less than 1 second, preferably less than 0.5 seconds, and more preferably less than 0.2 seconds. Figures 5a and 5b show non-limiting examples of fast-response gate valves (49) installed between the respective ramps (30) and (40) and the respective nozzles (35) and (45). Refilling the nozzles individually using fast gate valves is advantageous because it allows specific cooling of each point on the upper and lower surfaces of the blank (11). These response times, in particular, allow for reliable dissipation to the end (112) of the blank (11) to adjust its temperature in a manner that facilitates its engagement between the rolls (21) and (22). The temperature at the end (112) of the blank (11) can then be adapted to facilitate its engagement in a reversing hot rolling mill. Similarly, it is possible to adapt the temperature at the edge (111) in order to limit cracking, which could reduce the effective width of the blank and even cause it to break. It is therefore also possible to optimize the temperature of other parts of the blank (11) depending on the properties desired in the finished product or in subsequent production steps. This is advantageous, for example, for better control of the properties of the final product, such as the anisotropy in width for AA3104 alloy products or the uniformity of the mechanical properties for AA6xxx alloy products. Finally, by specifically cooling each point of the blank (11), it is also possible to control the differential expansion and thus the flatness of the blank (11).

[0066] In one embodiment, the nozzles (35) and (45) can generate the cooling fluid jets (36) and (46) in a flat, conical, and / or cylindrical shape. If the jets are cylindrical, the roll cross section is preferably circular. In one embodiment, the nozzles (35) and (45) can generate the cooling fluid jets (36) and (46) by atomization. Preferably, the nozzles (35) and (45) can generate the cooling fluid jets (36) and (46) in a solid cone shape, called a conical jet. The conical jets (46) and (36) are superior to flat or cylindrical jets. In fact, the conical jets allow for better distribution of the cooling fluid on the blank (11). This therefore allows for more uniform heat exchange, thereby resulting in a blank (11) with a temperature inhomogeneity of, for example, less than 20°C, preferably less than 10°C.

[0067] Preferably, the conical cooling fluid jet 46 has a cone angle of 90°. This angle may be limited, for example to 60°, by the presence of rollers 23, so as not to dissipate onto those rollers 23, especially if the nozzle 45 is located below the plane passing through the axes of the rollers 23. If the rollers 23 are very close together, it may be preferable to place the nozzle 45 above the plane passing through the axes of the rollers 23 in order to dissipate onto a larger surface 61. In FIG. 5b, the nozzle 451 is located below the plane of the axes of the rollers 23 and generates the cooling jet 461. In FIG. 5b, the nozzle 452 is located above the plane of the axes of the rollers 23 and generates the cooling jet 462; the protective element 47, which should preferably be installed in this situation, is not shown. Jet 462 therefore spreads over a larger surface of blank 11 than jet 461, although this is not shown.

[0068] Preferably, for each cooling system, at least one device (38) for evacuating the cooling fluid from the upper surface of the blank (11) is installed above the blank. Non-limiting examples of such devices (38) are shown in Figures 8, 10, or 12. The device (38) can be installed above the area (54) opposite the rolling mill and / or above the area (53) adjacent to the rolling mill. Preferably, the device (38) is an air blast that forces the cooling fluid toward one of the edges (111) of the blank (11), preferably imparting sufficient velocity to the cooling fluid to prevent it from flowing over the edge (1111). The device (38) makes it possible to prevent the flow of the cooling fluid over the entire upper surface of the blank (11). This contributes to ensuring controlled cooling with excellent repeatability and reproducibility of the temperature inhomogeneity of the blank (11). Preventing the cooling fluid from leaking out over the edge (1111) contributes to thermal control of the periphery of the blank (11), in particular making it possible to prevent the periphery from being overcooled, thus limiting the occurrence of cracks in the edge (111). If the upper cooling device is located near the roll (21), the cooling fluid discharge device (38) is advantageously complemented or replaced by the roll (21) which serves as a weir blocking the outflow of cooling fluid. This makes it possible, in particular, to reduce the energy consumption of the device (38). A non-limiting example of a configuration in which the device (38) for discharging cooling fluid near the roll (21) is replaced by the roll (21) is illustrated by FIG. 10.

[0069] In one embodiment, the conical jet of the upper cooling device (36) has a cone angle α of at most 20°, preferably substantially 15° or less, with the cone of said conical jet having a substantially vertical axis. This configuration makes it possible to limit the outflow of cooling fluid onto the blank (11). Preferably, a cooling system with at least one such conical jet is surrounded by a cooling fluid ejection device (38), as illustrated, but not limited to, in FIG. 12. The cone angle α is illustrated in FIG. 5a, where the cone angle α is the cone angle of the cooling fluid jet generated by the nozzle.

[0070] In another embodiment, the conical jet of the upper cooling device (36) is inclined relative to the vertical. The inclination angle β is illustrated in FIG. 5a and is the angle between the axis of the nozzle and a line V perpendicular to the upper surface of the blank (11). Preferably, the difference β-α / 2 is greater than -20°, preferably substantially greater than -15°, and more preferably positive or zero. Preferably, when the difference β-α / 2 is negative, a cooling fluid discharge device (38) is installed to prevent overflow on the surface of the blank (11). When the cooling fluid jet of the upper cooling device (36) is near the work roll (21), the axis of the cooling fluid jet (36) is advantageously oriented to approach the diffusion surface (51) of the work roll (21) to utilize the weir effect of the roll (21). This configuration also makes it possible to increase the diffusion surface (51) and thereby increase the cooling capacity of the cooling system. When the cooling fluid jets are spaced apart from the work roll, it is advantageous to group the inclined portions of the upper cooling device (30) together and orient the axes of the cooling fluid jets (36) so as to bring their respective dissipating surfaces (51) closer together. This configuration is advantageous because it concentrates the cooling fluid within at least a portion of the overlapping area of ​​the jets (36), thereby allowing the cooling fluid to be discharged onto the periphery of the blank (11) with sufficient velocity to prevent it from flowing out onto the edge (1111) of the blank (11), thereby preventing excessive cooling of the edge (111) of the blank (11).

[0071] 8 is a non-limiting example of the previous embodiment. The nozzle (351) near the work roll has its axis oriented toward the work roll (21), and the difference β-α / 2 is greater than -20°. The nozzle (352) is oriented vertically, and the angle α of its conical jet (36) is less than 20°.

[0072] 9 is another non-limiting example of the previous embodiment, in which the nozzles (351) near the work roll are all angled to bring the surface (51) receiving the diffusion towards the work roll, and the difference β-α / 2 of the conical jets is positive or zero to avoid the flow of cooling fluid onto the blank (11).

[0073] FIG. 12 is another non-limiting example of the previous embodiment with vertical conical cooling jets (36) with a cone angle α of less than 20°.

[0074] Figure 13 is another non-limiting example of the previous embodiment. The ramps (303) and (304) are paired, and the nozzles (353) and (354) are oriented so that the surfaces (513) and (514) receiving the diffusion are close together, as illustrated by Figure 4. The difference β-α / 2 is positive or zero.

[0075] Preferably, for each cooling system, the upper convex envelope (52) receiving the diffusion faces the lower convex envelope (62) receiving the diffusion, with a tolerance of twice the diameter of the upper work roll (21), preferably equal to one; preferably, the convex envelopes (52, 62) are substantially contiguous. The determination of the convex envelopes is performed by separating the different cooling systems of the present invention. FIG. 7 shows a non-limiting example in which a second cooling system is present. In this case, the convex envelope of each system is analyzed separately, since one system cools before passing between the rolls (21) and (22) and the other system cools after passing between the rolls (21) and (22). FIG. 15 shows an embodiment with three cooling systems, two on either side of the reverse hot rolling mill and a third cooling system further away, which serves for fast cooling before merging with the second hot rolling mill, in this non-limiting example, with rolls (25) and (26). This arrangement is advantageous because it contributes to the thermal uniformity of the blank 11. Having the upper and lower convex envelopes 52, 62 of each cooling system facing each other is extremely advantageous because it allows for uniform cooling throughout the thickness of the blank 11, which contributes to controlling the flatness of the blank 11, an important characteristic for blanks that are flat products.

[0076] Preferably, the nozzle assemblies (35) and (46) have a maximum flow rate of 1500 l / min / m 2, preferably 600 to 1200 l / min / m 2 The blank (11) can be provided with a surface flow rate of cooling fluid per side of the blank (11). This fluid may be propelled by a jet gas. The cooling fluid can be water, deionized water, liquefied or liquefied gas, preferably water, preferably an emulsion of deionized water with oil and rolling additives that serve to lubricate the blank (11) and the rolls (21) and (22). Preferably, the deionized water has a resistivity greater than 105 kΩ cm.

[0077] In one embodiment, the nozzle of the top cooling device (35) is movable, preferably attached to a mechanism that maintains the rolls (21) and maintains it at a fixed distance from the upper surface of the blank (11). This allows for better repeatability of the cooling of the blank (11). In another embodiment, the nozzle (35) is not movable. In this less costly non-moving embodiment, the nozzle (35) spraying at the edge (111) or spraying near the edge (111) must be controlled accordingly, for example, if the nozzle (35) generates a conical jet (36). Indeed, in the case of a conical jet (36) projected by a fixed nozzle (35), the distribution of cooling fluid on the edge (111) expands as the blank thickness decreases during successive passes of the reverse hot rolling design. Figures 11a and 11b are non-limiting examples of this situation. The blank (11) is shown at the beginning of hot rolling in Figure 11a and at the end of hot rolling in Figure 11b, with the same number of top nozzles (35) generating cooling fluid jets (36) in each run. Due to the conical shape of the jets (36) and the reduced thickness of the blank (11), the edge (111) is unspared at the beginning of rolling as illustrated in Figure 11a, while it is partially sparged at the end of rolling as illustrated in Figure 11b. Thus, in one embodiment, at the beginning of hot rolling, and preferably throughout the duration of hot rolling, the intersection between the top surface (51) directly subjected to the sparging of the cooling fluid jets (36) with the top surface of the edge (111) is empty. Thus, in one embodiment, at the start of hot rolling, and preferably throughout the duration of hot rolling, the intersection between the lower surface (61) directly subjected to the dissipation of the cooling fluid jet (46) with the lower surface of the edge (111) is empty.

[0078] In a preferred embodiment, illustrated by way of non-limiting example in Figure 10, a nozzle (351) near the upper work roll (21) generates a cooling fluid jet (36) with all displacement components projected in the displacement direction S of the blank (11) directed towards the rolling mill work rolls (21) and (22). Preferably, the cooling fluid jet (36) of the upper cooling device is conical, and the difference β-α / 2 is positive or zero. In a more preferred embodiment, as illustrated by Figure 6, there is only one upper inclined section (30) and two lower inclined sections (40).

[0079] In a preferred embodiment, illustrated by the non-limiting example of FIG. 6, the upper convex envelope (52) and the lower convex envelope (62) are located near the rolling mill rolls, and preferably the maximum distances D55 and D65 from the convex envelopes (52) and (62) to the rolls (21) and (22) are less than three times the diameter of the largest of the work rolls (21) and (22), and / or the lengths D56 and D66 of the convex envelopes (52, 62) are less than two times, preferably less than one time, the diameter of the largest of the work rolls (21) or (22). This embodiment is advantageous because it allows the blank (11) to be cooled immediately upon leaving the holding section of the rolls (21) and (22), avoiding excessive separation of the blank from the rolls before restarting in the other direction for the next pass of hot rolling. This is particularly advantageous because it improves the productivity of the hot rolling mill. In fact, the speed of the reverse hot rolling mill is often limited to avoid heat buildup that can lead to burning, cracking, alligator cracking, or even breaking of the blank (11).

[0080] In a preferred embodiment, illustrated by the non-limiting example of Figure 7, there is a second cooling system on the other side of the reversing hot rolling mill, which second cooling system is preferably symmetrical to the first cooling system with respect to a plane passing through the axes of the work rolls (21) and (22). This arrangement is advantageous because it allows the blank (11) to be cooled in the same way in each rolling pass, up to its entry into the holding section of the reversing mill and immediately upon its exit from the holding section of the reversing mill.

[0081] In another preferred embodiment illustrated by way of non-limiting example in FIGS. 4 and 13, the upper cooling system includes at least one pair of inclined sections (303 and 304) of the nozzles (353, 354), preferably three pairs of inclined sections (303 and 304), in each pair of inclined sections (303 and 304), the cooling fluid jets (363, 364) are directed oppositely, and the difference β-α / 2 is positive or zero, preferably zero, where α is the cone angle of the cooling fluid jets generated by the nozzles. where β is the inclination angle between the axis of the nozzles (353, 354) and a line V perpendicular to the upper surface of the blank (11). The surfaces (513, 514) of the blank (11) receiving the diffusion from the jets (363, 364) are preferably overlapped by a ratio of 1 / 3 to 2 / 3, preferably 1 / 2. The lower cooling device includes at least one inclined portion (40) of the nozzle (45), preferably eight inclined portions (40), whose cooling fluid jets (46) are conical and whose axes are substantially normal to the blank (11). Preferably, the blank (11) is substantially horizontal. The angle is diagrammed in the general case of FIG. 5a, along with the nozzles (35), inclined portions (30), and cooling fluid jets (36). FIG. 4 illustrates the diffusion surface (51). This configuration is advantageous because it concentrates the cooling fluid within at least a portion of the overlapping region of the jets (36), thereby allowing the cooling fluid to be discharged onto the periphery at a sufficient velocity to avoid overflowing onto the edge (1111) of the blank (11), thereby avoiding excessive cooling of the edge (111) of the blank (11). This reduces or even eliminates the energy consumption of the cooling fluid discharge device (38).

[0082] In another preferred embodiment, non-limitingly illustrated in FIG. 12 , the upper cooling device includes at least one inclined nozzle (35) (30), preferably six inclined nozzles (30), and the lower cooling device includes at least one inclined nozzle (45) (40), preferably eight inclined nozzles (40), all generating conical cooling fluid jets (36) and (46) with axes substantially perpendicular to the blank (11) and with a jet (36) cone angle α of less than 20°, preferably substantially 15°. This device has the advantage of being simpler to manufacture. The conical jet angle limits the horizontal component of the cooling fluid velocity upon impact on the blank (11), thereby limiting the spread of the cooling fluid on the blank (11) and allowing for controlled cooling.

[0083] In another preferred embodiment, illustrated but not limited to, by Figures 14 and 15, the reversing hot rolling mill of the present invention is part of a hot train in which it is preferably followed by a second hot rolling mill, which may be a reversing or tandem rolling mill, as shown diagrammatically with work rolls (25) and (26). In the embodiment illustrated by Figure 14, the cooling system of the reversing hot rolling mill of the present invention is located between the reversing hot rolling mill of the present invention and the second hot rolling mill, and preferably the distance between the cooling system and the second hot rolling mill is sufficient to allow the cooling system of the present invention and the second hot rolling mill to function independently. This arrangement is advantageous because it allows cooling operations to be performed within the production flow without loss of capacity during transfer of blanks from the first reversing hot rolling mill to the second reversing hot rolling mill. The distance between the cooling system and the second hot rolling mill is also important if it is sufficient in relation to the length of the blank, for example, to allow for the selection of different speeds for passing through the cooling system and for passing through the second hot rolling mill. The length of the blank is calculated by EP x LP / e, where EP is the plate thickness, LP is the plate length, and e is the blank thickness between the two rolling mills. In the embodiment illustrated by FIG. 15, there are three cooling systems for the reversing hot rolling mill of the present invention, two of which are located near and on either side of the work rolls (21, 22), and one system is installed between the reversing hot rolling mill of the present invention and the second hot rolling mill. Preferably, the distance between the cooling systems and the second hot rolling mill is sufficient for the cooling system of the present invention and the second hot rolling mill to function independently.

[0084] The present invention provides a method for hot rolling an aluminum alloy, comprising the steps of: a. providing a rolled clad aluminum alloy plate, optionally at a hot rolling entry temperature; b. performing multiple passes of hot rolling and / or cooling using a reversing hot rolling mill according to the present invention, wherein the cooling system is used at least once; c. transferring the blank (11) or finished product in the form of plate or strip at the hot rolling exit temperature for the subsequent part of the hot working process; The present invention also relates to a method comprising the steps of:

[0085] The minimum width of the blank (11) can typically be 100 mm, 200 mm, 300 mm, 400 mm, 500 mm, 700 mm, 800 mm, 900 mm, and 1000 mm, and the maximum width of the blank (11) can typically be 1500 mm, 2000 mm, 2500 mm, 3000 mm, 3500 mm, 4000 mm, 4500 mm, and 5000 mm.

[0086] The minimum thickness of the blank 11 can typically be 5 mm, 6.35 mm, 10 mm, 12 mm, 12.7 mm, 15 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, 110 mm, 120 mm, 130 mm, 150 mm, 200 mm, and 250 mm. The maximum thickness of the blank 11, which is typically close to the maximum thickness of the cast plate, can typically be 300 mm, 350 mm, 400 mm, 450 mm, 500 mm, 550 mm, 600 mm, 650 mm, 700 mm, and 800 mm.

[0087] The minimum length of the blank (11) can typically be 2 m, 3 m, 4 m, or 5 m. The maximum length of the blank (11) can typically be 6 m, 7 m, 8 m, 9 m, 10 m, 15 m, 20 m, 30 m, 40 m, 50 m, 75 m, 100 m, 150 m, 200 m, 300 m, or 400 m. Two constraints act to limit the maximum length of the blank (11). The first constraint is the amount of metal in the rolled plate before the start of hot rolling. In this case, the maximum length is the length of the plate before the start of hot rolling divided by the thickness of the blank at the end of hot rolling multiplied by the thickness of the plate before the start of hot rolling. The second limit on the length of the blank is dictated by the industrial facility in which the hot rolling mill is installed. As a non-limiting example, if an industrial installation consists of a reversing hot rolling mill followed by a tandem hot rolling mill or a second reversing hot rolling mill, the maximum length is imposed by the distance between the reversing rolling mill of the present invention and the tandem rolling mill or the second reversing hot rolling mill, which implies that not all of the length and thickness configurations listed above before and after hot rolling may be feasible depending on the industrial installation.

[0088] The plate is supplied at the hot rolling entry temperature. The plate may have undergone reheating and / or homogenization.

[0089] The reverse hot rolling mill of the present invention performs multiple hot rolling and / or cooling passes using the hot rolling mill. Therefore, cooling without rolling and thus without thickness reduction of the blank may occur. This feature is advantageous because it allows for increased cooling capacity of the cooling system, if necessary. Similarly, rolling passes without cooling may occur, but the method of the present invention includes at least one pass with a single cooling pass in the cooling system of the present invention. Since the plate is supplied at the hot rolling entry temperature, there is preferably no cooling before the first rolling pass. Operations such as end cutting, edge forming, cutting the blank into smaller blanks, waiting the blank, and rotating the blank to change the hot rolling orientation of the blank (11) or plate are normal operations during hot rolling. The examples of steps mentioned are not limiting. The presence of such normal operations does not limit the scope of the present invention, since they are not interruptions to hot rolling and are part of the normal operation of hot rolling.

[0090] The blank is then transferred to the hot rolling exit temperature of the reversing rolling mill according to the invention. The hot rolling exit temperature is preferably at least 200°C, preferably at least 220°C, suitably at least 240°C, and suitably at least 260°C. This hot rolling exit temperature is compatible with the implementation of a second hot rolling. The blank (11) can be transferred to all the usual steps on the hot train, i.e., to the hot tandem rolling mill, the second reversing hot rolling mill, the hot coiling or the hot reeling.

[0091] Preferably, the blank comprises an aluminum alloy of the AA6xxx, AA5xxx, AA7xxx, AA3xxx, or AA2xxx series. Preferably, the blank comprises an aluminum alloy of the AA3003, AA3004, AA3207, AA3104, AA4017, AA4025, AA5006, AA5052, AA5083, AA5086, AA5088, AA5154, AA5182, AA5251, AA5383, AA5754, AA5844, AA6005, AA6009, AA6013, AA6014, AA6016, AA6022, AA6056, AA6061, AA6111, AA6181, AA6216, AA6316, AA6451, AA6501, AA6502, or AA6603 AA6605, AA6607, AA7072, AA7075 and alloys with the following composition in weight %: Si less than 0.5, preferably less than 0.3, Fe less than 0.7, preferably less than 0.3, Mn less than 1.9, preferably between 1 and 1.5, Cu less than 1.5, preferably between 0.5 and 1, preferably between 0.5 and 0.8, Ti less than 0.15, preferably less than 0.1, Mg less than 0.5, preferably less than 0.3, preferably less than 0.05, the balance being aluminium and unavoidable impurities each at a maximum of 0.05, with a total of up to 0.15. Optionally, the blank is clad on one or both sides with one or more aluminium alloys of the AA1xxx, AA4xxx or AA7xxx series and preferably AA4004, A4104, AA4045, AA4343, AA7072.

[0092] Preferably, the surface temperature non-uniformity of the blank (11) after release from the holding section of the rolling mill and cooling device is less than 20°C, and preferably less than 10°C. This property obtained by the cooling system of the present invention is useful for improving the repeatability of the metallurgical properties of the product. The non-uniformity of the blank (11) is defined as the difference between the temperature of the highest point of the blank (11) and the temperature of the lowest point of the blank (11) except on the edge (111) and / or except on the end (112), and alternatively as the difference between the temperature of the highest point of the blank (11) and the temperature of the lowest point of the blank (11).

[0093] In a hot rolling mill not equipped with the present invention, the edge (111) is naturally cooler than the rest of the blank (11), taking into account the heat exchange surface of the edge (1111). The lowest temperature at the edge (111) is one cause of splits or cracks on the edge, which can reduce the effective width of the blank or induce its fracture. Therefore, the edge (111) of the blank (11) is preferably cooled less than the rest of the blank by dissipating less heat to the edge than to the rest of the blank (11). Preferably, the nozzles (35) and (45), whose jets (36) and (46) can spray the edge (111), are closed to prevent spraying to the edge (111). Figures 11a and 11b show a non-limiting example of a cross section along a plane perpendicular to the direction S passing through the upper inclined portion (30) and the lower inclined portion (40). Some of the top nozzles (35) and bottom nozzles (45) are closed to prevent spraying onto the edge (111).

[0094] In a hot rolling mill not equipped with the present invention, the end portions (112) are naturally cooler than the rest of the blank (11), taking into account the additional heat exchange surfaces at the end portions. The lower temperature of the end portions (112) is one cause of rejection of the blank during hot rolling. Therefore, in a rolling mill equipped with the present invention, the end portions (112) are preferably cooled less than the rest of the blank (11) by dissipating less heat into the end portions (112) than into the rest of the blank (11). Preferably, the nozzles (35) and (45) through which the jets (36) and (46) can spray onto the end portions (112) are closed when these end portions pass. This function can be preferably performed by individual refilling of each nozzle (35) and (45) by a fast-response gate valve (49) advantageously having a response time of less than 1 second, preferably less than 0.5 seconds, and more preferably less than 0.2 seconds. The fast response gate valve (49) is illustrated by the non-limiting example of Figures 5a and 5b. Thus, in one embodiment, the intersection between the upper surface (51) directly subjected to the dissipation of the cooling fluid jets (36) with the upper surface of the end (112) is empty, preferably for the entire duration of the hot rolling. Thus, in one embodiment, the intersection between the lower surface (61) directly subjected to the dissipation of the cooling fluid jets (46) with the lower surface of the end (112) is empty, preferably for the entire duration of the hot rolling.

[0095] The cooling fluid is preferably in a vapor film state on the blank. Vapor filming is a thin vapor film that appears between the fluid and a surface at a sufficiently high temperature (Leidenfrost effect). This is advantageous because it ensures a more homogeneous heat exchange than in situations where there are areas of the surface where the fluid is not in a vapor film state.

[0096] Preferably, the thermal model calculates the spray width and selects the cooling mode at the end (112), preferably the thermal model pre-conditions the hydraulic system supplying the ramps (30) and (40), then at each pass the thermal model compares the calculated or measured temperature of the blank (11) with the desired temperature, the thermal model controls the gate valves (49) of the nozzles (35) and (45) depending on the position of the blank (11), preferably the thermal model manages the top nozzle (35) and the bottom nozzle (45) differently.

[0097] Preferably, the principle of control of the cooling system is as diagrammed in FIG. 16. A thermal model or automaton coded on a computer calculates the spray width corresponding to the width of the blank. Preferably, the spray width excludes the edge (111) to minimize cooling of the edge (111) as much as possible to reduce defects such as edge cracks. The thermal model selects the cooling mode at the end (112). Preferably, no spraying is performed on the end (112) to minimize cooling of the end (112) as much as possible to facilitate engagement in the hot rolling mill and reduce the alligator cracking phenomenon. Preferably, the model defines a pre-adjustment of the hydraulic system to supply the ramps (30) and (40) so that the cooling fluid jets (36) and (46) are rapidly established immediately after the gate valve (49) opens. Then, at each pass, the thermal model compares the calculated or measured temperature of the blank (11) with the desired temperature. The measured temperature can be obtained by, for example, measuring the surface temperature using non-contact infrared pyrometry or by contact measurement on the surface of the blank (11). The calculated temperature can be related to the surface temperature or the average temperature. For example, the calculated temperature can be calculated using thermal simulation software such as MSC Marc. By comparing the desired temperature with the temperature of the blank (11), the thermal model controls the gate valves (49) of the nozzles (35) and (45) using the position and dimensions of the blank (11). The position of the blank (11) can be calculated or measured. If the blank (11) is not present between the upper and lower units of the cooling system, the nozzles (35) and (45) are not replenished to avoid, for example, the jet (46) of the lower nozzle (45) from dissipating onto the upper roll (21) or the jet (36) of the upper nozzle (36) from dissipating onto the lower roll (22). The maximum non-uniformity of the surface temperature of the blank (11), preferably excluding the edges (111) and / or ends (112) of the blank (11) after release from the holding section of the rolling mill and cooling device, may be less than 20°C, preferably less than 10°C.Preferably, the thermal model manages the upper nozzle 35 and the lower nozzle 45 differently to avoid the formation of bridges or boats in the blank 11. Preferably, the absolute value of the temperature difference between the upper and lower surfaces of the blank 11 is less than 10°C, more preferably less than 7°C, more preferably less than 5°C, and more preferably less than 2°C. More preferably, the temperature of the upper surface of the blank 11 is substantially equal to the temperature of the lower surface of the blank 11.

[0098] The maximum level of inhomogeneity and the desired temperature of the blank (11) with or without the edges (111) and / or ends (112) are metallurgical choices that depend on the product to be produced. Preferably, the control of the cooling system is integrated into the control system of the reversing hot rolling mill, which controls the rolling parameters.

[0099] Preferably, the thermal device does not cool the surface of the blank (11) below the Leidenfrost temperature of the cooling fluid. The Leidenfrost temperature is the temperature above which the cooling fluid forms a vapor film. The Leidenfrost temperature of the cooling fluid sprayed onto the blank depends on the properties of the cooling fluid and its surface flow rate. This temperature value is typically around 300°C for typical cooling fluids, emulsions, and rolling oils and additives, which is lower than the usual temperatures for hot rolling on a reversing mill. The cooling system can induce strong temperature inhomogeneities between the surface and core of the blank (11). It is believed that spraying the blank (11) for an excessively long time or too intensively can cause the surface temperature of the blank (11) to momentarily drop below the Leidenfrost temperature, which significantly increases the risk of losing thermal control over the uniformity and average value of the blank (11) thus cooled. Thus, in each pass, the thermal model monitors that the scattering envisaged in the subsequent pass does not risk generating a blank temperature lower than the Leidenfrost temperature.

[0100] Preferably, the typical average cooling rate V of the blank 11 during its passage between the upper convex envelope 52 and the lower convex envelope 62 is approximately V = C / e, where V is in °C / s, e is the blank thickness in mm, and C is a constant between 400 and 1000 °C / s x mm, preferably between 600 and 900 °C / s x mm, and more preferably between 700 and 800 °C / s x mm. The formula V = C / e is specifically an approximation that requires the surface of the blank 11 to remain above the Leidenfrost temperature. The drop in average temperature DT, in °C, of ​​the blank 11 after passing through the upper convex envelope 52 and the lower convex envelope 62 of the cooling system is typically approximately DT = C / e x d, where d is the duration of the passage of a point of the blank 11 between the convex envelopes, and the speed of the blank 11 is constant. This formula is in particular an approximation that requires that the surface of the blank (11) remain above the Leidenfrost temperature. Preferably, the thickness range of the blank (11) for application of said formula is a minimum of 25 mm, preferably 50, preferably 75 mm, preferably 100 mm, preferably 110 mm, and a maximum of 200 mm, preferably 175 mm, preferably 150 mm, preferably 140 mm, preferably 130 mm, preferably 125 mm, preferably 120 mm.

[0101] In a preferred embodiment, the cycle time for hot rolling AA6xxx alloy, preferably AA6016 alloy, blanks (11) is reduced by at least 30 seconds, preferably at least 60 seconds, more preferably at least 90 seconds using the method according to the invention compared to rolling without the method. In a preferred embodiment, the cycle time for hot rolling AA5182 alloy blanks (11) is reduced by at least 15 seconds, preferably 20 seconds, more preferably 45 seconds compared to rolling without the method. The cycle time is the duration between the start of the first pass and the end of the last pass of hot rolling using the reversing hot rolling mill of the invention.

[0102] In another preferred embodiment, the cooling system is used, preferably only once, to reduce the average temperature of the blank by at least 50°C up to an average temperature of more than 400°C in less than 10 seconds, preferably less than 8 seconds, for a blank (11) of at most 114 mm thickness.

[0103] In one embodiment, the cooling system allows for the temperature of the blank (11) to be controlled over a predefined thermal path during hot rolling. The thermal path is the progression of the temperature of the blank (11) over the duration of hot rolling. The thermal path is a metallurgical choice that is driven by the alloy, the desired properties of the finished product, and the capabilities of the hot rolling mill.

[0104] In a preferred embodiment, the cooling system makes it possible to control the blank (11) on an isothermal thermal path. A thermal path is isothermal if the temperature of the blank (11) during hot rolling does not vary by ±10°C compared to the temperature of the plate just before the start of hot rolling. Preferably, the temperature of the blank (11) is substantially equal to the temperature of the plate before the start of hot rolling.

[0105] In a first embodiment illustrated by FIG. 6, for each cooling system, the upper convex envelope (52) and the lower convex envelope (62) are located near the rolls of the rolling mill, and preferably the maximum distances D55 and D65 from the convex envelopes (52 and 62) to the rolls (21 and 22) along the direction S are less than three times the diameter of the largest of the work rolls (21 and 22), and / or the lengths D56 and D66 of the convex envelopes (52, 62) along the direction S are less than the diameter of the largest of the work rolls (21) or (22). Preferably, the convex envelopes (52, 62) are substantially opposite each other. This embodiment is advantageous because it allows the blank (11) to be cooled immediately upon leaving the holding section of the rolls (21) and (22). This is highly advantageous because the speed of a reversing hot rolling mill is often limited to avoid overheating the blank 11, which would lead to burning or even breaking the blank 11. This is highly advantageous because it improves the productivity of the hot rolling mill. In fact, the speed of a reversing hot rolling mill is often limited to avoid overheating the blank 11, which would lead to burning or even breaking the blank 11.

[0106] In this first embodiment, there is preferably a second cooling system on another side of the reversing hot rolling mill, a non-limiting example of which is shown in Figure 7. The second cooling system is preferably symmetrical to the first cooling system with respect to a plane passing through the axes of the work rolls (21) and (22). This arrangement is advantageous because it allows the blank (11) to be cooled in the same way in each rolling pass, both before entering the holding section of the reversing mill and immediately upon exiting this holding section.

[0107] This system is advantageous because it allows for better control of the temperature of the blank at each pass during reverse rolling of the blank, which is beneficial to both the metallurgical quality of the product and the productivity of the reversing mill.

[0108] Another non-limiting example of the first embodiment is provided by FIGS.

[0109] In a first preferred embodiment, the cycle time of hot rolling of the blank (11) is reduced by at least 30 seconds for AA6xxx alloys, preferably 60 seconds, more preferably 90 seconds for AA6016 alloys.

[0110] In a first preferred embodiment, the cycle time of hot rolling of the blank (11) is preferably reduced by at least 15 seconds, preferably 20 seconds, more preferably 45 seconds for the AA5182 alloy.

[0111] The second embodiment is a cooling system that allows for rapid cooling of the blank (11) during hot rolling.

[0112] This embodiment is designed to spray each point of the blank 11 for 10 seconds, preferably 8 seconds. Those skilled in the art will be able to adapt the following characteristics to their particular rolling mill and blank 11 speed.

[0113] In one preferred embodiment of the second preferred embodiment, illustrated but not limited to in FIG. 13, the upper cooling device comprises at least one pair of inclined portions (303 and 304) of the nozzles (353, 354), preferably three pairs of inclined portions (303 and 304), in each pair of inclined portions (303 and 304), the cooling fluid jets (363, 364) are directed oppositely, the difference β-α / 2 is positive or zero, preferably zero, the surfaces (513, 514) of the blank (11) diffused by the jets (363, 364) preferably overlap at a ratio of 1 / 3 to 2 / 3, preferably 1 / 2, and the lower cooling device comprises at least one inclined portion (40) of the nozzles (45), preferably eight inclined portions (40), the cooling fluid jets (46) of which are conical and have axes substantially perpendicular to the blank (11). The angle β is the angle between the axes of the nozzles (353, 354) and a line V perpendicular to the top surface of the blank (11). The angle α is the angle of the cone of the cooling fluid jet generated by the nozzle. These angles are diagrammed in FIG. 5a along with the inclined portion (30), nozzle (35), and jet (36). This configuration is advantageous because it concentrates the cooling fluid within at least a portion of the overlapping area of ​​the jet (36), thereby discharging the cooling fluid at a sufficient velocity on the periphery of the blank (11) to prevent it from flowing out toward the end, thereby enabling uniform cooling of the entire length of the blank. This system also reduces the energy consumption of the cooling fluid discharge device (38) and even makes it possible to eliminate these devices.

[0114] In another embodiment of the second preferred embodiment, illustrated but not limited to, by Figures 12 and 14, the upper cooling device includes at least one inclined section (30) of the nozzle (35), preferably six inclined sections (30), and the lower cooling device includes at least one inclined section (45), preferably eight inclined sections (40), all of which generate conical cooling fluid jets (36) and (46), the axes of which are substantially normal to the blank (11), and the cone angle α of the jets (36) is less than 20°, preferably substantially 15°. This device has the advantage of being easier to manufacture. The angle α of the conical jets, less than 20°, preferably substantially 15°, limits the horizontal component of the velocity of the cooling fluid upon impact on the blank (11), thereby limiting the outflow of the cooling fluid on the blank (11) and controlling its cooling.

[0115] In a second preferred embodiment, the cooling system is preferably used only once to reduce the average temperature of the blank (11) by at least 50°C up to an average temperature of more than 400°C in less than 10 seconds, preferably less than 8 seconds, for a blank (11) of at most 114 mm thickness, as shown in Figure 19.

[0116] In another embodiment, the blank (11) can be further cooled, for example by passing it under a cooling system twice.

[0117] In another embodiment, thicker blanks can be cooled by 50° C. by slowing the passing speed of the blank (11) or increasing the length of the surfaces (51) and (61) receiving the dissipation. As a non-limiting example, as shown in FIG. 20, a 140 mm blank (11) can be cooled by 50° C. in at least 15 seconds, preferably at least 10 seconds.

[0118] In another embodiment, a typical average cooling rate V of the blank 11's average temperature during its passage between the upper convex envelope 52 and the lower convex envelope 62 is approximately V = C / e, where V is in °C / s, e is the blank's thickness in mm, and C is a constant between 400 and 1000, preferably between 600 and 900, and more preferably between 700 and 800. The formula V = C / e is specifically an approximation that requires the blank 11's surface to remain above the Leidenfrost temperature. The drop in the blank 11's average temperature DT, in °C, after its passage through the upper convex envelope 52 and the lower convex envelope 62 of the cooling system is typically approximately DT = C / e × d, where d is the duration of the passage of a point of the blank 11 between the convex envelopes, and the blank 11's velocity is constant. This formula is in particular an approximation that requires that the surface of the blank (11) remain above the Leidenfrost temperature. Preferably, the thickness range of the blank (11) for application of said formula is a minimum of 25 mm, preferably 50, preferably 75 mm, preferably 100 mm, preferably 110 mm, and a maximum of 200 mm, preferably 175 mm, preferably 150 mm, preferably 140 mm, preferably 130 mm, preferably 125 mm, preferably 120 mm.

[0119] A third preferred embodiment is a method for rolling an AA6xxx series aluminum alloy, comprising: a. Casting of rolled plates made of AA6xxx alloys; b. A homogenization step of the rolled plate, optionally followed by a reheating step; c. a first hot rolling step for converting the rolled plate into a blank having a first exit thickness based on a first temperature at the start of the hot rolling; d. cooling the blank thus obtained from its average temperature to the second temperature at the start of the second hot rolling at a typical average cooling rate of approximately V=C / e, where V is in °C / s, e is the thickness of the blank in mm, and C is a constant between 400 and 1000 °C / s x mm, preferably between 600 and 900 °C / s x mm, more preferably between 700 and 800 °C / s x mm; e. a second hot rolling step for converting the thus cooled blank into a strip of final hot rolled thickness under deformation and temperature conditions such that the strip recrystallizes to at least 50%; f. cold rolling the strip into sheet; The rolling method includes:

[0120] The first hot rolling and cooling are preferably carried out using a reverse hot rolling mill according to the invention. During the cooling of step d, the cooling system is preferably used only once to reduce the average temperature by at least 50°C at a typical average cooling rate of the average temperature of the blank, down to an average temperature of more than 400°C. Preferably, the thickness range of the blank during this cooling is a minimum of 25 mm, preferably 50, preferably 75 mm, preferably 100 mm, preferably 110 mm, and a maximum of 200 mm, preferably 175 mm, preferably 150 mm, preferably 140 mm, preferably 130 mm, preferably 125 mm, preferably 120 mm.

[0121] In one embodiment of the third preferred embodiment, during cooling step d, the cooling system is preferably used only once to reduce the average temperature of the blank by at least 50°C up to an average temperature of more than 400°C within 10 seconds, preferably within 8 seconds for a blank (11) with a thickness of at most 114 mm.

[0122] The inventors have surprisingly discovered that this method makes it possible to improve productivity while maintaining mechanical, surface quality and corrosion resistance properties at least equal to those obtained without the method according to the invention. These products may be particularly useful in the automotive industry for manufacturing external body parts.

[0123] In a third preferred embodiment, among the AA6xxx series alloys, preferred alloys are AA6005, AA6009, AA6013, AA6014, AA6016, AA6022, AA6056, AA6061, AA6111, AA6181, AA6216, AA6316, AA6451, AA6501, AA6502, AA6603, AA6605, AA6607.

[0124] In one embodiment of the third preferred embodiment, the composition of the AA6xxx series alloy plate is, in weight %: 0.5-0.8 Si; 0.3-0.8 Mg; max. 0.3 Cu; max. 0.3 Mn; max. 0.5 Fe; max. 0.15 Ti; balance aluminum and unavoidable impurities each max. 0.05, total not exceeding 0.15, and preferably an alloy containing 0.6-0.75 Si; 0.5-0.6 Mg; max. 0.1 Cu; max. 0.1 Mn; 0.1-0.25 Fe; max. 0.05 Ti; balance aluminum and unavoidable impurities each max. 0.05, total not exceeding 0.15.

[0125] In another embodiment of the third preferred embodiment, the composition of the AA6xxx series alloy plate is, in weight %: 0.7-1.3 Si; 0.1-0.8 Mg; max. 0.3 Cu; max. 0.3 Mn; max. 0.5 Fe; max. 0.15 Ti; balance Aluminium and unavoidable impurities each max. 0.05, total not exceeding 0.15, and preferably 0.8-1.1 Si; 0.2-0.6 Mg; max. 0.1 Cu; max. 0.2 Mn; 0.1-0.4 Fe; max. 0.1 Ti; balance Aluminium and unavoidable impurities each max. 0.05, total not exceeding 0.15.

[0126] After casting, the plate is preferably homogenized at a temperature of 500-570°C, preferably 540-560°C, typically for a duration of at least 4 hours and preferably for at least 8 hours. In a preferred embodiment, the maximum temperature of homogenization is at most 555°C. Homogenization can be carried out in a single step or in multiple steps, with increasing temperatures to reduce the risk of combustion.

[0127] In a third preferred embodiment, the plate is then rolled into a blank during a first hot rolling run on a reversing mill. The starting rolling temperature of the first hot rolling run is preferably above 470°C, more preferably above 490°C, and even more preferably above 500°C. Preferably, during this first hot rolling run, the temperature is maintained above 450°C, preferably above 470°C, and more preferably above 490°C. Preferably, the first exit gauge is between 90mm and 140mm, preferably between 100mm and 130mm, and more preferably between 110mm and 120mm.

[0128] This thickness of the blank is extremely advantageous in plants whose hot rolling train consists successively of two reversing hot rolling mills and optionally of one hot tandem rolling mill: in fact, this thickness of the blank corresponds to the thickness of the blank during its transfer between the first reversing rolling mill and the second reversing rolling mill, and cooling can then be carried out without any time loss.

[0129] The blank is then cooled from its average temperature to the second temperature at the start of the second hot rolling at a cooling rate of at least 5°C / s. Advantageously, the first hot rolling and cooling are carried out using a reverse hot rolling mill according to the invention, as illustrated in particular by Figures 12 to 15.

[0130] After cooling, the blank is rolled into a strip by a second hot rolling. The second hot rolling can be carried out continuously on multiple hot rolling mills, for example, a second reversing hot rolling mill followed by a tandem rolling mill, or the reversing hot rolling mill used for the first hot rolling followed by a tandem rolling mill. Preferably, the starting temperature of the second hot rolling is 380 to 450°C, more preferably 400 to 440°C, and even more preferably 420 to 435°C. The strip is rolled to the final hot rolling thickness under conditions such that the cooled strip is at least 50%, preferably at least 80%, more preferably at least 90%, and particularly preferably at least 98% recrystallized. By at least 50%, 80%, 90%, and 98% recrystallization, respectively, is meant that the recrystallization percentage measured through the thickness and at least three points across the width is at least 50%, 80%, 90%, and 98%, respectively. Typically, recrystallization varies through the thickness, being complete at the surface and incomplete in the middle thickness. The preferred recrystallization percentage depends on the alloy of the strip.

[0131] To obtain said recrystallization, it is advantageous for the exit temperature of the second hot rolling to be at least 345°C, preferably at least 350°C and more preferably at least 355°C. The thickness reduction during the last pass of the second hot rolling is one parameter for ensuring recrystallization. The reduction during the last pass of the second hot rolling is at least 25%, preferably at least 30%, preferably 40% and more preferably at least 45%. The typical thickness of the strip obtained in the second hot rolling is 4 to 10 mm.

[0132] The strip is then cold-rolled into a sheet. According to the method of the present invention, annealing and / or solution treatment between or during hot and cold rolling is not required to obtain the desired mechanical, formability, surface condition, or corrosion properties. Preferably, no annealing and / or solution treatment is performed between or during hot and cold rolling. The sheet typically has a thickness of 0.5 to 2 mm. In a preferred embodiment, the cold rolling reduction is 70% to 80%. In another preferred embodiment, the reduction between the strip and the sheet is at least 80% to obtain the most favorable surface quality.

[0133] Preferably, after step f, a complementary step is carried out: g. solution treating and quenching the sheet thus obtained in a continuous heat treatment furnace; can be implemented.

[0134] The continuous heat treatment furnace is preferably adapted to perform an equivalent holding time at 560°C.

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[0135] Preferably, after solution treatment and quenching, and optionally pre-aging, the sheet is aged at ambient temperature to reach the metallurgical temper T4, cut and shaped to its final shape, painted, and bake-hardened.

[0136] Thin plate is held at 560℃ for an equivalent duration

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[0137] Cold-rolled sheet is extremely advantageous, if only because it can be easily processed by solution treatment. Conventional operations aimed at obtaining a good surface condition compatible with the quality for exterior body sheet generally involve supplemental heat treatments between successive processing steps, compared to the sheet obtained according to the present invention. The presence of this supplemental heat treatment requires the skilled person to use high temperatures and long equivalent hold durations on the solution treatment line with successive annealings to obtain sufficiently high mechanical strength in the as-received metallurgical temper and with post-baking of paint. In contrast, the cold-rolled sheet of the present invention requires only an equivalent hold duration at 560°C.

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[0138] Typically, continuous annealing lines operate in such a way that the heating rate of the sheet is at least 10°C / s for metal temperatures below 400°C, the time spent above 530°C is between 15 and 90 seconds, and the quenching rate is at least 10°C / s, preferably at least 15°C / s, for thicknesses of 0.9 to 1.1 mm. The solution treatment brings the metal to a temperature below but close to the solidus temperature, i.e., generally above 530°C and below 570°C. The coiling temperature after solution treatment is preferably between 50°C and 90°C, preferably between 60°C and 80°C.

[0139] After solution treatment and quenching, the sheet may be aged to reach a metallurgical temper of T4, then cut and shaped to the final geometry, painted, and baked to harden.

[0140] The method of the present invention is extremely useful for the production of sheet metal for the automotive industry, which combines high tensile elastic limit and formability suitable for cold pressing operations, as well as excellent surface quality on parts and high corrosion resistance with high productivity.

[0141] In a fourth preferred embodiment, the hot rolling mill combines the first preferred embodiment and the second embodiment.

[0142] One non-limiting example is shown in Figure 15. The hot rolling mill is surrounded by a cooling system that allows its productivity to be improved. A third cooling system allows for fast cooling during transfer towards the subsequent part of the hot rolling. This fourth embodiment allows for an increase in productivity on the reversing hot rolling mill, fast cooling without affecting productivity during transfer towards the subsequent part of the rolling, all together allowing for the delivery of AA6xxx alloy plate with excellent surface quality while improving the productivity of the solution treatment and quenching line.

[0143] Example 1: The reverse hot rolling mill according to the present invention, as illustrated in FIG. 7, includes two cooling systems symmetrically installed on both sides of the work rolls. Each of these two cooling systems consists of an upper cooling device and a lower cooling device. The upper cooling device includes a sloped nozzle (35) (30) directed toward the roll (21). Each sloped nozzle is protected by a protective element (37). The lower cooling device includes two sloped nozzles (40) (45) installed below the plane of the axes of the rollers (23): a first sloped nozzle (40) between the first and second rollers (23) from the roll (22) and a second sloped nozzle (45) between the second and third rollers (23). The rollers (23) are sufficiently close together that the installation of the protective element (47) is not necessary. The nozzles (35) and (45) produce a solid conical jet of spray. Nozzle (45) produces a conical jet that is approximately tangential to roller (23). Nozzles (35) and (45) are fed by fast response gate valves with a response time of 0.2 seconds. The convex envelope of the upper diffused surface is substantially opposite the convex envelope of the lower diffused surface. The convex envelope is located at less than three times the diameter of the largest of the two work rolls of the reversing hot rolling mill. The average surface flow rate per surface is approximately 1200 l / min / m. 2 The quench fluid is a rolling mill emulsion that serves to lubricate the blank 11 during hot rolling of the blank. The quench fluid is in a vapor film forming state on the surface of the blank 11.

[0144] In each hot rolling pass, a 500 mm thick plate was hot rolled with cooling according to the present invention. Figure 18 shows the temperature field at the top surface of an AA6016 alloy blank, 2000 mm wide, 50 mm thick and 5000 mm long, immediately after the last pass of reverse hot rolling. The surface temperature inhomogeneity of the blank, including the edges and ends, is 10°C both in length and width.

[0145] An identical plate of the same alloy was hot rolled in the same manner, but without the use of the cooling system of the present invention. Figure 17 shows the temperature field at the top surface of the resulting blank, of the same dimensions as presented in Figure 18, immediately after the last pass of reverse hot rolling. The surface temperature inhomogeneity at the surface of the blank is 25°C in both length and width without the use of the cooling system of the present invention.

[0146] Cooling the blank during rolling design allows for a 90 second reduction in reverse hot rolling cycle time, in addition to a significant improvement in blank thermal uniformity using the present invention over practice without the present invention.

[0147] Two plates made of AA5182 alloy, 1480 mm wide and 510 mm thick, were hot rolled, one with the present invention and the second without, with the hot rolling cycle time for the first plate being 64 seconds shorter than that of the second.

[0148] Example 2: A hot rolling mill according to the present invention, including work rolls (21, 22) and a cooling system with six upper inclined nozzles (30) and eight lower inclined nozzles (40), is shown in FIG. 14. It is part of a hot train that includes a second reversing mill with work rolls (25, 26). These two reversing hot rolling mills are part of a hot train that further includes a hot tandem mill. The upper inclined nozzles (35) are oriented perpendicular to the plane of the blank (11). The upper nozzle (36) jet is solid conical, with a cone angle of substantially 15°. The cooling fluid is an emulsion that serves to lubricate the work rolls during hot rolling. The lower inclined nozzles (45) are oriented perpendicular to the lower surface of the blank (11). The jet of the bottom nozzle is a solid cone with a cone angle of substantially 90.degree.. The surfaces (52) and (62) receiving the diffusion are substantially opposite each other.

[0149] The system is capable of cooling a 114 mm thick sheet from a temperature of 470°C to an average temperature of 420°C in 8 seconds, as shown in the graph of Figure 19, obtained by digital simulation. After 20 seconds of cooling, the thickness inhomogeneity of the blank is approximately 9°C, and after 30 seconds of cooling, the thickness inhomogeneity of the blank is approximately 2°C. In Table 1, examples D and E, 114 and 109 mm blanks made of AA6xxx alloys, were cooled using a system without any special adjustments to have hotter edges or ends. The temperatures listed in Table 1 are measurements made on the surface of the blank. Given the transfer times of over 30 seconds between the first reversing hot rolling mill and the cooling system, and between the cooling system and the second reversing hot rolling mill, the surface temperatures of blanks D and E represent the average temperature of the blank as well as the temperature at the core. Thus, sheets D and E were cooled by 57 and 75°C, respectively.

[0150] [Table 1]

[0151] Five plates were cast, the composition of which is given in weight percent in Table 1. Table 1 also details the processing method. Columns A and B describe the plate and its processing steps into a blank, then strip, then sheet for producing an internal body element with no requirements in terms of surface quality. Column C describes the plate and its typical processing steps into a blank, then strip, then sheet for producing an external body element with important requirements in terms of surface quality. This is a reference example with no cooling during hot rolling. Columns D and E are examples of the invention.

[0152] Five plates A, B, C, D, and E were homogenized according to the conditions listed in Table 1. Plates A, B, D, and E were transported to the first reverse hot rolling mill. Plate C was cooled to ambient temperature, then reheated to the starting temperature of the first hot rolling mill, and transported to the first reverse hot rolling mill. The five plates were rolled to 114 mm thick blanks in the first hot rolling mill, except for plate E, which was rolled to a 109 mm thick blank. The five blanks then passed through the cooling system of the first hot rolling mill and transported to the second reverse hot rolling mill. Blanks A, B, and C passed through the cooling system without spraying and were only naturally cooled by air during their transport to the second reverse hot rolling mill. Blanks D and E passed through the operating cooling system and were thus cooled to the surface temperatures listed in Table 1. The five blanks were then rolled in a second reversing hot mill and then rolled into strip using a tandem hot mill. Upon exiting the tandem hot mill, the strip was coiled according to the properties in Table 1. After cooling, the five coilers were cold rolled into sheet.

[0153] After the final hot rolling pass and before coiling, samples of strips C, D, and E were taken. These samples were rapidly cooled by immersing them in a water tank at ambient temperature. Recrystallization rate tests were then performed by heating each sample to different temperatures in the laboratory, followed by cooling the samples in a manner similar to the cooling of a coiler after hot rolling. Metallography was then performed (Figure 25) and the recrystallization rate was evaluated (Table 2).

[0154] [Table 2]

[0155] The quality of the roping-like surface state was characterized for sheets A, B, D and E. The roping was measured in the following way: a sample of approximately 270 mm (transverse to the rolling direction) x 50 mm (in the rolling direction) was cut in the sheet. A preliminary deformation of 15% tension was then applied perpendicular to the rolling direction, i.e. in the length direction of the sample. The sample was then subjected to the action of a P800 type coated abrasive to reveal the roping.

[0156] Sheets D and E produced according to the invention have a surface quality adapted for producing exterior body elements, as shown in Figure 23 for sheet D and in Figure 24 for sheet E. This is not the case for sheets A and B, as shown in Figure 21 for sheet A and in Figure 22 for sheet B. The cooling system demonstrates its usefulness for obtaining surface quality using a more economical method that eliminates reheating, as in the case of sheet C, which serves to produce exterior body elements and is not specifically characterized for surface quality.

[0157] The following characterization was performed to evaluate the kinetics of the solution treatment of the three sheets C, D, and E. For the three sheets C, D, and E, specimens were taken after cold rolling to final gauge. First, various solution heat treatments were performed on the specimens by varying the time for which the specimens were solution treated in a fluidized bed furnace at 570°C. A long soak time of 90 seconds at 570°C was used to fully solution treat the specimens. The duration of 90 seconds at 570°C is calculated using the formula

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[0158] To obtain a solution treatment with incomplete dissolution of the alloy, a shorter solution treatment duration was used in a fluidized bed furnace at 570°C. All of these solution heat treatments were followed by a water quench down to 80°C and a pre-aging treatment at 80°C for 8 hours. After these different heat treatments of solution treatment, subsequent quenching, and subsequent pre-aging, the specimens were aged in an oil bath at 205°C for 2 hours to reach the metallurgical temper T6.

[0159] Tensile tests were then carried out. The elastic limit (Rp 0.2) obtained after final ageing in metallurgical temper T6 was used as an indicator of the solution-treated quality of the specimens. In fact, depending on the precipitation state present in the sheet, the duration of the solution-treated treatment at the solution-treated temperature (here 570 °C) required to dissolve these precipitates varies. For reasons of productivity on the production machines that carry out the solution-treated treatment, it is advantageous to keep the solution-treated treatment duration as short as possible.

[0160] The results of the tensile tests of the three sheets C, D and E are displayed in Table 3 and in Figure 26. On this graph, each measured elastic limit (T6YS) is normalized with the elastic limit (T6YSmax) obtained for the same sheet after a solution treatment time of 90 seconds in a fluidized bed at 570°C.

[0161] 26 shows that the solution treatment reaction rate of the two sheets D and E according to the invention is much faster than that of Comparative Example C. Indeed, after 50 seconds of immersion in the fluidized bed at 570°C, the elastic limits of the temper T6 of Examples D and E according to the invention reach more than 99% of the maximum elastic limit of the temper T6, while Comparative Example C is only at more than 98% of the maximum elastic limit of the temper T6. Similarly, after 30 seconds of solution treatment in the fluidized bed at 570°C, the elastic limits of the temper T6 of Examples D and E according to the invention reach more than 98% of the maximum elastic limit of the temper T6, while Comparative Example C is at 96% of the maximum elastic limit of the temper T6. Thus, the present invention further makes it possible to accelerate the productivity of the solution treatment.

[0162] [Table 3] [Explanation of symbols]

[0163] 11 Blank 21 Upper work roll 22 Lower work roll 23 Laura 30 Slope 35 nozzles 36 Cooling fluid jet 40 Slope 45 nozzles 46 Cooling fluid jet

Claims

1. A method for rolling an AA6xxx series aluminum alloy, comprising: a. Casting a rolled plate made of an AA6xxx series alloy; b. A homogenization step of the rolled plate, optionally followed by a reheating step; c. a first hot rolling step for converting the rolled plate into a blank having a first exit thickness based on a first temperature at the start of hot rolling; d. Cooling the blank thus obtained at an average cooling rate of V=C / e from the average temperature of the blank to the second temperature at the start of the second hot rolling, where V is in °C / s, e is the thickness of the blank in mm, and C is a constant between 400 and 1000 °C / s x mm; e. A second hot rolling step for converting the thus cooled blank into a strip of final hot rolled thickness under deformation and temperature conditions such that the strip recrystallizes to at least 50%; f. cold rolling the strip into a sheet; A rolling method comprising:

2. 2. The method according to claim 1, wherein the constant C is 600 to 900° C. / s×mm.

3. 2. The method according to claim 1, wherein the constant C is 700 to 800° C. / s×mm.

4. 4. The method according to claim 1, wherein during the cooling step d a cooling system is used to reduce the average temperature of the blank by at least 50°C, up to an average temperature of more than 400°C.

5. 5. The method according to claim 4, characterized in that the cooling system is used only once to reduce the average temperature of the blank by at least 50°C up to an average temperature of more than 400°C.

6. 6. The method according to any one of claims 1 to 5, characterized in that the temperature during the first hot rolling is maintained above 450°C, and / or the first exit gauge is between 90mm and 140mm, and / or the exit temperature of the second hot rolling is at least 345°C, and / or the reduction in the last pass of the second hot rolling is at least 25%, and / or the reduction in the cold rolling is between 70% and 80% or more than 80%.

7. 7. The method according to any one of claims 1 to 6, characterized in that the temperature during the first hot rolling is maintained above 470°C, and / or the first exit thickness is 100-130mm, and / or the exit temperature of the second hot rolling is at least 350°C, and / or the reduction of the last pass of the second hot rolling is at least 30%.

8. 7. The method according to any one of claims 1 to 6, characterized in that the temperature during the first hot rolling is maintained above 490°C, and / or the first exit gauge is between 110mm and 120mm, and / or the exit temperature of the second hot rolling is at least 355°C, and / or the reduction of the last pass of the second hot rolling is at least 40%.

9. 9. The method according to any one of claims 1 to 8, characterized in that the reduction in the last pass of the second hot rolling is at least 45%.

10. After step f, a complementary step is performed: g. Solution treating and quenching the sheet thus obtained in a continuous heat treatment furnace, the continuous heat treatment furnace being at 560°C for an equivalent holding time. [Equation 1] is less than 30 seconds, and this equivalent hold duration is given by the formula [Equation 2] is calculated using Q is the activation energy of 200 kJ / mol and R = 8.314 J / mol / K; 10. The method according to claim 1, wherein the following is carried out:

11. Equivalent holding time at 560°C [Equation 3] 11. The method of claim 10, wherein the time is less than 25 seconds.

12. Equivalent holding time at 560°C [Equation 4] 11. The method of claim 10, wherein the time is less than 20 seconds.

13. 13. A method according to any one of claims 10 to 12, characterized in that after solution treatment and quenching, the sheet is aged at ambient temperature so as to reach the metallurgical temper T4, cut and shaped to obtain its final shape, painted and hardened by baking.

14. 14. The method according to claim 13, characterized in that after solution treatment and quenching, a pre-aging is carried out and the sheet is aged at ambient temperature so as to reach the metallurgical temper T4, cut and shaped to obtain its final shape, painted and hardened by baking.

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