FR3112296A1 - Cooling process and equipment on a hot reversible rolling mill - Google Patents

Abstract

Disclosed is a process for rolling an AA6xxx series aluminum alloy in which a blank is cooled during hot rolling and a thin sheet obtained by this process. The invention makes it possible to improve the productivity of reversible rolling mills by improving the metallurgical quality and/or the productivity of the other transformation stages. The invention is particularly useful in providing superior quality 6xxx alloy sheets for the automotive industry.

Description

Cooling process and equipment on a hot reversible rolling mill

Field of invention

The invention relates to the field of rolling flat aluminum alloy products.

The invention relates to a process implemented by a reversible hot rolling mill equipped with a cooling system which allows better thermal control of aluminum alloy flat products during rolling. The invention also relates to a thin sheet whose method uses cooling during hot rolling which can be obtained by the invention.

State of the art

A hot line for rolling aluminum alloys always includes a reversible rolling mill (that is to say which rolls back and forth) also called a rougher or rougher and, possibly, a multi-stand rolling mill also called a tandem rolling mill , at the exit of which the still hot metal is rolled up. The number of passes and the take-up (thickness reduction per pass) depend on the hardness of the product (its flow stress) and of course, the power of the rolling mill, in terms of torque and effort. Productivity dictates that the greatest possible reductions be taken with each pass. However, we are then limited by the capacity of the rolling mill in terms of rolling force and/or rolling torque, as described for example in the article “Shaping aluminum – Rolling – Patrick Deneuville, © Engineering Techniques – 2010”. During hot processing of aluminum such as hot rolling, the temperature of the metal is always at least typically 200°C.

Hot lines are also known in which two reversible rolling mills follow each other followed by a tandem rolling mill.

Hot reversible rolling mills are often production bottlenecks in factories and given the considerable investments they represent, increasing their productivity is a major issue and obviously we have always thought of increasing the capacity of the rolling mill in terms of stress and/or rolling mill torque.

In the technical state, it has often been considered to improve the productivity of tandem rolling mills rather than that of the reversible rolling mill. The requests below relate in particular to cooling methods or processes installed on finishing hot tandem rolling mills.

Patent application WO201558902 relates to a hot rolling train for aluminum strips and a method for hot rolling an aluminum strip.

This application aims to propose, for a hot rolling train for aluminum strips comprising a tandem finishing rolling train with several stands comprising at least one reel mounted downstream in the direction of rolling and at least one associated cooling section, a solution that makes it possible to better adjust the cooling curves and the temperature-time paths in the product to be rolled during the hot rolling of aluminum strips. For this purpose, the cooling section(s) are arranged in the output zone of the hot rolling train for aluminum strips, and at least one trimming shear installed downstream in the rolling direction is associated with the finishing rolling train tandem.

Patent EP2991783 relates to a process for manufacturing a metal strip. This patent relates to a method for producing a metal strip, in which the strip is rolled in a multi-stand rolling mill, taken out behind the last rolling stand in the transport direction and cooled in a cooling device. To obtain a favorable grain structure and a high degree of flatness, according to the patent, the strip or sheet is subjected directly after passing through the work rolls of the last rolling stand to an additional rapid cooling, strip cooling or sheet still taking place at least partly within the extent of the last rolling stand in the conveying direction, the rapid cooling taking place by applying a cooling fluid from above and below to the strip or sheet, the volume flow of cooling fluid applied from below to the strip or sheet being at least 120% of the volume flow of cooling fluid applied from above onto the strip or sheet.

Patent application WO200889827 relates to a device for cooling a metal strip. This application relates to a device for cooling a metal strip between two rolling mill stands, the strip being guided on an upper guide element of planar design. Below the upper guide element is disposed a spray element which conducts cooling fluid through at least one opening in the upper guide element to the underside of the strip. In order to obtain an improved spray pattern, in accordance with this application, at least two openings juxtaposed in the direction transverse to the direction of advance of the strip are made in the upper guide element and have an elongated shape. The longitudinal axis of the opening is oriented at an angle with respect to the direction of advance of the strip.

There are also processes and equipment to cool the plates before the start of supplying the hot rolling mill.

Patent application WO2016/012691 relates to a cooling process and equipment. This application relates to a process for cooling an aluminum alloy rolling plate, after the heat treatment for metallurgical homogenization of said plate and before its hot rolling, characterized in that the cooling of a value of 30 at 150°C is carried out at a speed of 150 to 500°C/h, with a homogeneity of less than 40°C over the entire treated part of the tray. This application also relates to the installation allowing the implementation of said method as well as said implementation.

Patent application WO 2018/011245 relates to a process for manufacturing a thin sheet of aluminum alloy from the 6xxx series comprising the following steps: casting an aluminum alloy from the 6xxx series to form an ingot ; ingot homogenization; cooling the homogenized ingot at a cooling rate of at least 150°C/h directly to the hot rolling start temperature; hot rolling the ingot to a final thickness and coiling to the final thickness after hot rolling under conditions making it possible to obtain a recrystallization rate of at least 50%; cold rolling to obtain thin cold rolled sheet. The method of the invention is particularly useful for the manufacture of thin sheets intended for the automobile industry which combine a high tensile elastic limit and a formability suitable for cold stamping operations, as well as excellent surface quality and high corrosion resistance with high productivity.

For 6000 series alloys, other modifications are also considered to improve productivity and/or metallurgical properties.

Patent application EP1165851 relates to a process for converting an ingot of a 6000 series aluminum alloy into a self-annealing sheet. This process consists of subjecting the ingot to a two-step homogenization treatment, first at a temperature of at least 560°C, then at a temperature between 450°C and 480°C. This process then consists of hot rolling the homogenized ingot at a starting temperature of between 450°C and 480°C, then at an arrival temperature of between 320°C and 360°C. This results in a hot rolled sheet comprising an exceptionally low Cube recrystallization component.

Patent application US2016/0201158 relates to new processes for increasing productivity on a continuous annealing and re-solution heat treatment line for aluminum sheet products for the automotive industry suitable for treatment thermal with high T4 and post-cure strengths and reduced lineage. By way of non-limiting example, the methods according to the invention can be used in the automotive industry. The heat treatable alloys and methods of the invention can also be applied in the marine, aerospace and transportation industries.

Patent application EP1375691 relates to a 6000 type aluminum alloy laminated sheet containing Si and Mg as main components and possessing excellent formability sufficient to allow flat flap machining, excellent dent resistance, and good hardenability. during the curing of a coating. The alloy sheet has a Lankford coefficient anisotropy greater than 0.4 or a resistance coefficient for texture cube orientations greater than or equal to 20, and has a critical radius of curvature less than or equal to 0.5 mm at 180°C, yielding even when conventional yield strength exceeds 140 MPa by aging at room temperature. Also disclosed is a method for producing the aluminum alloy rolled sheet, which comprises subjecting an ingot to a homogenization treatment, cooling it to a temperature below 350°C at a cooling rate of 100°C / hour or more, optionally down to room temperature, heating it again to a temperature of 300 to 500°C and subjecting it to hot rolling, performing cold rolling of the hot rolled product, and subjecting the cold-rolled sheet to a solution treatment at a temperature greater than or equal to 400°C before carrying out quenching.

Application EP0786535 relates to the homogenization, at a temperature not lower than 500°C, of an aluminum alloy ingot containing not less than 0.4% by weight and less than 1.7% by weight of Si , not less than 0.2% by weight and less than 1.2% by weight of Mg, as well as Al and unavoidable impurities as a balance, then the resulting product is cooled from a temperature not lower than 500°C to a temperature in the range between 350 and 450°C, and the starting point of which allows hot rolling. The hot rolling step being completed at a temperature in the range of 200 to 300°C, the obtained product is subjected to cold rolling at a reduction ratio of not less than 50%, immediately before its processing. in solution. The cold rolled product is then subjected to a solution treatment in which it is kept at a temperature in the range of 500 to 580°C, at a rate of temperature increase of not less than 2°C/s for at most 10 minutes, then the product obtained is subjected to hardening, during which it is cooled to a temperature not higher than 100°C, at a cooling rate not lower than 5°C/s. There is thus obtained a method for producing an aluminum alloy plate for casting, which has high strength and castability, and excellent outward appearance on its post-casting surface, which is suitably used as a material for parts of transportation equipment, such as exterior plates for automobiles.

Patent application JP2015067857 relates to providing an Al-Mg-Si based aluminum alloy sheet for automobile panel excellent in drawability, bendable capable of processing flat bend, shape stability property, coating galling hardening and corrosion resistance, and to provide a manufacturing method therefor, with Al-Mg-Si base aluminum alloy sheet for automotive panel contains Si: 0.4 to 1.5%, Mg: 0.2 to 1.2%, Cu: 0.001 to 1.0%, Zn: 0.5% or less, Ti: 0.1% or less, B: 50 ppm or less, one or more kinds of Mn: 0.30% or less, Cr: 0.20% or less, and Zr: 0.15% or less, and the balance Al with unavoidable impurities. A density distribution of the direction of the cube at a depth part of 1/4 of the thickness of the sheet from a surface is in a range of 10 to 25, an average of the r value r (r = (r + r + r × 2) / 4) is 0.50 or more, an absolute value of an anisotropy index in the plane of the r-value Δr (Δr = (r + rr × 2) / 2) is 0.30 or less and an average crystal particle diameter is 50 μm or less.

For metallurgical or productivity reasons, it may be envisaged to quench the strip after hot rolling.

We know, for example, of a reversible rolling mill followed by a "swimming pool" in which the metal at the final hot thickness is immersed to be cooled ("Shaping aluminum - Rolling - Patrick Deneuville, © Techniques de l' Engineer – 2010”).

Patent application WO2019241514 relates to systems and methods for quenching a metal strip after rolling. This application relates to systems and methods for quenching a metal substrate, comprising cooling a top surface and a bottom surface of the metal substrate until a strip temperature is cooled to an intermediate temperature. The cooling of the upper surface of the metallic substrate is interrupted when the strip temperature reaches the intermediate temperature, and the cooling of the lower surface of the metallic substrate continues until the metallic substrate reaches a target temperature, the target temperature being below the intermediate temperature.

Problem

The problem that the present invention seeks to solve is to improve the productivity of reversible rolling mills without degrading the metallurgical quality of the products obtained, or even by improving the metallurgical quality and/or the productivity of the other processing steps. In particular, there is a demand in the automotive industry for methods with high productivity to provide superior quality 6xxx alloy sheets, particularly in terms of mechanical strength, formability and assembly and appearance of surface after painting.

Object of the invention

A first object of the invention is a process for rolling an aluminum alloy of the AA6xxx series comprising the successive steps of:

1. casting of an alloy rolling plate of the AA6xxx series,
2. homogenization of the rolling plate, optionally followed by reheating,
3. first hot rolling to transform the rolling slab into a blank having a first output thickness from a first hot rolling start temperature,
4. cooling of the blank thus obtained with a typical average cooling rate from the average temperature of the blank of the order of V= C/e down to a 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 value which is between 400 and 1000, preferably between 600 and 900, more preferably between 700 and 800,
5. second hot rolling to transform the blank thus cooled into a strip with the final hot rolling thickness under deformation and temperature conditions such that the strip is recrystallized to at least 50%,
6. cold rolling the strip into a thin sheet.

Another object of the invention is a thin sheet obtained according to the method of the invention, such as after solution treatment in a continuous heat treatment furnace operating in such a way that the holding time equivalent to 560° VS, , is less than 20 s, the equivalent hold time being calculated using the equation

Q being an activation energy of 200 kJ/mol and R = 8.314 J/mol,

it reaches a tensile strength of at least 90% and preferably at least 95% of the maximum tensile strength obtained after solution treatment with a holding time equivalent to 560°C, , of 98s.

Description of figures

: perspective diagram of a blank passing through a rolling mill, the cooling system not being shown.

: top view of a blank passing through a rolling mill, the convex envelope of the surfaces sprayed directly by the jets of cooling fluid during their first impact on the blank being represented.

: view from below of a blank passing through a rolling mill, the convex envelope of the surfaces sprayed directly by the jets of cooling fluid during their first impact on the blank being represented.

: another top view of a blank passing through a rolling mill with the orientation of the jets of cooling fluid, the jets of cooling fluid during their first impact on the blank being represented.

: diagram of nozzles with fast response valves.

: diagram of nozzles with fast response valves.

: diagram in longitudinal section of a rolling mill.

: diagram in longitudinal section of a rolling mill.

: diagram in longitudinal section of a rolling mill.

: diagram in longitudinal section of a rolling mill.

: diagram in longitudinal section of a rolling mill.

: cross-sectional diagram of a rolling mill.

: cross-sectional diagram of a rolling mill.

: diagram in longitudinal section of a rolling mill.

: diagram in longitudinal section of a rolling mill.

: diagram in longitudinal section of a rolling mill.

: a diagram in longitudinal section of a rolling mill.

: diagram of the control principle of the cooling system.

: example of the temperature heterogeneity of the blank for a method according to the prior art.

: example of the temperature heterogeneity of the blank using the method according to the invention according to a preferred embodiment.

: example of the rapid cooling of a 114 mm sheet of AA6XXX aluminum from 470° C. to 420° C. for 8 s with hot rolling emulsion with a method according to the invention according to another preferred embodiment.

: example of the rapid cooling of a 140 mm sheet of AA6XXX aluminum from 470° C. to 420° C. for 10 s with hot rolling emulsion with a method according to the invention according to another preferred embodiment.

: photo of the surface quality in lineage ("roping") without the invention as described in example A.

: photo of the surface quality in lineage ("roping") without the invention as described in example B.

: photo of the surface quality in line ("roping") with the invention as described in example D.

: photo of the surface quality in line ("roping") with the invention as described in example E.

: metallographs showing the rate of recrystallization under different conditions

: graph showing the effect of solution treatment time on a mechanical property

Description of the invention:

All the aluminum alloys referred to below are designated, unless otherwise stated, according to the rules and designations defined by the "Aluminum Association" in the "Registration Record Series" which it publishes regularly.

The metallurgical states in question are designated according to the European standard EN-515.

The static mechanical characteristics in tension are determined by a tensile test according to standard NF EN ISO 6892-1.

The term blank here refers to an intermediate product in aluminum alloy obtained by rolling a rolling plate such as an ingot or a foundry plate, optionally scalped, optionally plated with one or more aluminum alloys, intended for the manufacture a finished product in the form of aluminum alloy strips or sheets, optionally plated with one or more aluminum alloys. A blank is therefore a rolled product whose thickness is intermediate between the rolling plate and the finished product.

Unless otherwise indicated, the term “rolling mill” refers here to a “reversible rolling mill”.

Unlike the prior art in which either the productivity of reversible rolling mills is increased by increasing the capacity of the rolling mill in terms of force and/or rolling torque, or the productivity of the front or rear stages is improved, the present inventors are succeeded in improving the productivity of reversible rolling mills without resorting to these solutions.

The present inventors have in particular observed that, given their hardness, most aluminum alloys tend to heat up too much with each pass. It is then necessary to slow down the rolling mill by taking fewer passes, for example, or leaving a waiting time between each rolling pass.

According to the invention, it has been found that cooling the blank during the hot rolling step makes it possible to improve the productivity of a hot rolling mill or to create new, more economical manufacturing processes by eliminating production steps , while maintaining the same or improved metallurgical quality of the products. Thus, cooling the blank during rolling on reversible rolling mills can also surprisingly give the finished rolled product additional physical properties, such as mechanical properties, surface condition or corrosion resistance.

A reversible hot rolling mill usable for the invention comprises two working rolls, an upper working roll (21) and a lower working roll (22), and at least one cooling system intended to cool a blank (11), said blank (11) moving on rollers (23) and passing through the hot reversible rolling mill between the two working rolls (21) and (22), said cooling system consisting of two cooling devices: a cooling device upper part of the blank (11) and a lower cooling device for the blank (11). The many other parts and systems of the hot rolling mill well known to those skilled in the art, for example non-limiting rolls, motors, columns, extensions, are not shown in the figures.

The upper cooling device comprises at least one ramp (30) of nozzles (35) arranged substantially parallel to the axis of the upper working cylinder (21), the nozzles (35) spraying with jets of cooling fluid (36) the upper face of the blank (11). The lower cooling device comprises at least one ramp (40) of nozzles (45) arranged between the rollers (23) or between the lower working cylinder (22) and the nearest roller (23), substantially parallel to the axis of the lower working cylinder (22), the nozzles (45) spraying with jets of cooling fluid (46) the underside of the blank (11), the axis of the jets of cooling fluid (46) being oriented substantially perpendicular to the lower surface of the blank (11).

There shows a blank (11) passing through a reversible hot rolling mill (the cooling system is not shown in this figure). There shows the edges (111), edges (1111) and ends (112). The blank (11) is represented in a simplified way as a parallelepiped whereas the reality is more complex.

The ends (112) correspond to the part of the blank (11) which engages first or which emerges last from the grip of cylinders (21) and (22). The ends (112) are shown on the simplified as a parallelepiped. Those skilled in the art are familiar with the ends (112) because they will have to be removed to guarantee the manufacture and the quality of the final product. The ends (112) deform in general by rounding and opening in two under the effect of hot rolling, this phenomenon is called "crocodiling" by those skilled in the art. The ends (112) also correspond to the areas of the blank where the rolling is not uniform along the length. The ends (112) can also contain zones corresponding to the transient states of the start or the end of the casting during which the plate was manufactured. The length of the ends (112) depends on the alloys, the rolling and casting conditions and the final applications. This removal of the ends (112) can take place both on a shear installed on the hot train and later in the manufacturing process according to the specific constraints of the final product and its manufacturing process. The length of the ends (112) can typically take the maximum values of 100mm, 200mm, 300mm, 400mm, 500mm or 600mm. The edges (1111) are the faces which connect the upper face of the blank (11) in contact with the upper cylinder (21) and the lower face of the blank (11) in contact with the lower cylinder (22) without be part of the ends (112). The edges (111) are the part of the blank (11) close to the edges (1111) excluding the ends (112). The edges (111) are well known to those skilled in the art because they must be removed to ensure the manufacture and the quality of the finished product. In industrial reality, the edges (111) and edges (1111) have a much more complex shape than that schematized by the because there often appear cracks and folds, well known to those skilled in the art. These deformities must be removed. The edges (111) are not rolled uniformly across the width given the proximity of the edges (1111) and they must be removed in order to guarantee the properties of the final product. This removal of the edges (111) can take place both at the end of hot rolling and later in the manufacturing process according to the specific constraints of the final product and its manufacturing process. The width of the edges (111) can typically take the maximum values of 25mm, 50mm, 50mm, 75mm, 100mm, 125mm, 150mm, 175mm, 200mm or 250mm.

For each cooling system, an upper (52) respectively lower (62) convex envelope is defined as the convex envelope of the surfaces (51) respectively (61) sprayed directly by the jets of cooling fluid (36) respectively (46) during their first impact on the blank (11). An example of a convex envelope (52, 62) of the sprayed surfaces (51, 61) is illustrated by FIGS. 2 and 3 where the cooling system is not shown. Splashing and dripping are not taken into account in the convex hull. A set is convex if for any segment, whose endpoints are in this set, every point of the segment is entirely included in this set. The convex hull of a set is the smallest convex set containing it. The determination of the convex envelopes is carried out by separating the different cooling systems according to their function. There illustrates a non-limiting example comprising a second cooling system. In this example, the convex envelopes of each system are analyzed separately because one system cools the blank (11) before the passage between the cylinders (21) and (22) and the other after the passage between the cylinders (21) and (22). There shows an example with 3 cooling systems, two on either side of the reversible hot rolling mill and a third which is further away and which serves, in the case of this non-limiting example, for rapid cooling before transferring the blank (11) to a second hot rolling mill with its rolls (25) and (26). It will be noted that in the two blanks are shown at two positions although it is possible that these blanks cannot be present simultaneously.

As illustrated by the , for each cooling system, the maximum distance D55 to the cylinder (21) of the convex hull (52) is the maximum of the distance of any point of the convex hull (52) with the line C1 which is the projection of the axis of rotation of the cylinder (21) on the upper surface, of the blank (11), reduced by the radius R1 of the cylinder (21).

As illustrated by the , for each cooling system, the minimum distance D57 from the convex hull (52) to the cylinder (21) is the minimum of the distance from any point of the convex hull (52) with the straight line C1 which is the projection of the axis of rotation of the cylinder (21) on the upper surface, of the blank (11), reduced by the radius R1 of the cylinder (21).

As illustrated by the , for each cooling system, the maximum distance D65 to the cylinder (22) of the convex hull (62) is the maximum of the distance of any point of the convex hull (62) with the straight line C2 which is the projection of the axis of the cylinder (22) on the lower surface of the blank (11), reduced by the radius R2 of the cylinder (22).

As illustrated by the , for each cooling system, the minimum distance D67 from the convex hull (62) to the cylinder (22) is the minimum of the distance from any point of the convex hull (62) with the line C2 which is the projection of the axis of the cylinder (22) on the lower surface of the blank (11), reduced by the radius R2 of the cylinder (22).

For each cooling system, the zone opposite the rolling mill (54) and the zone next to the rolling mill (53) are surfaces which form part of a half-plane which contains the upper convex envelope (52) of the blank ( 11) considered as the simplified parallelepiped of the and which is delimited the line C1.

For each cooling system, as shown in the , the zone opposite the rolling mill (54) is a half-plane which does not contain the convex hull (52) and which is delimited by a straight line E1 which is parallel to the straight line C1 and to the maximum distance D55 added to the radius R1 of cylinder (21) of the right C1.

For each cooling system, the zone next to the rolling mill (53) is delimited by the straight line C1 and by the straight line D1 which is parallel to the straight line C1 and to the minimum distance D57 added to the radius R1 of the cylinder (21) of the right C1.

The direction S is that of the movement of the blank (11).

According to , for each cooling system, the distance D56 in the direction S of the convex envelope (52) is the subtraction of the length D57 from the length D55.

According to , for each cooling system, the distance D66 along the direction S of the convex envelope (62) is the subtraction of the length D67 from the length D65.

In the non-limitatively illustrated embodiment the , the upper cooling device consists of a ramp (30) of nozzles (35) arranged substantially parallel to the axis of the upper working cylinder (21), the nozzles (35) spraying with jets of cooling fluid ( 36) the upper face of the blank (11). The lower cooling device shown in the consists of two ramps (40) of nozzles (45) arranged between the rollers (23), substantially parallel to the axis of the lower working cylinder (22), the nozzles (45) spraying with jets of cooling fluid ( 46) the lower face of the blank (11), the axis of the cooling fluid jets (46) being oriented substantially perpendicular to the lower surface of the blank (11). In one embodiment illustrated by the , the lower cooling device consists of a nozzle ramp (45) located between the lower working cylinder (22) and the closest roller (23).

The embodiments illustrated without limitation, for example by the and the show upper cooling devices consisting respectively of two and three ramps (30) of nozzles (35).

Preferably, the lower nozzles (45) produce jets of cooling fluid (46) which do not directly reach either the rollers (23) or the cylinder (22) in the presence of the blank (11) and which are preferably almost tangent to the rollers (23) and whose distance D67 is preferably greater than a radius of the lower cylinder (22), more preferably than the diameter of the lower cylinder (22) and/or the upper nozzles (35) produce jets of cooling fluid ( 36) which do not directly reach the upper working cylinder (21), preferably the distance D57 is greater than the radius of the upper cylinder (21), more preferably the distance D57 is greater than the diameter of the upper cylinder (21). In one embodiment illustrated by the , the jets of cooling fluid (46) do not directly reach the rollers (23) so that these jets only influence the temperature of the blank (11). In one embodiment illustrated by the , in which the ramp (40) is arranged between the cylinder (22) and a roller (23), the jets of cooling fluid (46) do not directly reach the cylinder (22) so that these jets only influence the temperature of the blank and do not disturb the temperature field of the roll (22) which is an important factor for the quality of the hot rolling. It is advantageous for the distance D67 to be greater than the radius R1 of the lower cylinder (22), preferably the diameter of the lower cylinder (22) to prevent splashes from the jet of fluids (46) from reaching the cylinder (22) and disturbing the cylinder temperature field (22). It is also advantageous that the area of the lower surface of the blank (11) sprayed by the lower jets of cooling fluid (46) is maximized to improve heat exchange. To maximize the surface sprayed by the jets (46) without touching the rollers (23), it is advantageous for the jets (46) to pass flush with said rollers (23) without touching them as illustrated by the These lower jets (46) are therefore preferably almost tangent to the rollers (23). This thus makes it possible to maximize the sprayed surface in order to increase the useful surface for heat exchange. The jets (36) advantageously do not touch the rolls (22) so as not to disturb the temperature field of 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 cylinder (21), preferably for the distance D57 to be greater than the diameter of the upper cylinder (21) to prevent splashes from the jet of fluids (36) from reaching the cylinder. (21) and disturb its temperature field.

Nozzles (24) shown in the and dedicated to the cylinders (21) and (22) can be installed in order to cool or lubricate these organs according to their specific needs independently of the blank (11). In an embodiment not illustrated specific nozzles can be installed to cool the rollers (23). The position of the nozzles (24) on the is only as a principle and is not limiting.

Preferably, the lower nozzles (45) are below the plane passing through the axes of rotation of the rollers (23) located close to said nozzles (45) and/or the lower nozzles (45) are protected by a part (47) having openings for passing the jets of cooling fluid (46) and/or the upper nozzles (35) are protected by a part (37) having openings for passing the jets of cooling fluid (36). Protecting the nozzles (35) and (45) is advantageous because the hot rolling can cause the ends (112) of the blank (11) to open up, which a person skilled in the art calls "crocodiling" and which can strike the nozzles. The blanks (11) can also during hot rolling form bridges or boats, i.e. the blank (11) instead of being substantially flat can bend in the longitudinal direction on leaving the rolling mill, the ends of the blank (11) pointing up or down. Protecting the nozzles (35) and (45) from the blanks (11) is therefore advantageous in order to avoid damaging said nozzles. A non-limiting example of the parts (37) and (47) protecting the nozzles (35) and (45) is illustrated in the , there and the . There is a non-limiting example where only the nozzles (35) are protected by a protective piece (47). When the rollers (23) are very close to each other, installing the nozzles (45) below the plane of the axes of the rollers (23) makes it possible to protect them economically without installing the protective parts (47), as illustrated by figures 6 and 7.

Preferably, each nozzle (35) and (45) is individually supplied by a quick-response valve (49), the response time of which is advantageously less than 1 s, preferably less than 0.5s, and more preferably less than 0.2s . Figures 5a and 5b show non-limiting examples of fast response valves (49) mounted between a ramp (30) respectively (40) and a nozzle (35) respectively (45). Feeding the nozzles individually with fast valves is advantageous because it allows each point of the upper surface and the lower surface of the blank (11) to be cooled in a specific way. These response times make it possible in particular to be able to spray the ends (112) of the blanks (11) with sufficient reliability to adjust their temperature so as to facilitate their engagement between the cylinders (21) and (22). It is then possible to adapt the temperature at the ends (112) of the blank (11) to facilitate its engagement in the reversible hot rolling mill. It is also possible to adapt the temperature on the edges (111) to limit, for example, the phenomena of cracks which reduce the useful width of the blank or which can cause it to break. It is therefore also possible to optimize the temperature of the other parts of the blank (11) according to the properties required on the finished product or according to the properties required for the subsequent stages of production. For example, this is advantageous to better control the properties of the final product such as the anisotropy in the width for products in AA3104 alloy or the uniformity of the mechanical properties of products in AA6xxx alloy. Finally, cooling each point of the blank (11) in a specific way also makes it possible to control the flatness of the blank (11) by controlling the effects of differential expansions.

In one embodiment, the nozzles (35) and (45) are capable of producing jets of cooling fluid (36) and (46) in flat and/or conical and/or cylindrical form. If the shape of the jets is cylindrical, the section of the cylinder is preferably circular. In one embodiment, the nozzles (35) and (45) are capable of producing jets of cooling fluid (36) and (46) by spraying, preferably the nozzles (35) and (45) are capable of producing jets of cooling fluid (36) and (46) by spraying, in the form of a full cone, called conical jets. Conical jets (46) and (36) are a better configuration than flat or cylindrical jets. Indeed, the conical jets allow a better distribution of the cooling fluid on the blank (11). This thus allows a more homogeneous heat exchange and it is thus possible to obtain a blank (11) with for example a temperature heterogeneity of less than 20° C., preferably of less than 10° C.

Preferably, the conical jets of cooling fluid (46) have a cone angle of 90°. This angle can be limited, for example to 60°, by the presence of the rollers (23) so as not to spray them, in particular when the nozzles (45) are below the plane passing through the axes of rotation of the rollers (23). If the rollers (23) are very close, it may be preferable to put the nozzles (45) above the plane passing through the axes of the rollers (23) to spray a larger surface (61). On the , the nozzle (451) is placed below the plane of the axes of rotation of the rollers 23 and produces a cooling jet (461). On the , the nozzle (452) is placed above the plane of the axes of rotation of the rollers (23) and produces a cooling jet (462), the protective part (47) which should preferably be installed in this situation, does not is not shown. The jet (462) therefore sprays a larger surface of the blank (11) not shown than the jet (461).

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 this device (38) are given with the , there or the . A device (38) can be installed above the area opposite the rolling mill (54) and/or above the area next to the rolling mill (53). Preferably, said device (38) is an air blower which pushes the cooling fluid towards one of the edges (111) of the blank (11) and preferably gives the cooling fluid sufficient speed so that it does not run off. not on vocals (1111). The device (38) makes it possible to prevent the runoff of cooling fluid over the entire upper face of the blank (11). This contributes to guaranteeing controlled cooling in order to have good repeatability and good reproducibility of the heterogeneity of the temperature of the blank (11). Preventing the cooling fluid from streaming over the edge (1111) contributes to the thermal control of the edges of the blank (11), and in particular makes it possible to prevent the edges from being too cooled, which limits the appearance of creeks in the banks (111). When the upper cooling device is close to the cylinder (21), the device (38) for discharging the cooling fluid is advantageously supplemented or replaced by the cylinder (21) which acts as a dam blocking the runoff of the cooling fluid. . This makes it possible in particular to reduce the energy consumption of the device (38). A non-limiting example of the configuration in which the device (38) for evacuating the cooling fluid near the cylinder (21) is replaced by the cylinder (21) is illustrated by the .

In one embodiment, the conical jets of the upper cooling device (36) have a cone angle α of at most 20°, preferably substantially 15° or less and the cones of said conical jets have a substantially vertical axis. This configuration makes it possible to limit the runoff of the cooling fluid onto the blank (11). Preferably, the cooling system having at least one such conical jet is framed by a device for discharging the cooling fluid (38) as illustrated without limitation by the . The cone angle α is illustrated by the , the cone angle α is the angle of the cone of the coolant jet produced by the nozzles.

In another embodiment, the conical jets of the upper cooler (36) are angled from the vertical. The angle of inclination β is illustrated by the , this is the angle made by the axis of the nozzles with the straight line V perpendicular to the upper face of the blank (11). Preferably, the difference β-α/2 is greater than -20°, preferably substantially greater than -15°, more preferably positive or zero. Preferably, if the difference β - α/2 is negative, a cooling fluid evacuation device (38) is preferably installed to prevent runoff on the surface of the blank (11). If the cooling fluid jets of the upper cooling device (36) are close to the work cylinder (21), the axis of the cooling fluid jets (36) are advantageously oriented to bring the sprayed surfaces (51) closer to the work cylinder (21) to take advantage of the barrier effect of the cylinder (21). This configuration also makes it possible to increase the sprayed surfaces (51) to increase the cooling capacity of the cooling system. If the jets of cooling fluid are far from the working cylinder, it is advantageous to group the ramps of the upper cooling device (30) two by two and to orient the axes of the jets of cooling fluid (36) so as to bringing their respective sprayed surfaces (51) closer together. This configuration is advantageous because it causes the cooling fluid to concentrate in at least a part of the overlapping zone of the jets (36) and thus to reject the cooling fluid on the edges with enough velocity so as not to run off on the edges (1111) of the blank (11), which makes it possible not to cool the edges (111) of the blank (11) too much.

There is a non-limiting example of the previous embodiments. The nozzles close to the working cylinder (351) have their axis oriented towards the working cylinder (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°.

There is another non-limiting example of the previous embodiments. The nozzles near the working cylinder (351) are all inclined to bring the sprayed surfaces (51) closer to the working cylinder and the difference β – α/2 of the conical jets is positive or zero to avoid runoff of the cooling fluid on the blank (11).

There is another non-limiting example of the previous embodiments with conical vertical cooling jets (36) whose cone angle α is less than 20°.

There is another non-limiting example of the previous embodiments. The booms (303) and (304) are paired, the nozzles (353) and (354) are oriented so that the sprayed surfaces (513) and (514), illustrated by the , getting closer. The differences β – α/2 are positive or zero.

Preferably, for each cooling system, the upper sprayed convex envelope (52) faces each other with a tolerance of two, preferably once, the dimension of the diameter of the upper working cylinder (21) of the sprayed convex envelope bottom (62), preferably said convex envelopes (52, 62) are substantially opposite each other. The determination of the convex hulls is carried out by separating the different cooling systems. There illustrates a non-limiting example where there is a second cooling system. In this case, the convex hulls of each system are analyzed separately because one system cools before passing between cylinders (21) and (22) and the other after passing between cylinders (21) and (22). There shows an example with 3 cooling systems, two on either side of the reversible hot rolling mill and a third which is further away and which is used, in the case of this non-limiting example, for rapid cooling before joining a second hot rolling mill with its rolls (25) and (26). This arrangement is advantageous because it contributes to the thermal homogeneity of the blank (11). Placing said upper and lower convex envelopes (52, 62) of each cooling system facing each other is particularly advantageous because this allows uniform cooling in the thickness of the blank (11), which contributes to controlling the flatness of the blank (11), which is an important characteristic for blanks which are flat products.

Preferably, the set of nozzles (35) and (46) are capable of providing a surface flow per face of the blank (11) of cooling fluid of 1500 l/min/m² maximum, preferably of 600 to 1200 l/ min/m². This fluid can be propelled by a propellant gas. The cooling fluid can be water, deionized water, a liquefied or non-liquefied gas, preferably water emulsion, preferably deionized, and oil and rolling additives, which is used for lubrication cylinders (21) and (22) with the blank (11). Preferably, the deionized water has a resistivity greater than 105 kΩcm.

In one embodiment, the nozzles of the upper cooling device (35) are movable and maintained at a constant distance from the upper surface of the blank (11), preferably by being attached to the mechanism which holds the cylinder (21). This makes it possible to ensure better repeatability of the cooling of the blank (11). In another embodiment, the nozzles (35) are not movable. In this less expensive non-mobile embodiment, it is necessary to control the nozzles (35) which water the banks (111) or near the banks (111) accordingly, for example in the case where the nozzles (35) produce conical jets (36). Indeed, in the case of conical jets (36) projected by fixed nozzles (35), the distribution of cooling fluid on the edges (111) widens as the thickness of the blank decreases. during successive passes of the reversible hot rolling pattern. THE and 11b are non-limiting examples of this situation. The blank (11) is shown at the start of hot rolling with the and at the end of hot rolling with the each time with the same number of upper nozzles (35) which produce jets of cooling fluid (36). Due to the conical shape of the jets (36) and the reduction in the thickness of the blank (11), the edges (111) are not sprayed at the start of rolling illustrated in 11a whereas they are partially at the end of rolling illustrated in 11b.

In a preferred embodiment, illustrated by non-limiting example in , the nozzles (351) in the vicinity near the upper working cylinder (21) produce jets of cooling fluid (36) all of whose displacement components are projected onto the direction S of displacement of the blank (11), are oriented towards the work rolls (21) and (22) of the rolling mill. Preferably, the cooling fluid jets (36) of the upper cooling device are conical and the difference β-α/2 is positive or zero. In a more preferred embodiment as illustrated by , there is only one upper ramp (30) and two lower ramps (40).

In a preferred embodiment illustrated by the non-limiting example of the , the upper sprayed convex envelope (52) and the lower sprayed convex envelope (62), not represented on the , are close to the rolls of the rolling mill; preferably the maximum distance D55 and D65 to the cylinders (21) and (22) of the sprayed convex envelopes (52) and (62) are less than 3 times the largest of the diameters of the working cylinders (21) and (22) and / or the lengths D56 and D66 of said convex envelopes (52, 62) are less than two diameters, preferably a diameter of the largest of the working rolls (21) or (22). This embodiment is advantageous because it makes it possible to cool the blank (11) as soon as it leaves the grip of the cylinders (21) and (22) and to prevent the blank from moving too far from the cylinders before go back the other way for the next hot rolling pass. This is particularly advantageous as it improves the productivity of the hot rolling mill. Indeed the speed of reversible hot rolling mills is often limited to avoid overheating which results in burns, cracks, crocodiling or even ruptures of the blank (11).

In a preferred embodiment illustrated by a non-limiting example of the , there is a second cooling system on the other side of said hot reversible rolling mill, the second cooling system preferably being symmetrical to the first with respect to a plane passing through the axes of the work rolls (21) and (22 ). This arrangement is advantageous because it makes it possible to cool the blank (11) until it enters the grip of the reversible rolling mill and as soon as it leaves the grip of the reversible rolling mill on each rolling pass and in an identical manner.

In another preferred embodiment illustrated by a non-limiting example in FIGS. 4 and 13, the upper cooling device comprises at least one pair of ramps (303 and 304) of nozzles (353, 354), preferably 3 pairs of ramps ( 303 and 304), in each pair of ramps (303 and 304), the cooling fluid jets (363, 364) being oriented in opposition, the difference β – α/2 being positive or zero, preferably zero, α being l the angle of the cone of the jet of cooling fluid produced by the nozzles and β being the angle of inclination made by the axis of the nozzles (353, 354) with the straight line V perpendicular to the upper face of the blank (11 ), the sprayed surfaces (513, 514) of the blank (11) by the jets (363, 364) preferably overlapping by a factor between 1/3 and 2/3, preferably 1/2, and the device for lower cooling comprises at least one ramp (40) of nozzles (45), preferably 8 ramps (40), the fluid jets of which cooler (46) are conical and with an axis substantially normal to the blank (11). Preferably, the blank (11) is substantially horizontal. The angles are schematized in the general case on the with the nozzles (35), the ramps (30) and the jets of cooling fluids (36). There illustrates the sprayed surfaces (51). This configuration is advantageous because it causes the cooling fluid to concentrate in at least a part of the overlapping zone of the jets (36) and thus to reject the cooling fluid on the edges with enough velocity so as not to run off on the edges (1111) of the blank (11), which makes it possible not to cool the edges (111) of the blank (11) too much. This makes it possible to reduce the energy consumption of the devices (38) for discharging the cooling fluid, or even to be able to eliminate them.

In another preferred embodiment schematized without limitation in , the upper cooling device comprises at least one ramp (30), preferably 6 ramps (30), of nozzles (35) and the lower cooling device comprises at least one ramp (40), preferably 8 ramps (40), of nozzles (45), all of which produce conical jets of cooling fluid (36) and (46) whose axes are substantially perpendicular to the blank (11), and whose angle α of the cone of the jets (36) is less at 20°, preferably the angle α of the cone of the jets (36) is substantially 15°. This device has the advantage of being simpler to construct. The angle of the conical jets makes it possible to limit the horizontal component of the speed of the cooling fluid during its impact on the blank (11), and consequently to limit the spreading of the cooling fluid on the blank (11) to control cooling.

In another preferred embodiment illustrated without limitation by the and the the reversible hot rolling mill usable for the process according to the invention is part of a hot train in which the reversible hot rolling mill usable for the process according to the invention is preferably followed by a second hot rolling mill, shown schematically with its cylinders work (25) and (26), which can be a reversible rolling mill or a tandem rolling mill. In the embodiment illustrated by the , the cooling system of the reversible hot rolling mill usable for the process according to the invention is placed between the reversible hot rolling mill usable for the process according to the invention and the second hot rolling mill, preferably the distance between the cooling system and the second hot rolling mill being sufficient for the cooling system usable for the method according to the invention and the second hot rolling mill to operate independently. This arrangement is advantageous because it allows the cooling operation to be carried out in the production flow and without loss of capacity during the transfer of the blank from the first to the second reversible hot rolling mill. The distance between the cooling system and the second hot rolling mill is also important because, if it is sufficient in relation to the length of the blank, it allows for example to choose different speeds to pass through the cooling system and to pass through the second hot rolling mill. The length of the blank is evaluated by EP*LP/e, where EP is the thickness of the plate, LP the length of the plate and e the thickness of the blank between the two rolling mills. In the embodiment illustrated by the , there are three cooling systems for the reversible hot rolling mill that can be used for the process according to the invention, two systems positioned close to and on either side of the working rolls (21,22) and a system placed between the reversible hot rolling mill usable for the process of the invention and the second hot rolling mill, preferably the distance between the cooling system and the second hot rolling mill being sufficient for the cooling system usable for the process according to the invention and the second hot rolling mill operate independently.

An example of a hot rolling process for aluminum alloys includes the successive steps of

1. supply of an aluminum alloy rolling plate optionally plated at a hot rolling entry temperature,
2. performing a plurality of hot rolling and/or cooling passes with the reversible hot rolling mill usable for the invention, the cooling system being used at least once,
3. transfer of the blank (11) or the finished product in sheet or strip form to a hot rolling exit temperature for the continuation of the hot forming process.

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

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

The minimum length of the blank (11) can typically take the values of 2m, 3m, 4m, 5m. The maximum length of the blank (11) can typically take the values of 6m, 7m, 8m, 9m, 10m, 15m, 20m, 30m, 40m, 50m, 75m, 100m, 150m, 200m, 300m, 400m. Two constraints act to limit the maximum length of the blank (11). The first is the amount of metal in the rolling plate before the start of hot rolling. The order of magnitude of the maximum length will in this case be the length of the plate before the start of hot rolling 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 limitation of the length of the blank depends on the industrial installation in which the hot rolling mill is installed. For example, without limitation, if the industrial installation consists of a reversible hot rolling mill followed by a tandem hot rolling mill or a second reversible hot rolling mill, the maximum length is imposed by the distance between the reversible rolling mill usable for the method according to the invention and the tandem rolling mill or the second reversible hot rolling mill. This implies that all the configurations of lengths, thicknesses, before and after hot rolling listed above may not all be feasible depending on the industrial installation.

The plate is fed at a hot rolling inlet temperature. It may have been reheated and/or homogenized.

The reversible hot rolling mill usable for the process according to the invention carries out a plurality of hot rolling and/or cooling passes with the hot rolling mill. There can therefore be cooling passes without rolling, therefore without reducing the thickness of the blank. This feature is advantageous because it allows the cooling capacity of the cooling system to be increased if necessary. There may also be rolling passes without cooling, but the method according to the invention comprises at least one pass with cooling with the cooling system according to the invention. Since the plate is fed to the hot rolling inlet temperature, there is preferably no cooling before the first rolling pass. Operations such as end cutting, edging, cutting the blank into several smaller blanks, holding the blank, rotating the blank to change the orientation of hot rolling the blank (11) or the plate are usual operations during hot rolling. The examples of the steps mentioned are not limiting. The presence of said usual operations is not an interruption of hot rolling and does not limit the scope of the invention because they are part of the usual hot rolling operations.

The blank is then transferred to a hot rolling exit temperature of the reversible rolling mill that can be used for the process according to the invention. The hot rolling exit temperature is preferably at least 200°C, preferably at least 220°C, more preferably at least 240°C and more preferably at least 260°C. This hot rolling exit temperature is a compatible temperature for carrying out a second hot rolling. The blank (11) can be transferred to any usual stage on a hot mill: hot tandem rolling mill, second hot reversible rolling mill, hot coiling or hot cutting.

Preferably, the blank comprises an aluminum alloy of the AA6xxx, AA5xxx, AA7xxx, AA3xxx, AA2xxx series. Preferentially the draft includes an alloy chosen from AA3003, AA3004, AA3207, AA3104, AA4017, AA4025, AA5006, AA5052, AA5083, AA5086, AA5088, AA5154, AA5182, AA5251, AA538 , AA6016, AA6022, AA6056, AA6061, AA6111, AA6181, AA6216, AA6316, AA6451, AA6501, AA6502, AA6603, AA6605, AA6607, AA7072 AA7075, and an alloy of composition, in % by weight, preferably <0.5, Si<0.5, 0.3, Fe<0.7, preferably <0.3, Mn <1.9, preferably 1-1.5, Cu<1.5, preferably 0.5-1, preferably 0.5-0.8, Ti<0.15, preferably <0.1, Mg <0.5, preferably <0.3, preferably <0.05, remains aluminum and the inevitable impurities 0.05 maximum each and 0.15 in total. Optionally, the blank is plated on one or two sides, with one or more aluminum alloys from the AA1xxx, AA4xxx or AA7xxxx series, and preferably AA4004, AA4104, AA4045, AA4343, AA7072.

Preferably, the heterogeneity of the surface temperature of the blank (11) after its release from the grip of the rolling mill and the cooling device is less than 20°C and preferably less than 10°C. This characteristic, obtained thanks to the cooling system usable for the process according to the invention, is useful for improving the repeatability of the metallurgical properties of the products. The heterogeneity of the blank (11) is defined as the difference between the temperature of the hottest point of the blank (11) with the temperature of the coldest point of the blank (11) except on the edges ( 111) and/or except on the ends (112) and alternatively as the difference between the temperature of the hottest point of the blank (11) with the temperature of the coldest point of the blank (11).

With a hot rolling mill without the use of a cooling system that can be used for the method of the invention, the edges (111) are naturally colder than the rest of the blank (11) given the heat exchange surface. singing (1111). The lower temperature of the edges (111) is a cause of the cracks or cracks on the edges which reduce the useful width of the blank or which can cause it to break. The edges (111) of the blank (11) are therefore preferably less cooled than the rest of the blank by spraying the edges less than the rest of the blank (11). Preferably, the nozzles (35) and (45) whose jets (36) and (46) could spray the banks (111) are closed so as not to spray said banks (111). THE and 11b show a non-limiting example with a section along a plane perpendicular to the direction S passing through the upper (30) and lower (40) ramps. Certain upper (35) and lower (45) nozzles are closed so as not to spray the banks (111).

With a hot rolling mill without the use of a cooling system that can be used for the method of the invention, the ends (112) are naturally colder than the rest of the blank (11) given the heat exchange surface. extra at the ends. The lower temperature of the ends (112) is a cause of refusal of engagement of the blank during hot rolling. With a rolling mill that can be used for the process of the invention, the ends (112) are therefore preferably less cooled than the rest of the blank by spraying the ends (112) less than the rest of the blank (11). Preferably, the nozzles (35) and (45) whose jets (36) and (46) could spray the ends (112) are closed during the passage of these ends. This function is preferably achievable by the individual supply of each nozzle (35) and (45) by a quick-response valve (49) whose response time is advantageously less than 1 s, preferably less than 0.5s, and more preferably less than 0.2s. The fast response valves (49) are illustrated by the non-limiting example of Figures 5a and 5b.

The cooling fluid is preferably in calefaction on the blank. Calefaction is a thin layer of vapor that appears between a fluid on a surface whose temperature is high enough (Leidenfrost effect). This is advantageous because it ensures a homogeneous heat exchange compared to the situation where there are areas of the surface on which the fluid is not in calefaction.

Preferably, a thermal model calculates the sprinkling width and chooses the mode of cooling at the ends (112), preferably the thermal model presets the hydraulic system which supplies the booms (30) and (40), then at each pass the thermal model compares the desired temperature with the calculated or measured temperature of the blank (11), and the thermal model controls the valves (49) of the nozzles (35) and (45) according to the position of the blank (11), preferentially, the thermal model manages the upper (35) and lower (45) nozzles differently.

Preferably, the principle of the control of the cooling system is as schematized in . A thermal model coded on a computer or an automaton calculates the sprinkling width corresponding to the width of the blank. Preferably, the sprinkling width excludes the edges (111) to cool them as little as possible to reduce defects such as edge cracks. The thermal model chooses the end cooling mode (112). Preferably, the ends (112) are not sprinkled in order to cool them as little as possible in order to facilitate engagement in the hot rolling mill and reduce the phenomenon of crocodiling. Preferably, the model defines a pre-adjustment of the hydraulic system which supplies the ramps (30) and (40) so that the jets of cooling fluid (36) and (46) are established quickly as soon as the valves (49) open. . Then, on each pass, the thermal model compares the desired temperature with the calculated or measured temperature of the blank (11 The measured temperature can be obtained, for example, without limitation, by measuring the surface temperature by contactless infrared pyrometry or by a contact measurement on the surface of the blank ( 11 ). The calculated temperature can equally well relate to a surface temperature or an average temperature. The calculated temperature can be calculated with thermal simulation software, for example without limitation MSC Marc With the comparison between the desired temperature and the temperature of the blank (11), the thermal model controls the valves (49) of the nozzles (35) and (45) using the position and the dimensions of the blank ( 11).The position of the blank (11) can be calculated or measured.If there is no blank (11) between the upper and lower devices of the cooling system, the nozzles (35) and (45) are not powered for prevent, for example without limitation, that the jets (46) of the lower nozzles (45) spray the upper cylinder (21) or that the jets (36) of the upper nozzles (36) spray the lower cylinder (22) . The maximum heterogeneity of the surface temperature of the blank (11), preferably of the blank (11) except on the edges (111) and/or on the ends (112), after its release from the grip of the rolling mill and of the cooling device may be less than 20°C and preferably less than 10°C. Preferably, the thermal model manages the upper nozzles (35) and the lower nozzles (45) differently in order to avoid the formation of bridges or boats in the blank (11). Preferably, the absolute value of the temperature difference between the upper face and the lower face of the blank (11) is less than 10°C, more preferably 7°C, more preferably 5°C, more preferably 2°C. More preferably, the temperature of the upper face of the blank (11) is substantially equal to the temperature of the lower face of the blank (11).

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

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 coolant is in calefaction. The Leidenfrost temperature of the coolant sprayed on the blank depends on the nature of the coolant and its surface flow rate. The value of this temperature is typically and approximately around 300°C for the typical coolant, an emulsion of oil and rolling additives, which is lower than the usual hot rolling temperatures on a reversible rolling mill. The cooling system can cause a strong temperature heterogeneity between the surface and the core of the blank (11). By watering the blank (11) too long or too intensely, the surface temperature of the blank (11) is likely to be momentarily lower than the Leidenfrost temperature, which would significantly increase the risk of loss of thermal control in average value and in homogeneity of the blank (11) thus cooled. The thermal model therefore checks at each pass that the watering planned for the next pass does not risk generating a roughing temperature lower than the Leidenfrost temperature.

Preferably, the typical average cooling speed V of the average temperature of the blank (11) during the passage of the blank (11) between the upper (52) and lower (62) convex envelopes is of the order of V = C/e, where V is in °C/s, e is the thickness of the blank in mm, and C is a constant value which is between 400 and 1000, preferably between 600 and 900, more preferably between 700 and 800. The formula V=C/e is an approximation which requires in particular that the surface of the blank (11) remains above the Leidenfrost temperature. The decrease in the average temperature DT in degrees °C of the preform (11) after having passed through the upper (52) and lower (62) convex envelopes of the cooling system is typically of the order DT = C/e*d , d being the passage time of a point of the blank (11) between said convex envelopes, the speed of the blank (11) being constant. This formula is an approximation which requires in particular that the surface of the blank (11) remains above the Leidenfrost temperature. Preferably, the thickness range of the blank (11) for the application of said formulas has a minimum of 25mm, preferentially 50, preferentially 75mm, preferentially 100mm, preferentially 110mm and a maximum of 200mm, preferentially 175mm, preferentially 150mm, preferentially 140mm , preferably 130mm, preferably 125mm, preferably 120mm.

In a preferred embodiment, the hot rolling cycle time of a blank (11) in AA6xxx alloy, preferably in AA6016 alloy, is reduced by at least 30 seconds, preferably by at least 60 seconds, more preferably by at least 90 seconds with the method according to the invention, compared to rolling without the aid of said method. In a preferred embodiment, the hot rolling cycle time of a blank (11) made of the AA5182 alloy is preferentially reduced by at least 15 seconds to, preferentially by 20 s, more preferentially by 45 s compared to the rolling without the aid of said process. The cycle time is the duration between the start of the first pass and the end of the last hot rolling pass with the reversible hot rolling mill that can be used for the process of the invention.

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

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

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 plus or minus 10°C with respect to the temperature of the plate just before the start of hot rolling. Preferably, the temperature of the blank (11) remains substantially equal to the temperature of the plate before the start of hot rolling.

Detailed Description of Certain Embodiments

In a first embodiment illustrated by the , for each cooling system, the upper sprayed convex envelope (52) and the lower sprayed convex envelope (62) are close to the rolls of the rolling mill; preferentially the maximum distances D55 and D65 to the cylinders (21) and (22) of the sprayed convex envelopes (52) and (62) in the direction S are less than 3 times the largest of the diameters of the working cylinders (21) and ( 22) and/or the lengths D56 and D66 along the direction S of said convex envelopes (52, 62) are less than a diameter of the largest of the working rolls (21) or (22). Preferably, the convex envelopes (52, 62) are substantially opposite each other. This embodiment is advantageous because it makes it possible to cool the blank (11) as soon as it leaves the grip of the cylinders (21) and (22). This is particularly advantageous because the speed of reversible hot rolling mills is often limited to avoid overheating of the blank (11) which results in burns or even ruptures of the blank (11). This is particularly advantageous as it improves the productivity of the hot rolling mill. In fact, the speed of reversible hot rolling mills is often limited to avoid overheating which results in burns or even ruptures of the blank (11).

In this first embodiment, there is preferably a second cooling system on the other side of said reversible hot rolling mill whose is a non-limiting example. The second cooling system is preferably symmetrical to the first with respect to a plane passing through the axes of the work rolls (21) and (22). This arrangement is advantageous because it makes it possible to cool the blank (11) until it enters the grip and as soon as it leaves the grip of the reversible rolling mill on each rolling pass and in an identical manner.

This system is advantageous because it allows better control of the temperature of the blank during its reversible rolling and this at each pass, which is beneficial for the metallurgical quality of the product and for the productivity of said reversible rolling mill.

Other non-limiting examples of the first embodiment are given by the and the .

In the first preferred embodiment, the hot rolling cycle time of the blank (11) is preferentially reduced by at least 30 seconds for the AA6xxx alloys, preferentially for the AA6016 alloy, preferentially by 60s, more preferentially from 90s.

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

A second embodiment is a cooling system for rapidly cooling a blank (11) during hot rolling.

This embodiment is designed to spray each point of the blank (11) for 10s, preferably 8 seconds. Those skilled in the art will know how to adapt the characteristics below to their particular rolling mill and to the speed of the roughing (11).

In a preferred embodiment of the second preferred embodiment, illustrated without limitation by the , the upper cooling device comprises at least one pair of ramps (303 and 304) of nozzles (353, 354), preferably 3 pairs of ramps (303 and 304), in each pair of ramps (303 and 304), the jets of cooling fluid (363, 364) being oriented in opposition, the difference β - α/2 being positive or zero, preferably zero, the sprayed surfaces (513, 514) of the blank (11) by the jets (363, 364) preferably overlapping by a factor between 1/3 and 2/3, preferably 1/2, and the lower cooling device comprising at least 1 ramp (40) of nozzles (45), preferably 8 ramps (40), whose cooling fluid jets (46) are conical and have an axis substantially perpendicular to the blank (11). The angle β is the angle that the axis of the nozzles (353, 354) makes with the line V perpendicular to the upper face of the blank (11). The angle α is the angle of the cone of the jet of cooling fluid produced by said nozzles. These angles are schematized on the with the ramps (30), the nozzles (35) and the jets (36). This configuration is interesting because it causes the cooling fluid to concentrate in at least a part of the jet overlap zone (36) and thus to reject the cooling fluid on the edges with enough speed not to run off towards the edges. ends of the blank (11), thereby cooling the entire length of the blank uniformly. This system also makes it possible to reduce the energy consumption of the devices (38) for discharging the cooling fluid, or even to be able to eliminate them.

In another preferred embodiment of the second preferred embodiment, illustrated without limitation by the or the , the upper cooling device comprises at least 1 row (30) of nozzles (35), preferably 6 rows, and the lower cooling device comprises at least 1 row of nozzles (45), preferably 8 rows, all producing jets of cooling fluid (36) and (46) conical whose axes are substantially normal to the blank (11), and whose angle α of the cone of the jets (36) is less than 20°, preferably the angle of the cone jets (36) is substantially 15°. This device has the advantage of being simpler to construct. The angle α of the conical jets of less than 20°, preferably substantially 15°, makes it possible to limit the horizontal component of the speed of the cooling fluid during its impact on the blank (11), and consequently to limit runoff. cooling fluid on the blank (11) to control the cooling.

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

In another embodiment, it is possible to further cool the blank (11), for example by making two passes under the cooling system.

In another embodiment, it is possible to cool a thicker blank by 50° C. by reducing the speed of passage of the blank (11) or by increasing the length of the sprayed surfaces (51) and (61). By non-limiting example, a 140mm blank (11) can be cooled by 50°C in at least 15 seconds, preferably at least 10 seconds as shown in .

In another embodiment, the typical average cooling rate V of the average temperature of the blank (11) during the passage of the blank (11) between the upper (52) and lower (62) convex envelopes is the order of V= C/e, where V is in °C/s, e is the thickness of the blank in mm, and C is a constant value which is between 400 and 1000, preferably between 600 and 900, more preferably between 700 and 800. The formula V=C/e is an approximation which requires in particular that the surface of the blank (11) remains above the Leidenfrost temperature. The decrease in the average temperature DT in degrees °C of the preform (11) after having passed through the upper (52) and lower (62) convex envelopes of the cooling system is typically of the order DT = C/e*d , d being the passage time of a point of the blank (11) between said convex envelopes, the speed of the blank (11) being constant. This formula is an approximation which requires in particular that the surface of the blank (11) remains above the Leidenfrost temperature. Preferably, the thickness range of the blank (11) for the application of said formulas has a minimum of 25mm, preferentially 50, preferentially 75mm, preferentially 100mm, preferentially 110mm and a maximum of 200mm, preferentially 175mm, preferentially 150mm, preferentially 140mm , preferably 130mm, preferably 125mm, preferably 120mm.

The process for rolling an aluminum alloy of the AA6xxx series according to the invention comprises the steps:

1. casting of an alloy rolling plate of the AA6xxx series,
2. homogenization of the rolling plate, optionally followed by reheating,
3. first hot rolling to transform the rolling slab into a blank having a first output thickness from a first hot rolling start temperature,
4. cooling of the blank thus obtained with a typical average cooling rate from the average temperature of the blank of the order of V= C/e down to a 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 value which is between 400 and 1000, preferably between 600 and 900, more preferably between 700 and 800,
5. second hot rolling to transform the blank thus cooled into a strip with the final hot rolling thickness under deformation and temperature conditions such that the strip is recrystallized to at least 50%,
6. cold rolling the strip into a thin sheet.

The first hot rolling and the cooling are preferably carried out with a reversible hot rolling mill which can be used for the invention. During the cooling of step d, the cooling system is preferably used only once so as to preferentially reduce the average temperature with a typical average rate of cooling of the average temperature of the blank of at least 50° C. down to at an average temperature above 400°C. Preferably, the thickness range of the blank during this cooling has a minimum of 25mm, preferably 50, preferably 75mm, preferably 100mm, preferably 110mm and a maximum of 200mm, preferably 175mm, preferably 150mm, preferably 140mm, preferably 130mm, preferably 125mm, preferably 120mm.

In a preferred embodiment, during the cooling of step d, the cooling system is preferably used only once so as to reduce the average temperature of the blank by at least 50° C. to a higher average temperature at 400° C., in less than 10 seconds, preferably in less than 8 seconds for a blank (11) with a thickness of at most 114 mm.

The inventors have found, surprisingly, that this process makes it possible to improve productivity while retaining mechanical properties, surface quality and corrosion resistance at least equal to those obtained without the process according to the invention. These products can be particularly useful in the automotive industry, in particular for making exterior parts of the bodywork.

Among the AA6xxx series alloys, the preferred alloys are AA6005, AA6009, AA6013, AA6014, AA6016, AA6022, AA6056, AA6061, AA6111, AA6181, AA6216, AA6316, AA6451, AA6501, AA6502, AA6602, AA6602, AA6602, AA6602, AA6602, 7.

In one embodiment, the composition of the AA6xxx series alloy plate is an alloy comprising in % by weight: Si: 0.5 – 0.8; Mg: 0.3 – 0.8; Cu: maximum 0.3; Mn: maximum 0.3; Maximum Fe 0.5; Ti: maximum 0.15, aluminum remains and the inevitable impurities 0.05 maximum each and 0.15 their totality, and preferably Si: 0.6 – 0.75; Mg: 0.5 – 0.6; Cu: maximum 0.1; Min max 0.1; Fe 0.1 – 0.25; Ti: maximum 0.05, remains in aluminum and the inevitable impurities 0.05 maximum each and 0.15 in total.

In another embodiment the composition of the alloy plate of the AA6xxx series is an alloy comprising in % by weight: Si 0.7 – 1.3; Mg: 0.1 – 0.8; Cu: maximum 0.3; Mn: maximum 0.3; Maximum Fe 0.5; Ti: maximum 0.15, aluminum remains and the inevitable impurities 0.05 maximum each and 0.15 in total, and preferably Si: 0.8 – 1.1; Mg: 0.2 – 0.6; Cu: maximum 0.1; Min max 0.2; Fe 0.1 – 0.4; Ti: maximum 0.1, remains in aluminum and the inevitable impurities 0.05 maximum each and 0.15 in total.

After casting, the plate is preferably homogenized at a temperature between 500 and 570° C., and preferably between 540 and 560° C. typically for a period of at least 4 hours, and preferably for at least 8 hours. In a preferred embodiment, the maximum homogenization temperature is at most 555°C. Homogenization can be in one step or in several steps with increasing temperatures to reduce the risk of burning.

The plate is then rolled into a blank during a first hot rolling on a reversing rolling mill. The rolling start temperature of the first hot rolling is preferably above 470°C, more preferably above 490°C, and even more preferably above 500°C. Preferably, during this first hot rolling, the temperature is maintained above 450°C, preferably above 470°C and more preferably above 490°C. Preferably, the first outlet thickness is between 90mm and 140mm, preferably between 100 and 130mm, and more preferably between 110mm and 120mm.

This thickness of the blank is particularly interesting in factories whose hot rolling train consists of two successively reversible hot rolling mills and optionally a hot tandem rolling mill. Indeed, this blank thickness corresponds to the thickness of the blank during its transfer between the first reversible rolling mill and the second reversible rolling mill. Cooling can then be done without any loss of time.

The blank is then cooled at a cooling rate of at least 5°C/s from the average temperature of the blank to a second temperature at the start of the second hot rolling. Advantageously, the first hot rolling and the cooling are carried out with a reversible hot rolling mill that can be used for the process according to the invention, as illustrated in particular by FIGS. 12 to 15.

After cooling, the blank is rolled with a second hot rolling into a strip. The second hot rolling can be carried out successively on several hot rolling mills, for example a second reversible hot rolling mill followed by a tandem rolling mill or on the reversible hot rolling mill having been used for the first hot rolling followed by a tandem rolling mill. Preferably, the start temperature of the second hot rolling is between 380 and 450°C, more preferably between 400 and 440°C, and more preferably between 420 and 435°C. The strip is rolled to a final hot rolling thickness under conditions such that the strip after cooling is recrystallized to at least 50%, preferably at least 80%, and more preferably at least 90%, and particularly preferably at least 98%. A recrystallization of at least 50%, 80%, 90% and 98% respectively means that the recrystallization rate measured through the thickness and in at least 3 points of the width is respectively at least 50%, 80 %, 90% and 98%. Typically, recrystallization varies through thickness and can be complete at the surface and incomplete at mid-thickness. The preferred recrystallization rate depends on the strip alloy.

To obtain said recrystallization, it is advantageous for the outlet 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 reduction in thickness during the last pass of the second rolling is a parameter to ensure recrystallization. Said reduction of the last pass of the second hot rolling is at least 25%, preferentially at least 30%, preferentially 40%, and more preferentially at least 45%. The typical thickness of the strip obtained with the second hot rolling is between 4 and 10mm.

The strip is then cold rolled into a thin sheet. With the method of the invention, it is not necessary to carry out annealing and/or solution treatment between hot rolling and cold rolling or during cold rolling to obtain the mechanical properties, formability, surface condition or corrosion. Preferably, no annealing and/or solution treatment is carried out between hot rolling and cold rolling or during cold rolling. The thin sheet has a thickness typically between 0.5 and 2mm. In a preferred embodiment, the cold rolling reduction is between 70% and 80%. In another preferred embodiment, the reduction ratio between the strip and the thin sheet is at least 80% to obtain the most advantageous surface quality.

Preferably, after step f, an additional step can be performed

g: dissolution and quenching of the thin sheet thus obtained in a continuous heat treatment furnace.

Said continuous heat treatment furnace preferably operates in such a way that the holding time equivalent to 560°C, is less than 30 s, preferably less than 25 s and more preferably less than 20 s, the equivalent hold time being calculated using the equation

Q being an activation energy of 200 kJ/mol and R = 8.314 J/mol

Preferably, after the solution heat treatment and quenching, pre-tempering is optionally carried out, and the thin sheet matured at room temperature, so as to reach the T4 metallurgical state, is cut and shaped until obtain its final shape, is painted and hardened by baking

The thin sheet, after solution treatment in a continuous heat treatment furnace operating in such a way that the holding time equivalent to 560°C, , is less than 20 s, the equivalent hold time being calculated using the equation

Q being an activation energy of 200 kJ/mol and R = 8.314 J/mol,

reaches a tensile strength of at least 90% and preferably at least 95% of the maximum tensile strength obtained after solution treatment with a holding time equivalent to 560°C, , of 98s.

Thin sheet from cold rolling is particularly advantageous if only because it is easy to process by solution treatment. The conventional ranges aimed at obtaining a good surface condition, compatible with a quality for the exterior bodywork sheets, generally include an additional heat treatment during the transformation range with respect to the sheet obtained according to the invention. The presence of this additional heat treatment means that those skilled in the art need to use high temperatures and long equivalent holding times on solution treatment lines with continuous annealing in order to obtain sufficiently high mechanical strengths. in the metallurgical conditions as supplied and with after curing of the paints. On the contrary, the cold-rolled thin sheet of the invention can use a solution treatment in a continuous annealing line operating such that the equivalent holding time at 560°C, , is short, typically less than 25s, the equivalent hold time being calculated using the equation

Q being an activation energy of 200 kJ/mol and R = 8.314 J/mol.

Generally, the continuous annealing line operates in such a way that the heating rate of the thin sheet is greater than or equal to 10°C/s for a metal temperature lower than 400°C, the time spent at more than 530°C is between 15s and 90s, and the quenching rate is greater than or equal to 10°C/s, preferably greater than or equal to 15°C/s for a thickness of 0.9 to 1.1mm. Solution treatment causes the metal to reach a temperature below but close to the solidus temperature, typically above 530°C and below 570°C. The coiling temperature after the solution treatment is preferably between 50°C and 90°C, and preferably between 60°C and 80°C.

After the solution treatment and quenching, the thin sheet can be aged to reach the T4 metallurgical state, before being cut and shaped until obtaining its final geometry, painted and hardened by baking.

The method of the invention is particularly useful for the manufacture of thin sheets intended for the automobile industry which combine a high tensile elastic limit and a formability suitable for cold stamping operations, as well as excellent surface quality on the part and high corrosion resistance with high productivity.

In another preferred embodiment, the hot rolling mill combines the first preferred embodiment and the second embodiment.

A non-limiting example is given in . The hot rolling mill is surrounded by cooling systems which improve its productivity. A third cooling system enables rapid cooling during the transfer to the hot rolling suite. This embodiment makes it possible to combine the gain in productivity on the reversible hot rolling mill, the rapid cooling without impact on productivity during the transfer to the rest of the rolling, the whole making it possible to supply AA6xxx alloy sheets with good quality surface and improving the productivity of solution treatment and quenching lines.

Examples

Example 1:

A reversible hot rolling mill usable for the process according to the invention illustrated by the includes two cooling systems installed on either side of working rolls symmetrically. Each of these two cooling systems is composed of an upper cooling device and a lower cooling device. The upper cooling device comprises a ramp (30) of nozzles (35) directed towards the cylinder (21). Each upper nozzle ramp is protected by a protective piece (37). The lower cooling device comprises two ramps (40) of lower nozzles (45) installed below the plane of the axes of the rollers (23); a first ramp (40) between the first roll (23) from the cylinder (22) and the second roll (23), and the second ramp (40) of nozzles (45) between the second and the third roll (23) . The rollers (23) are close enough not to require the installation of a protective piece (47). Nozzles (35) and (45) produce full conical spray patterns. The nozzles (45) produce conical jets which are nearly tangent to the rollers (23). The nozzles (35) and (45) are fed by quick-response valves whose response time is 0.2s. The convex envelope of the upper sprayed surface is substantially opposite the convex envelope of the lower sprayed surface. Said convex envelopes are less than 3 diameters from the larger of the two working rolls of the hot reversible rolling mill. The average surface flow per surface is approximately 1200 l/min/m². The cooling fluid is the emulsion of the rolling mill which is used to lubricate the blank (11) during its hot rolling. The cooling fluid is in calefaction on the surface of the blank (11).

A 500 mm thick plate was hot rolled with cooling according to the invention at each hot rolling pass. There shows the thermal field on the upper surface of an AA6016 alloy blank measuring 2000 mm wide, 50 mm thick and 5000 mm long, just after the last reversible hot rolling pass. The heterogeneity of the surface temperature of the blank, including the edges and the ends, is 10°C both in length and in width.

An identical plate of the same alloy was also hot rolled but without the use of a cooling system usable for the method of the invention. There shows the thermal field on the upper surface of the blank obtained with the same dimensions as that presented in just at the exit of the last reversible hot rolling pass. The heterogeneity of the surface surface temperature of the blank is 25° C. both in the length and in the width in the absence of the use of the cooling system usable for the process of the invention.

In addition to the significant improvement in the thermal uniformity of the blank using the invention compared to practice without using the invention, the cooling of the blank during the rolling pattern makes it possible to reduce the reversible hot rolling cycle time of 90 seconds.

Two AA5182 alloy plates, 1480mm wide and 510mm thick were hot rolled with the invention, the first with the invention and the second without the invention. The hot rolling cycle time of the first plate was 64s shorter than the second.

Example 2:

A hot rolling mill usable for the method according to the invention comprising working rolls (21, 22) and a cooling system having six upper ramps (30) of nozzles (35) and eight lower ramps (40) of nozzles (45) is represented on the . It is part of a hot train comprising a second reversible rolling mill comprising working rolls (25,26). These two reversible hot rolling mills are part of a hot mill which additionally includes a hot tandem rolling mill. The nozzles of the upper ramps (35) are oriented perpendicular to the plane of the blank (11). The jets of the upper nozzles (36) are full conical, the cone angle of which is substantially 15°. The cooling fluid is the emulsion used to lubricate the work rolls during hot rolling. The nozzles (45) of the lower ramps (40) are oriented perpendicularly towards the lower face of the blank (11). The jets of the lower nozzles are full conical, the angle of the cone of which is substantially 90°. The sprayed surfaces (52) and (62) are substantially opposite each other.

The system is able to cool a sheet of 114mm thickness from a temperature of 470°C to an average temperature of 420°C in 8 seconds as shown in the graph of the obtained by numerical simulation. 20 seconds after the start of cooling, the heterogeneity in the thickness of the blank is around 9°C, and 30s after the start of cooling, the heterogeneity in the thickness of the blank is around 2 °C. In Table 1, Examples D and E, which are 114 and 109mm blanks in AA6xxx series alloy, were cooled with the system without any special tuning to have hotter edges or ends. The temperatures mentioned in Table 1 are measurements taken at the surface of the blanks. Given the transfer time greater than 30 s between the first reversible hot rolling mill and the cooling system and between the cooling system and the second reversible hot rolling mill, the surface temperatures of blanks D and E are representative of the average temperature of said blanks as well as core temperatures. Sheets D and E were therefore cooled by 57 and 75°C

AT B VS D E Reference Example A Reference Example B . Reference Example C Example D according to the invention- Example E according to the invention- Composition (% by weight) Whether 0.66 0.67 0.70 0.69 0.69 Fe 0.14 0.15 0.14 0.15 0.15 Cu 0.01 0.01 0.01 0.01 0.01 min 0.08 0.07 0.09 0.07 0.07 mg 0.64 0.64 0.52 0.54 0.56 CR 0.01 0.01 0.01 0.01 0.01 You 0.03 0.04 0.05 0.05 0.04 Plate heat treatment homogenization 6.5h 554°C 6.7h 554°C 30h 554°C 8 p.m. 554°C 4 p.m. 554°C cooling N / A N / A ambient temperature N / A N / A reheating N / A N / A at rolling temperature N / A N / A First hot rolling rolling start temperature (°C) 554 553 393 511 537 Final thickness(mm) 114 114 114 114 109 end of rolling temperature (°C) 524 523 360 481 507 cooling cooling rate N / A N / A N / A 5°C/s 5°C/s second hot rolling rolling start temperature (°C) 519 519 356 424 432 Final hot rolling thickness (mm) 3.05 3.05 6.35 5.08 5.08 reduction to the last hot pass 41% 39% 44% 47% 47% winding temperature (°C) 332 327 343 352 357 cold rolling cold reduction (%) 73.7 73.8 85.0 81.3 81.3 final thickness (mm) 0.8 0.8 0.95 0.95 0.95

Five plates whose compositions are given in Table 1 in% by weight were cast. Table 1 also details the transformation process. Columns A and B describe a plate and its stages of transformation into blank then strip then thin sheet to produce internal bodywork elements which have no requirement in terms of surface quality. Column C describes a plate and its typical transformation steps into a blank then into a strip then into a thin sheet to produce external bodywork elements which have high requirements in terms of surface quality. These are reference examples in which cooling is not carried out during hot rolling. Columns D and E are examples of the invention.

The 5 plates A, B C D and E were homogenized with the conditions of Table 1. The plates A, B, D and E were transferred to the first reversible hot rolling. Plate C was cooled to room temperature and then reheated to the start temperature of the first hot rolling and transferred to the first reversible hot rolling. The 5 plates were hot rolled by the first hot rolling mill into a blank of 114mm thickness except plate E which was rolled into a blank of 109mm thickness. The 5 blanks were then transferred to the second reversible hot rolling mill by passing through the cooling system of the first hot rolling mill. Blanks A, B and C passed through the cooling system without being sprayed, and underwent only natural air cooling during their transfer to the second reversible hot rolling mill. Blanks D and E passed through the cooling system in operation and were therefore cooled down to the surface temperature indicated in Table 1. The 5 blanks were then rolled with the second reversible hot rolling mill, then with a rolling mill hot tandem in one band. Coming out of the hot tandem rolling mill, the strips were coiled according to the characteristics in Table 1. After cooling, the coils were cold rolled into thin sheets.

..

Samples of bands C, D and E were taken after the last hot rolling pass and before coiling. These samples were cooled rapidly by immersing them in a tub of water at room temperature. Then recrystallization kinetics were carried out in the laboratory by heating each sample at different temperatures, then the samples are cooled in a manner similar to the cooling of a coil after hot rolling. Metallographies were then carried out ( ) and the recrystallization rate assessed (Table 2).

Heating temperature 310°C 321°C 332°C 343°C 355°C 365°C VS Ref example 0% 75% 98% 100% 100% 100% D invention 0% 15% 33% 44% 95% 100% E invention 0% 6% 43% 94% 99% 100%

The quality of the surface condition in lineage (roping) was characterized on thin sheets A, B, D and E. The lineage is measured as follows. A sample measuring approximately 270 mm (in the direction transverse to the direction of rolling) by 50 mm (in the direction of rolling) is cut from the thin sheet. A tensile pre-strain of 15%, perpendicular to the direction of rolling, i.e. in the direction of the length of the sample, is then applied. The sample is then subjected to the action of a type P800 abrasive paper in order to reveal the lineage

The thin sheets D and E, produced according to the invention, have a conforming surface quality for producing external bodywork elements as shown in the for the thin plate D and the for the thin plate E. This is not the case for the thin plates A and B as shown in the for the thin plate A and the for thin sheet B. The cooling system demonstrates its usefulness for obtaining the surface quality with a more economical process by eliminating reheating as for thin sheet C, not characterized specifically in terms of surface quality, which is used to produce elements of external bodywork.

To evaluate the solutionization kinetics of the 3 thin sheets C, D and E, the following characterizations were carried out. Samples were taken after cold rolling up to the final thickness on the 3 thin sheets C, D and E. Various solution treatment heat treatments were first carried out on the samples by varying the solution treatment times. samples in a fluidized bed oven at 570°C. A long immersion period of 90 s at 570°C was used to bring the samples completely into solution. The duration of 90s at 570°C is equivalent to a duration of 98s at 560°C using the formula

Q being an activation energy of 200 kJ/mol and R = 8.314 J/mol.

. Shorter solution times in the fluidized bed furnace at 570°C were used to achieve incomplete solution treatment of the alloys. These solution heat treatments were all followed by water quenching up to 80°C and a pre-tempering treatment for 8 hours at 80°C. After these various solution heat treatments, then quenching and then pre-tempering, the samples were tempered for 2 hours at 205°C in an oil bath in order to reach the T6 metallurgical state.

Tensile tests were then carried out. The elastic limit (Rp0.2) obtained after the final tempering treatment to the T6 metallurgical state is used as an indicator of the quality of the samples in solution. Indeed, depending on the state of precipitation existing in the thin sheets, the dissolution time at the solution temperature (here 570 °C) necessary to dissolve these precipitates varies. For reasons of productivity on the production machines performing the solution heat treatment, it is advantageous for the solution heat treatment time to be as short as possible.

The results of the tensile tests of the 3 thin sheets C, D and E are indicated in table 3 and on the . On this graph, each measured elastic limit (T6YS) is normalized with the elastic limit obtained for the same thin sheet after a solution time of 90 seconds in the fluidized bed at 570°C (T6YSmax).

There shows that the dissolution kinetics of the two thin sheets D and E according to the invention is much faster than that of comparative example C. Indeed, after immersion for 50 s in the fluidized bed at 570° C., the elastic limit in the T6 state of examples D and E according to the invention has reached more than 99% of its maximum elastic limit at the T6 condition, while comparative example C is just over 98% of its maximum yield strength in the T6 condition. Similarly, after 30s in solution in the fluidized bed at 570°C, the elastic limit in the T6 state of examples D and E according to the invention has reached more than 98% of its elastic limit. maximum in the T6 condition, whereas comparative example C is at 96% of its maximum elastic limit in the T6 condition. Therefore, the invention additionally makes it possible to accelerate the productivity of the solution treatment.

time of immersion in the fluidized bed (s) at 570°C Elastic limit (T6YS – MPa ) Limit elastic in the T6 state divided by the maximum elastic limit at state T6 (T6YS/T6YS max) D invention 1 10 143 0.52 D invention 1 20 264 0.96 D invention 1 30 271 0.98 D invention 1 50 275 1.00 D invention 1 90 276 1.00 E invention 2 10 134 0.49 E invention 2 20 262 0.96 E invention 2 30 271 0.99 E invention 2 50 274 1.00 E invention 2 90 274 1.00 VS ref example 3 30 264 0.96 VS ref example 3 50 271 0.98 VS ref example 3 90 275 1.00

Claims (8)

Method for rolling an aluminum alloy of the AA6xxx series comprising the steps:

1. casting of AA6xxx series alloy rolling plate,
2. homogenization of the rolling plate, optionally followed by reheating,
3. first hot rolling to transform the rolling slab into a blank having a first output thickness from a first hot rolling start temperature,
4. cooling of the blank thus obtained with an average cooling rate from the average temperature of the blank of V= C/e to a 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 value which is between 400 and 1000, preferably between 600 and 900, more preferably between 700 and 800,
5. second hot rolling to transform the blank thus cooled into a strip with the final hot rolling thickness under deformation and temperature conditions such that the strip is recrystallized to at least 50%,
6. cold rolling the strip into a thin sheet.

Process according to Claim 1, characterized in that during the cooling of step d, a cooling system is used only once so as to reduce the average temperature of the blank by at least 50°C down to an average temperature above 400°C. Process according to Claim 1 or 2, characterized in that the temperature during the first hot rolling is maintained above 450°C, preferably above 470°C and more preferably above 490°C and/or the first exit thickness is between 90mm and 140mm, preferably between 100 and 130mm, and more preferably between 110mm and 120mm and/or the exit temperature of the second hot rolling is at least 345°C, preferably at least 350°C and more preferably at least 355°C. Process according to at least one of Claims 1 to 3, characterized in that the reduction of the last pass of the second hot rolling is at least 25%, preferentially at least 30%, preferentially 40%, and more preferentially at least 45 %. Process according to at least one of Claims 1 to 4, characterized in that the reduction by cold rolling is between 70% and 80%, or greater than 80%. Process according to at least one of Claims 1 to 5, characterized in that after step f, an additional step is carried out
g solution treatment and quenching of the thin sheet thus obtained in a continuous heat treatment furnace, preferably the continuous heat treatment furnace operates in such a way that the holding time is equivalent to 560°C, is less than 30 s, preferably less than 25 s and more preferably less than 20 s, the equivalent hold time being calculated using the equation

Q being an activation energy of 200 kJ/mol and R = 8.314 J/mol Process according to Claim 6, characterized in that after the solution treatment and the quenching, a pre-tempering is optionally carried out, and the thin sheet matured at ambient temperature, so as to reach the metallurgical state T4, is cut and shaped until it reaches its final shape, is painted and hardened by baking. Thin sheet obtained according to the process of any one of claims 1 to 6, such that after solution treatment in a continuous heat treatment furnace operating in such a way that the holding time equivalent to 560°C, , is less than 20 s, the equivalent hold time being calculated using the equation

Q being an activation energy of 200 kJ/mol and R = 8.314 J/mol,
it reaches a tensile strength of at least 90% and preferably at least 95% of the maximum tensile strength obtained after solution treatment with a holding time equivalent to 560°C, , of 98s.