Patent Application
20230219125
The invention relates to the field of rolling flat aluminum alloy products. More specifically, the invention relates to a hot reversing mill equipped with a particularly rapid, homogeneous, and reproducible cooling system for flat aluminum alloy products.
The invention also relates to a process executed by said hot reversing mill equipped with a cooling system enabling a better thermal control of the flat aluminum alloy products during rolling. The invention also relates to a sheet, the process whereof uses a cooling during hot rolling, which can be obtained with the invention.
A hot line for rolling aluminum alloys always includes a reversing mill (i.e. two-way rolling) also known as a roughing mill or blooming train and, optionally, a multi-cage mill also known as tandem mill, at the output whereof the still hot metal is rolled up. The number of passes and the stepover (reduction in thickness per pass) are dependent on the hardness of the product (the flow stress thereof) and obviously, on the power of the mill, in terms of torque and load. Productivity requires taking the greatest possible reductions at each pass. However, one is then limited by the capacity of the mill in terms of rolling load and/or rolling torque, as described for example in the article “Mise en forme de l'aluminium—Laminage—Patrick Deneuville, © Techniques de l'Ingénieur—2010”. During hot aluminum fabrications such as hot rolling, the temperature of the metal is always at least typically 200° C.
Hot lines are moreover known wherein two reversing mills succeed each other followed by a tandem mill.
Hot reversing mills are frequently production bottlenecks in factories and in the light of the considerable investments that they represent, increasing the productivity thereof is a major challenge and obviously it has always been sought to increase the capacity of the mill in terms of mill load and/or torque.
In the prior art, it has frequently been envisaged to enhance the productivity of tandem mills rather than that of the reversing mill. The applications hereinafter particularly relate to cooling methods or processes installed on finish rolling hot tandem mills.
The patent application WO201558902 relates to a table for hot rolling aluminum strips and a process for hot rolling an aluminum strip.
The aim of this application is that of proposing, for a table for hot rolling aluminum strips comprising a tandem finish rolling table with several cages including at least one reel mounted downstream in the rolling direction and at least one associated cooling section, a solution which makes it possible to adjust in the best way the cooling curves and the temperature-time trajectories in the product to be rolled during hot rolling of aluminum strips. For this purpose, the cooling section(s) are arranged in the output zone of the table for hot rolling aluminum strips, and at least one trimming shears installed downstream in the rolling direction is associated with the tandem finish rolling table.
The patent EP2991783 relates to a process for manufacturing a metallic strip. This patent relates to a process for manufacturing a metallic strip whereby the strip is rolled in a mill with several cages, is output behind the last cage of the mill in the direction of transportation and cooled in a cooling device. To obtain a favorable granular 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 mill cage to an additional rapid cooling, the cooling of the strip or sheet still taking place at least in part in the span of the last mill cage in the direction of transportation, the rapid cooling taking place by applying a cooling fluid via the top and via the bottom on the strip or sheet, the volume flow of cooling fluid applied via the bottom on the strip or sheet amounting at least to 120% of the volume flow of cooling fluid applied via the top on the strip or sheet.
The patent application WO200889827 relates to a device for cooling a metallic strip. This application relates to a device for cooling a metallic strip between two mill cages, the strip being guided on a top guiding element of planar design. Below the top guiding element is disposed a prilling element which drives cooling fluid through at least one opening in the top guiding element towards the bottom side of the strip. In order to obtain an enhanced prilling design, according to this application, at least two openings juxtaposed in the transversal direction to the feed direction of the strip are produced in the top guiding element and have an elongated shape. The longitudinal axis of the opening is oriented along an angle with respect to the feed direction of the strip.
Processes and equipment also exist for cooling slabs before starting to supply the hot mill.
The patent application WO2016/012691 relates to a cooling process and equipment. This application relates to a process for cooling an aluminum alloy rolling slab, after the metallurgical homogenizing heat treatment of said slab and prior to the hot rolling thereof, characterized in that the cooling by a value of 30 to 150° C. is performed at a rate of 150 to 500° C./h, with a homogeneity of less than 40° C. on the entire treated part of the slab. This application also relates to the installation for executing said process as well as said execution.
The patent application WO 2018/011245 relates to a process for manufacturing a 6xxx series aluminum alloy sheet comprising the following steps: casting a 6xxx series aluminum alloy to form an ingot; homogenizing the ingot; cooling the homogenized ingot at a cooling rate of at least 150° C./h directly to the hot rolling starting temperature; hot rolling the ingot to a final thickness and coiling at the final thickness after hot rolling under conditions making it possible to obtain a recrystallization rate of at least 50%; cold rolling so as to obtain a cold-rolled sheet. The process according to the invention is particularly useful for manufacturing sheets intended for the automotive industry which combine a high tensile yield strength and a formability suitable for cold drawing operations, as well as an excellent surface quality and a high corrosion resistance with a high productivity.
For 6000 series alloys, further modifications are also envisaged to enhance the productivity and/or metallurgical properties.
The patent application EP1165851 relates to a process for converting an ingot of a 6000 series aluminum alloy into a self-annealing foil. This process consists of subjecting the ingot to a homogenizing heat treatment in two steps, firstly 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 between 450° C. and 480° C., then at an arrival temperature between 320° C. and 360° C. A hot-rolled foil comprising an exceptionally low Cube recrystallization component is thus obtained.
The patent application US2016/0201158 relates to novel processes for increasing the productivity on a continuous annealing and solution heat treatment line for aluminum sheet products for the automotive industry suitable for a heat treatment having high T4 and post-curing strength and reduced roping. By way of non-limiting example, the processes according to the invention can be used in the automotive industry. The alloys suitable for a heat treatment and the processes according to the invention can also be applied in the maritime, aerospace, and transportation industries.
The patent application EP1375691 relates to rolled foil made of type 6000 aluminum alloy containing Si and Mg as main constituents and having an excellent formability sufficient for enabling flat flap machining, an excellent dent resistance, and a good hardening ability during curing of a coating. The alloy foil has an anisotropy with a Lankford coefficient greater than 0.4 or a resistance coefficient for cubic texture 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., even bending when the resistance at the conventional flow threshold exceeds 140 MPa by ageing at ambient temperature. The invention also relates to a process for producing rolled aluminum alloy foil, which consists of subjecting an ingot to a homogenizing treatment, cooling same to a temperature less than 350° C. at a cooling rate of 100° C./hour or more, optionally to ambient temperature, heating same once again to a temperature from 300 to 500° C. and subjecting same to a hot rolling, performing a cold rolling of the hot-rolled product, and subjecting the cold-rolled foil to a solution treatment at a temperature greater than or equal to 400° C. before performing a quenching.
The application EP0786535 relates to the homogenizing, at a temperature not less 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 by way of remainder, then the product obtained is cooled from a temperature not less than 500° C. to a temperature located in the range between 350 and 450° C., and the starting point whereof enables a hot rolling. The hot rolling step being completed at a temperature situated in the range between 200 and 300° C., the product obtained is subjected to a cold rolling at a reduction ratio not less than 50%, immediately prior to the solution treatment thereof. The cold-rolled product is then subjected to a solution treatment wherein it is kept at a temperature found in the range located between 500 and 580° C., at a temperature rise rate of not less than 2° C./s for at most 10 minutes, then the product obtain is subjected to a hardening during which it is cooled to a temperature not greater than 100° C., at a cooling rate not less than 5° C./s. A process is thus obtained for producing an aluminum alloy rolling ingot intended for a molding, which has a high strength and moldability, as well as an excellent external appearance on the post-molding surface thereof, which is used appropriately as a material intended for transport equipment parts, such as external rolling ingots for automobiles.
The patent application JP2015067857 relates to the provision of an excellent Al-Mg-Si-based aluminum alloy foil for automobile panel in terms of drawability, suitable for bending capable of processing flat bending, a shape stability property, hardening of coating galling and corrosion resistance, and providing a manufacturing method for this purpose, where an Al-Mg-Si-based aluminum alloy foil for automobile panel containing 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 types of Mn: 0.30% or less, Cr: 0.20% or less, and Zr: 0.15% or less, and the remainder Al with unavoidable impurities. A distribution of the density of the direction of the cube to a part of the depth of ¼ of the thickness of the foil from a surface is within a range of 10 to 25, a mean of the value r (r=(r+r+r×2)/4) is 0.50 or furthermore, an absolute value of an anisotropy index in the place of the value r Δr (Δr=(r+rr×2)/2) is 0.30 or less and a mean crystal particle diameter is 50 μm or less.
For metallurgical or productivity reasons, it can be envisaged to quench the strip after hot rolling.
A reversing mill followed by a “tank” wherein the metal at the final thickness is immersed to be cooled is known (“Mise en forme de l'aluminium—Laminage—Patrick Deneuville, © Techniques de l'Ingénieur—2010”).
The patent application WO2019241514 relates to systems and processes for quenching a metallic strip after rolling. This application relates to systems and processes for quenching a metallic substrate, comprising the cooling of a top surface and a bottom surface of the metallic substrate until a strip temperature is cooled to an intermediate temperature. The cooling of the top surface of the metallic substrate is interrupted when the strip temperature reaches the intermediate temperature, and the cooling of the bottom surface of the metallic substrate continues until the metallic substrate reaches a target temperature, the target temperature being less than the intermediate temperature.
Patent application FR2378579 relates to a process for the rapid cooling of a continuous casting bar, rod or slab bar, resting on a track and sprayed with water. According to this application, this process is characterized in that said bar is moved by a to-and-fro movement during the entire cooling time, the travel of this movement being greater in the direction of extraction than in the opposite direction.
U.S. Pat. No. 6,309,482 relates to the in-line combination of a reversing mill (Steckel mill) and of the coil furnaces thereof with an accelerated cooling machine controlled immediately downstream therefrom and the associated process for sequentially rolling steel reversibly to obtain an overall reduction of at least around 3:1.
U.S. Pat. No. 9,643,224 relates to a device for cooling rolled products, preferably for cooling during cold rolling, comprising a nozzle for the application of a cooling agent on the rolled products, a cooling chamber in fluidic communication with the nozzle and extending substantially parallel with the plane of travel of the strip being provided for the application of the cooling agent on the rolled products.
Patent EP2979769 relates to a method and an installation for manufacturing a steel rolling ingot whereby a high-quality steel having less quality variation can be provided. It also relates to a process for manufacturing a steel sheet, comprising a step of hot rolling, a step of shape correction and a step of accelerated cooling in that order.
The problem addressed by the present invention is that of enhancing the productivity of reversing mills without degrading the metallurgical quality of the products obtained, or by enhancing the metallurgical quality and/or the productivity of the other fabrication steps. There is in particular a demand in the automotive industry for methods having a high productivity to provide superior-quality 6xxx alloy sheets, particularly in terms of mechanical strength, formability and assemblability, and surface appearance after painting.
The invention firstly relates to a hot reversing mill comprising two work rolls, a top work roll (21) and a bottom work roll (22), and at least one cooling system intended to cool a blank (11), said blank (11) moving on reels (23) and passing through the hot reversing mill between the two work rolls (21) and (22), said cooling system consisting of two cooling devices: a top cooling device of the blank (11) and a bottom cooling device of the blank (11) characterized in that:
The invention further relates to a process for hot rolling aluminum alloys comprising the successive steps of
The invention further relates to a process for hot rolling an AA6xxx series aluminum alloy comprising the successive steps of:
The invention further relates to a sheet obtained according to the process according to the invention, such that after solution heat treatment in a continuous heat treat furnace operating such that the equivalent hold time at 560° C., teq560°, 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/K,
it attains a tensile strength of at least 90% and preferably at least 95% of the maximum tensile strength obtained after solution heat treatment with an equivalent hold time at 560° C., teq560°, of 98 s.
All the aluminum alloys in question hereinafter are described, unless specified otherwise, according to the rules and descriptions defined by the “Aluminum Association” in the “Registration Record Series” published regularly thereby.
The tempers in question are described as per the European standard EN-515.
The tensile static mechanical characteristics are determined by means of a tensile test as per the standard NF EN ISO 6892-1.
Unless specified otherwise, the definitions of the standard EN 12258 apply.
Blank denotes herein an intermediate aluminum alloy product obtained by rolling a rolling ingot such as an ingot or a foundry slab, optionally scalped, optionally clad with one or more aluminum alloys, intended for manufacturing a finished product in the form of strip sheets or foils made of aluminum alloy, optionally clad with one or more aluminum alloys. A blank is therefore a rolled product, the thickness whereof is intermediate between the rolling ingot and the finished product.
Unless specified otherwise, the term “mill” refers herein to a “reversing mill”.
Unlike the prior art wherein either the productivity of reversing mills is increased by increasing the capacity of the mill in terms of rolling load and/or torque, or the productivity of the prior or subsequent steps are enhanced, the present inventors succeeded in enhancing the productivity of the reversing mills without using these solutions.
The present inventors particularly observed that given the hardness thereof, most aluminum alloys tend to overheat excessively at each stepover. It is then necessary to slow the mill by performing less substantial stepovers for example or by leaving a waiting time between each rolling pass.
According to the invention, it was observed that cooling the blank during the hot rolling step makes it possible to enhance the productivity of a hot mill or create more economical novel manufacturing processes by removing production steps, while retaining an identical or enhanced metallurgical quality of the products. Thus, cooling the blank during rolling on reversing mills can also surprisingly make it possible to give the finished rolled product additional physical properties, such as mechanical properties, surface condition or corrosion resistance.
The hot reversing mill according to the invention comprises two work rolls, a top work roll (21) and a bottom work roll (22), and at least one cooling system intended to cool a blank (11), said blank (11) moving on reels (23) and passing through the hot reversing mill between the two work rolls (21) and (22), said cooling system consisting of two cooling devices: a top cooling device of the blank (11) and a bottom cooling device of the blank (11). The numerous other parts and systems of the hot mill well-known to those skilled in the art, for example, non-restrictively, back up rolls, motors, columns, spindles, are not represented in the figures.
The top cooling device comprises at least one bar (30) of nozzles (35) disposed substantially parallel with the axis of the top work roll (21), the nozzles (35) spraying with jets of cooling fluid (36) the top face of the blank (11). The bottom cooling device comprises at least one bar (40) of nozzles (45) disposed between the reels (23) or between the bottom work roll (22) and the nearest reel (23), substantially parallel with the axis of the bottom work roll (22), the nozzles (45) spraying with jets of cooling fluid (46) the bottom face of the blank (11), the axis of the jets of cooling fluid (46) being oriented substantially perpendicularly to the bottom surface of the blank (11).
The ends (112) correspond to the part of the blank (11) which is engaged first or which is disengaged last from the roll bite of the rolls (21) and (22). The ends (112) are represented in
For each cooling system, a top (52) respectively bottom (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) upon the first impact thereof on the blank (11). An example of convex envelope (52, 62) of the sprayed surfaces (51, 61) is illustrated by
As illustrated by
As illustrated by
As illustrated by
As illustrated by
For each cooling system, the zone opposite the mill (54) and the zone next to the mill (53) are surfaces which are part of a half-plane which contains the top convex envelope (52) of the blank (11) considered as the simplified parallelepiped in
For each cooling system, as illustrated in
For each cooling system, the zone next to the mill (53) is delimited by the line C1 and by the line D1 which is parallel with the line C1 and at the minimum distance D57 plus the radius R1 of roll (21) of the line C1.
The direction S is that of the movement of the blank (11).
According to
According to
In the embodiment illustrated in a non-limiting manner by
The embodiments illustrated in a non-limiting manner for example by
Preferentially, the bottom nozzles (45) produce jets of cooling fluid (46) which do not reach either the reels (23) or the roll (22) directly in the presence of the blank (11) and which are preferentially almost tangent to the reels (23) and the distance D67 whereof is preferentially greater than a radius of the bottom roll (22), more preferentially than the diameter of the bottom roll (22) and/or the top nozzles (35) produce jets of cooling fluid (36) which do not reach the top work roll (21) directly, preferentially the distance D57 is greater than the radius of the top roll (21), more preferentially the distance D57 is greater than the diameter of the top roll (21). In an embodiment illustrated by
Nozzles (24) illustrated in
Preferably, the bottom nozzles (45) are below the plane passing through the axes of rotation of the reels (23) located in the vicinity of said nozzles (45) and/or the bottom nozzles (45) are protected by a component (47) having openings to allow the jets of cooling fluid (46) to pass and/or the top nozzles (35) are protected by a component (37) having openings to allow the jets of cooling fluid (36) to pass. Protecting the nozzles (35) and (45) is advantageous as hot rolling can cause an opening of the ends (112) of the blank (11) called “crocodiling” by those skilled in the art and which strikes the nozzles. The blanks (11) can also during the hot rolling form bridges or boats, i.e. the blank (11) instead of being substantially planar can curve in the longitudinal direction on coming out of the mill, the ends of the blank (11) pointing upward or downward. Protecting the nozzles (35) and (45) from the blanks (11) is therefore advantageous to prevent damage of said nozzles. A non-limiting example of the components (37) and (47) protecting the nozzles (35) and (45) is illustrated in
Preferentially, each nozzle (35) and (45) is supplied individually by a rapid response valve (49) the response time whereof is advantageously less than 1 s, preferentially less than 0.5 s, and more preferentially less than 0.2 s.
In an embodiment, the nozzles (35) and (45) are suitable for producing jets of cooling fluid (36) and (46) in a flat and/or conical and/or cylindrical shape. If the shape of the jets is cylindrical, the cross-section of the roll is preferentially circular. In an embodiment, the nozzles (35) and (45) are suitable for producing jets of cooling fluid (36) and (46) by prilling, preferentially the nozzles (35) and (45) are suitable for producing jets of cooling fluid (36) and (46) by prilling, in a solid cone shape, referred to as conical jets. Conical jets (46) and (36) are a better configuration than flat or cylindrical jets. Indeed, conical jets enable a better distribution of the cooling fluid on the blank (11). This thus enables a more homogeneous heat exchange and it is thus possible to obtain a blank (11) with for example temperature heterogeneity of less than 20° C., preferentially of less than 10° C.
Preferentially, 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 reels (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 reels (23). If the reels (23) are very close, it can be preferable to place the nozzles (45) above the plane passing through the axes of the reels (23) to spray a larger surface area (61). In
Preferentially, for each cooling system, at least one device (38) for discharging the cooling fluid from the top surface of the blank (11) is installed above the blank. Non-limiting examples of this device (38) are given with
In an embodiment, the conical jets of the top cooling device (36) have a cone angle α of at most 20°, preferentially 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). Preferentially, the cooling system having at least one such conical jet is framed by a device for discharging the cooling fluid (38) as illustrated in a non-limiting manner by
In a further embodiment, the conical jets of the top cooling device (36) are inclined with respect to the vertical. The angle of inclination β is illustrated by
Preferentially, for each cooling system, the top sprayed convex envelope (52) is facing with a tolerance of twice preferentially once the dimension of the diameter of the top work roll (21) of the bottom sprayed convex envelope (62), preferentially said convex envelopes (52, 62) are substantially facing. The determination of the convex envelopes is conducted by separating the different cooling systems according to the invention.
Preferentially, all of the nozzles (35) and (46) are suitable for supplying a surface flow per face of the blank (11) of cooling fluid of 1500 I/min/m2 maximum, preferentially of 600 to 1200 I/min/m2. This fluid can be propelled by a propellant gas. The cooling fluid can be water, deionized water, an optionally liquefied gas, preferentially the emulsion of water, preferentially deionized, and oil and rolling additives, used for lubrication of the rolls (21) and (22) with the blank (11). Preferentially, the deionized water has a resistivity greater than 105 kΩcm.
In an embodiment, the nozzles of the top cooling device (35) are movable and maintained at constant distance from the top surface of the blank (11), preferentially while being attached to the mechanism maintaining the roll (21). This makes it possible to ensure a better repeatability of the cooling of the blank (11). In a further embodiment, the nozzles (35) are not movable. In this less costly non-movable embodiment, it is necessary hence to pilot the nozzles (35) spraying the edges (111) or in the vicinity of the edges (111) for example in the case where the nozzles (35) produce conical jets (36). Indeed, in the case of the conical jets (36) sprayed by fixed nozzles (35), the distribution of cooling fluid onto the edges (111) widens as the thickness of the blank decreases during successive passes of the hot reversing rolling diagram.
In a preferred embodiment, illustrated by way of non-limiting example in
In a preferred embodiment illustrated by the non-limiting example in
In a preferred embodiment illustrated by a non-limiting example of
In a further preferred embodiment illustrated by a non-limiting example in
In a further preferred embodiment represented schematically in a non-limiting manner in
In a further embodiment illustrated in a non-limiting manner by
The invention also relates to a process for hot rolling aluminum alloys comprising the successive steps of
The minimum width of the blank (11) can typically take the values of 100 mm, 200 mm, 300 mm, 400 mm,500 mm, 700 mm, 800 mm, 900 mm, and 1000 mm. The maximum width of the blank (11) can typically take the values of 1500 mm, 2000 mm, 2500 mm, 3000 mm, 3500 mm, 4000 mm, 4500 mm, and 5000 mm.
The minimum thickness of the blank (11) can typically take the values of 5 mm, 6.35 mm, 10 mm, 12 mm, 12.7 mm, 15 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm 100 mm, 110 mm 120 mm, 130 mm, 150 mm, 200 mm, and 250 mm. The maximum width of the blank (11), which typically is similar to that of the cast ingot, can typically take the values of 300 mm, 350 mm, 400 mm, 450 mm, 500 mm, 550 mm, 600 mm, 650 mm, 700 mm, and 800 mm.
The minimum length of the blank (11) can typically take the values of 2 m, 3 m, 4 m, 5 m. The maximum length of the blank (11) can typically take the values of 6 m, 7 m, 8 m, 9 m 10 m, 15 m, 20 m, 30 m, 40 m, 50 m, 75 m, 100 m, 150 m, 200 m, 300 m, 400 m. Two constraints apply to limit the maximum length of the blank (11). The first is the quantity of metal of the rolling ingot before the start of hot rolling. The order of magnitude of the maximum length will be in this case the length of the ingot before the start of the hot rolling divided by the thickness of the blank at the end of the hot rolling multiplied by the thickness of the ingot before the start of the hot rolling. The second limitation of the length of the blank is dependent on the industrial installation wherein the hot mill is installed. By way of non-limiting example, if the industrial installation consists of a hot reversing mill followed by a hot mill in tandem or a second hot reversing mill, the maximum length is set by the distance between the reversing mill according to the invention and the tandem mill or the second hot reversing mill. This implies that all the configurations of lengths, thickness, before and after hot rolling listed above may not all be feasible according to the industrial installation.
The ingot is provided at a hot rolling input temperature. It may have been reheated and/or homogenized.
The hot reversing mill according to the invention carries out a plurality of hot rolling and/or cooling passes with the hot mill. There can therefore be cooling passes without rolling, therefore with no reduction of the thickness of the blank. This function is advantageous as it makes it possible to increase the cooling capacity of the cooling system if required. There can therefore be rolling passes without cooling, but the process according to the invention comprises at least one pass with a cooling with the cooling system according to the invention. The ingot being provided at the hot rolling input temperature, there is preferably no cooling before the first rolling pass. The operations such as cutting the ends, edge trimming, cutting the blank into several smaller blanks, placing the blank on standby, rotating the blank to change the orientation of the hot rolling of the blank (11) or the ingot are routine operations during hot rolling. The examples of the steps mentioned are not limiting. The presence of said routine operations is not an interruption of the hot rolling and does not limit the scope of the invention as they belong to routine hot rolling operations.
The blank is then transferred at a hot rolling output temperature of the reversing mill according to the invention. The hot rolling output temperature is preferably at least 200° C., preferably at least 220° C., preferably at least 240° C. and preferentially at least 260° C. This hot rolling output temperature is a compatible temperature for carrying out a second hot rolling. The blank (11) can be transferred to any routine step on a hot table: hot tandem mill, second hot reversing mill, hot coiling, or hot cutting to length.
Preferentially, the blank comprises an AA6xxx, AA5xxx, AA7xxx, AA3xxx, AA2xxx series aluminum alloy. Preferentially, the blank comprises an alloy chosen from AA3003, AA3004, AA3207, AA3104, AA4017, AA4025, AA5006, AA5052, AA5083, AA5086, AA5088, AA5154, AA5182, AA5251, AA5383, AA5754, AA5844, AA6005, AA6009, AA6013, AA6014, AA6016, AA6022, AA6056, AA6061, AA6111, AA6181, AA6216, AA6316, AA6451, AA6501, AA6502, AA6603, AA6605, AA6607, AA7072 AA7075, and an alloy of composition, as a % by weight, Si<0.5, preferably <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, the remainder aluminum and unavoidable impurities, 0.05 maximum each and 0.15 the total thereof. Optionally, the blank is clad on one or two faces, with one or more aluminum alloys of the AA1xxx, AA4xxx or AA7xxxx series, and preferentially AA4004, AA4104, AA4045, AA4343, AA7072.
Preferentially, the heterogeneity of the surface temperature of the blank (11) after the release thereof from the roll bite of the mill and the cooling device is less than 20° C. and preferentially less than 10° C. This feature, obtained thanks to the cooling system according to the invention, is useful for enhancing 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 mill which is not equipped with the invention, the edges (111) are naturally colder than the rest of the blank (11) given the heat exchange surface area of the edge (1111). The bottom temperature of the edges (111) is a cause of tears or cracks on the edges which reduce the useful width of the blank or which can cause the fracture thereof. The edges (111) of the blank (11) are therefore preferentially cooled less than the rest of the blank by spraying the edges less than the rest of the blank (11). Preferentially, the nozzles (35) and (45) wherein the jets (36) and (46) could spray the edges (111) are closed so as not to spray said edges (111).
With a hot mill which is not equipped with the invention, the ends (112) are naturally colder than the rest of the blank (11) given the additional heat exchange surface area at the ends. The bottom temperature of the ends (112) is a cause of refusal of engagement of the blank during hot rolling. With a roll which is equipped with the invention, the ends (112) are therefore preferentially cooled less than the rest of the blank by spraying the ends (112) less than the rest of the blank (11). Preferentially, the nozzles (35) and (45) wherein the jets (36) and (46) could spray the ends (112) are closed during the passage of these ends. This function is preferentially feasible by the individual supply of each nozzle (35) and (45) by a rapid response valve (49) the response time whereof is advantageously less than 1 s, preferentially less than 0.5 s, and more preferentially less than 0.2 s. The rapid response valves (49) are illustrated by the non-limiting example of
The cooling fluid is preferentially in calefaction on the blank. Calefaction is a thin layer of vapor that appears between a fluid on a surface the temperature whereof is sufficiently high (Leidenfrost effect). This is advantageous as this ensures a homogeneous heat exchange with respect to the scenario where there are zones of the surface whereon the fluid is not in calefaction.
Preferentially, a thermal model calculates the spraying width and selects the cooling mode at the ends (112), preferentially the thermal model presets the hydraulic system which supplies the bars (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 top (35) and bottom (45) nozzles differently.
Preferentially, the control principle of the cooling system is as represented schematically in
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 dependent on the products to be produced. Preferentially, the control of the cooling system is integrated in the control system of the hot reversing mill which controls the rolling parameters.
Preferentially, the thermal device does not cool the surface of the blank (11) below the Leidenfrost temperature of the cooling fluid. The Leidenfrost temperature is the temperature above which the cooling fluid is in calefaction. The Leidenfrost temperature of the cooling liquid prilled on the blank is dependent on the nature of the cooling liquid and the surface flow thereof. The value of this temperature is typically and approximately about 300° C. for the typical cooling fluid, an emulsion and oil and rolling additives, which is less than the usual hot rolling temperatures on a reversing mill. The cooling system can cause substantial temperature heterogeneity between the surface and the core of the blank (11). By spraying the blank (11) for too long or too intensely, the surface temperature of the blank (11) is liable to be momentarily less than the Leidenfrost temperature, which would increase the risk of loss of thermal control in terms of mean value and homogeneity of the blank (11) cooled. The thermal model therefore checks at each pass that the spraying envisaged at the next pass is not at a risk of generating a blank temperature less than the Leidenfrost temperature.
Preferentially, the typical mean cooling rate V of the mean temperature of the blank (11) during the passage of the blank (11) between the top (52) and bottom (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 equals between 400 and 1000° C./s*mm, preferentially between 600 and 900° C./s*mm, more preferentially between 700 and 800° C./s*mm. The formula V=C/e is an approximation which particularly requires that the surface of the blank (11) remain greater than the Leidenfrost temperature. The mean temperature decrease DT in degrees ° C. of the blank (11) after having traversed the top (52) and bottom (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 particularly requires that the surface of the blank (11) remain greater than the Leidenfrost temperature. Preferentially, the thickness range of the blank (11) for the application of said formulas has a minimum of 25 mm, preferentially 50, preferentially 75 mm, preferentially 100 mm, preferentially 110 mm and has a maximum of 200 mm, preferentially 175 mm, preferentially 150 mm, preferentially 140 mm, preferentially 130 mm, preferentially 125 mm, preferentially 120 mm.
In a preferred embodiment, the hot rolling cycle time of a blank (11) made of AA6xxx alloy, preferentially of AA6016 alloy, is reduced by at least 30 seconds, preferentially at least 60 seconds, more preferentially at least 90 seconds with the process according to the invention, with respect to rolling without the assistance of said process. In a preferred embodiment, the hot rolling cycle time of a blank (11) made of AA5182 alloy is preferentially reduced by at least 15 seconds, preferentially 20 s, more preferentially 45 s, with respect to rolling without the assistance of said process. The cycle time is the time between the start of the first pass and the end of the final hot rolling pass with the hot reversing mill according to the invention.
In a further preferred embodiment, the cooling system is used preferentially once so as to reduce the mean temperature of the blank by at least 50° C. to a mean temperature greater than 400° C., in less than 10 seconds preferentially in less than 8 seconds for a blank (11) of a thickness of at most 114 mm.
In an embodiment, the cooling system makes it possible to control the temperature of the blank (11) on a predefined thermal path during the hot rolling. The thermal path is the progression of the temperature of the blank (11) for the duration of the hot rolling. The thermal path is a metallurgical choice dependent on the alloy, the desired properties of the finished product, and the capacities of the hot 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 the hot rolling does not vary by plus or minus 10° C. with respect to the temperature of the ingot immediately prior to the start of hot rolling. Preferentially, the temperature of the blank (11) remains substantially equal to the temperature of the ingot before the start of hot rolling.
In a first embodiment illustrated by
In this first embodiment, there is preferentially a second cooling system on the other side of said hot reversing mill of which
This system is advantageous as it enables better control of the temperature of the blank during the reversing rolling thereof at each pass, which is beneficial for the metallurgical quality of the product and for the productivity of said reversing mill.
Further non-limiting examples of the first embodiment are given by
In the first preferred embodiment, the hot rolling cycle time of the blank (11) is preferentially reduced by at least 30 seconds for AA6xxx alloys, preferentially for AA6016 alloy, preferentially 60 s, more preferentially 90 s.
In the first preferred embodiment, the hot rolling cycle time of a blank (11) is preferentially reduced by at least 15 seconds for AA5182 alloy, preferentially 20 s, more preferentially 45 s.
A second embodiment is a cooling system suitable for rapidly cooling a blank (11) during a hot rolling.
This embodiment is designed to spray each point of the blank (11) for 10 s, preferentially 8 seconds. Those skilled in the art will be able to adapt the features hereinafter to their specific mill and to the speed of the blank (11).
In a preferred embodiment of the second preferred embodiment, illustrated in a non-limiting manner by
In a further preferred embodiment of the second preferred embodiment, illustrated in a non-limiting manner by
In the second preferred embodiment, the cooling system is used preferentially once so as to reduce the mean temperature of the blank (11) by at least 50° C. to a mean temperature greater than 400° C., in less than 10 seconds preferentially in less than 8 seconds for a blank (11) of a thickness of at most 114 mm as shown in
In a further embodiment, it is possible to cool the blank (11) more for example by carrying out two passages under the cooling system.
In a further embodiment, it is possible to cool a thicker blank by 50° C. by reducing the passage speed of the blank (11) or by increasing the length of the sprayed surfaces (51) and (61). By way of non-limiting example, a 140 mm blank (11) can be cooled by 50° C. in at least 15 seconds, preferentially at least 10 seconds as shown in
In a further embodiment, the typical mean cooling rate V of the mean temperature of the blank (11) during the passage of the blank (11) between the top (52) and bottom (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 equals between 400 and 1000, preferentially between 600 and 900, more preferentially between 700 and 800. The formula V=C/e is an approximation which particularly requires that the surface of the blank (11) remain greater than the Leidenfrost temperature. The mean temperature decrease DT in degrees ° C. of the blank (11) after having traversed the top (52) and bottom (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 particularly requires that the surface of the blank (11) remain greater than the Leidenfrost temperature. Preferentially, the thickness range of the blank (11) for the application of said formulas has a minimum of 25 mm, preferentially 50, preferentially 75 mm, preferentially 100 mm, preferentially 110 mm and has a maximum of 200 mm, preferentially 175 mm, preferentially 150 mm, preferentially 140 mm, preferentially 130 mm, preferentially 125 mm, preferentially 120 mm.
A third preferred embodiment is a process for hot rolling an AA6xxx series aluminum alloy comprising the steps of:
The first hot rolling and the cooling are performed preferably with a hot reversing mill according to the invention. During the cooling of step d, the cooling system is preferentially used once so as to reduce preferentially the mean temperature with a typical mean cooling rate of the mean temperature of the blank by at least 50° C. to a mean temperature greater than 400° C. Preferentially, the thickness range of the blank during this cooling has a minimum of 25 mm, preferentially 50, preferentially 75 mm, preferentially 100 mm, preferentially 110 mm and has a maximum of 200 mm, preferentially 175 mm, preferentially 150 mm, preferentially 140 mm, preferentially 130 mm, preferentially 125 mm, preferentially 120 mm.
In an embodiment of the third preferred embodiment, during the cooling of step d, the cooling system is used preferentially once so as to reduce the mean temperature of the blank by at least 50° C. to a mean temperature greater than 400° C., in less than 10 seconds preferentially in less than 8 seconds for a blank (11) of a thickness of at most 114 mm.
The inventors discovered surprisingly that this process makes it possible to enhance productivity while retaining mechanical, surface quality and corrosion resistance properties 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 producing external car body components.
In the third preferred embodiment, among the AA6xxx series alloys, the preferred alloys are AA6005, AA6009, AA6013, AA6014, AA6016, AA6022, AA6056, AA6061, AA6111, AA6181, AA6216, AA6316, AA6451, AA6501, AA6502, AA6603, AA6605, AA6607.
In an embodiment of the third preferred embodiment, the composition of the AA6xxx series alloy ingot is an alloy comprising as a % by weight: Si: 0.5-0.8; Mg: 0.3-0.8; Cu: maximum 0.3; Mn: maximum 0.3; Fe maximum 0.5; Ti: maximum 0.15, the remainder aluminum and unavoidable impurities 0.05 maximum each and 0.15 the total thereof, and preferably Si: 0.6-0.75; Mg: 0.5-0.6; Cu: maximum 0.1; Mn maximum 0.1; Fe 0.1-0.25; Ti: maximum 0.05, the remainder aluminum and unavoidable impurities 0.05 maximum each and 0.15 the total thereof.
In a further embodiment of the third preferred embodiment, the composition of the AA6xxx series alloy ingot is an alloy comprising as a % by weight: Si 0.7-1.3; Mg: 0.1-0.8; Cu: maximum 0.3; Mn: maximum 0.3; Fe maximum 0.5; Ti: maximum 0.15, the remainder aluminum and unavoidable impurities 0.05 maximum each and 0.15 the total thereof, and preferably Si: 0.8-1.1; Mg: 0.2-0.6; Cu: maximum 0.1; Mn maximum 0.2; Fe 0.1-0.4; Ti: maximum 0.1, the remainder aluminum and inevitable impurities 0.05 maximum each and 0.15 the total thereof.
After casting, the ingot is preferentially homogenized at a temperature between 500 and 570° C., and preferably between 540 and 560° C. typically for a time of at least 4 hours, and preferably for at least 8 hours. In a preferred embodiment, the maximum homogenizing temperature is at most 555° C. The homogenizing can be in one step or in several steps with increasing temperatures to reduce the risk of incipient melting.
In the third preferred embodiment, the ingot is then rolled into a blank during a first hot rolling on a reversing mill. The rolling starting temperature of the first hot rolling is preferentially greater than 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 output thickness is between 90 mm and 140 mm, preferentially between 100 and 130 mm, and more preferentially between 110 mm and 120 mm.
This blank thickness is particularly advantageous in factories wherein the hot rolling table consists successively of two hot reversing mills and optionally a hot tandem mill. Indeed, this blank thickness corresponds to the thickness of the blank during the transfer thereof between the first reversing mill and the second reversing mill. Cooling can then be carried out without losing any time.
The blank is then cooled according to a cooling rate of at least 5° C./s from the mean blank temperature to a second starting temperature of second hot rolling. Advantageously, the first hot rolling and the cooling are performed with a hot reversing mill according to the invention, as illustrated particularly by
After cooling, the blank is rolled with a second hot mill into a strip. The second hot rolling can be carried out successively on several hot mills, for example a second hot reversing mill followed by a tandem mill or on the hot reversing mill having been used for the first hot rolling followed by a tandem mill. Preferably, the starting 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 preferentially at least 98%. A recrystallization of at least respectively 50%, 80%, 90% and 98% 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, the recrystallization varies through the thickness and can be complete on the surface and incomplete at mid-thickness. The preferred recrystallization rate is dependent on the alloy of the strip.
To obtain said recrystallization, it is advantageous that the output temperature of the second hot rolling be at least 345° C., preferably at least 350° C. and more preferentially at least 355° C. The reduction in thickness during the final pass of the second rolling is a parameter to ensure recrystallization. Said reduction of the final 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 10 mm.
The strip is then cold rolled into a sheet. With the method according to the invention, it is not necessary to perform an annealing and/or a solution heat treatment between the hot rolling and the cold rolling or during cold rolling to obtain mechanical, formability, surface condition or corrosion properties. Preferably, an annealing and/or a solution heat treatment is not carried out between the hot rolling and the cold rolling or during cold rolling. The sheet has a thickness typically between 0.5 and 2 mm. In a preferred embodiment, the reduction by cold rolling is between 70% and 80%. In a further preferred embodiment, the reduction rate between the strip and the sheet is at least 80% to obtain the most advantageous surface quality.
Preferentially, after step f, an additional step can be carried out
Said continuous heat treat furnace operates preferentially such that the equivalent hold time at 560° C., teq560° 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/K
Preferentially, after the solution heat treatment and the quenching, a pre-ageing is optionally performed, and the sheet ages at ambient temperature, so as to attain the temper T4, is cut out and formed until the final shape thereof is obtained, is painted, and hardened by curing
The sheet, after solution heat treatment in a continuous heat treat furnace operating such that the equivalent hold time at 560° C., teq560°, 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/K,
attains a tensile strength of at least 90% and preferably at least 95% of the maximum tensile strength obtained after solution heat treatment with an equivalent hold time at 560° C., teq560°, of 98 s.
The sheet obtained from the cold rolling is particularly advantageous if only because it is easy to treat by solution heat treatment. Conventional procedures aimed at obtaining a satisfactory surface condition, compatible with a quality for external car body sheets, generally include an additional heat treatment during the fabrication procedure 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 substantial equivalent hold times on the solution heat treatment lines with continuous annealing in order to obtain sufficiently high mechanical strengths in the tempers as supplied and after curing the paints. On the contrary, the cold-rolled sheet according to the invention can use a solution heat treatment in a continuous annealing line operating such that the equivalent hold time at 560° C., teq560°, is short, typically less than 25 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/K.
Generally, the continuous annealing line operates such that the heating rate of the sheet is greater than or equal to 10° C./s for a metal temperature less than 400° C., the time spent at over 530° C. is between 15 s and 90 s, and the quench 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 1.1 mm. The solution heat treatment ensures that the metal reaches a temperature below but close to the solidus temperature, that is to say generally greater than 530° C. and less than 570° C. The coiling temperature after the solution heat treatment is preferably between 50° C. and 90° C., and preferably between 60° C. and 80° C.
After the solution heat treatment and the quenching, the sheet can age so as to attain the temper T4, before being cut out and formed until the final geometry thereof is obtained, painted, and hardened by curing.
The process according to the invention is particularly useful for manufacturing sheets intended for the automotive industry which combine a high tensile yield strength and a formability suitable for cold drawing operations, as well as an excellent component surface quality and a high corrosion resistance with a high productivity.
In a fourth preferred embodiment, the hot mill combines the first preferred embodiment and the second embodiment.
A non-limiting example is given in
A hot reversing mill according to the invention illustrated by
A 500 mm thick ingot was hot-rolled with a cooling according to the invention at each hot rolling pass.
An identical ingot of the same alloy was also hot-rolled but without the use of a cooling system according to the invention.
In addition to the noteworthy improvement of the thermal uniformity of the blank using the invention with respect to practice without using the invention, the cooling of the blank during the rolling procedure makes it possible to reduce the hot reversing rolling cycle time by 90 seconds.
Two ingots made of AA5182 alloy, 1480 mm wide and 510 mm 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 ingot was 64 s shorter compared to the second.
A hot mill according to the invention comprising work rolls (21, 22) and a cooling system having six top bars (30) of nozzles (35) and eight bottom bars (40) of nozzles (45) is represented in
The system is capable of cooling a 114 mm thick sheet from a temperature of 470° C. to a mean temperature of 420° C. in 8 seconds as shown on the graph in
Five ingots, the compositions whereof are given in table 1 as a % by weight, were cast. Table 1 also details the fabrication process. Columns A and B describe an ingot and the fabrication steps thereof into a blank then into a strip then into a sheet to produce internal car body elements which have no requirements in terms of surface quality. Column C describes an ingot and the typical fabrication steps thereof into a blank then into a strip then into a sheet to produce external car body elements which have substantial requirements in terms of surface quality. These are reference examples wherein cooling is not carried out during the hot rolling. Columns D and E are examples of the invention.
The 5 ingots A, B C D and E were homogenized with the conditions of table 1. Ingots A, B, D and E were transferred to the first hot reversing rolling. Ingot C was cooled to ambient temperature then reheated to the starting temperature of the first hot rolling and transferred to the first hot reversing rolling. The 5 ingots were hot-rolled by the first hot mill into a 114 mm thick blank except ingot E which was rolled into a 109 mm thick blank. The 5 blanks were then transferred to the second hot reversing mill through the cooling system of the first hot mill. Blanks A, B and C passed through the cooling system without being sprayed, and only underwent natural air cooling during the transfer thereof to the second hot reversing mill. Blanks D and E passed through the cooling system in operation and were therefore cooled to the surface temperature indicated in table 1. The 5 blanks were then rolled with the second hot reversing mill, then with a hot tandem mill into a strip. On leaving the hot tandem mill, the strips were coiled according to the characteristics in table 1. After cooling, the 5 coils were cold-rolled into sheets.
Samples from strips C, D and E were taken after the final hot rolling pass and before coiling. These samples were cooled quickly by immersing them in a water tank at ambient temperature. Then recrystallization kinetics were carried out in a laboratory by heating each sample to different temperatures, then the samples are cooled similarly to the cooling of a coil after hot rolling. Metallographs were then produced (
The roping surface condition quality was characterized on sheets A, B, D and E. The roping is measured as follows. A sample measuring about 270 mm (in the transversal direction to the rolling direction) by 50 mm (in the rolling direction) is cut out from the sheet. A tensile pre-deformation of 15%, perpendicular to the rolling direction, i.e. in the direction of the length of the sample, is then applied. The sample is then subjected to the action of a P800 type sandpaper in order to reveal the roping.
Sheets D and E, produced according to the invention, have a compliant surface quality for producing external car body elements as shown in
To evaluate the solution heat treatment kinetics of the 3 sheets C, D and E, the following characterizations were conducted. Samples were taken after cold rolling to the final thickness on the 3 sheets C, D and E. Various solution heat treatments were first performed on the samples by varying the solution heat treatment times of the samples in a fluidized bed furnace at 570° C. A long immersion period of 90 s at 570° C. was used for the complete solution heat treatment of the samples. The time of 90 s at 570° C. is equivalent to a time of 98 s at 560° C. using the formula
Q being an activation energy of 200 kJ/mol and R=8.314 J/mol/K.
Shorter solution heat treatment times in the fluidized bed furnace at 570° C. were used to obtain an incomplete solution heat treatment of the alloys. These solution heat treatments were all followed by a water quenching to 80° C. and a pre-ageing treatment of 8 hours at 80° C. After these different solution heat treatments, followed by quenching then pre-ageing, the samples were annealed for 2 hours at 205° C. in an oil bath in order to attain the temper T6.
Tensile tests were then performed. The yield strength (Rp0.2) obtained after the final annealing treatment in the temper T6 is used an indicator of the solution heat treatment quality of the samples. Indeed, according to the precipitation state existing in the sheets, the solution heat treatment time at the solution heat treatment temperature (herein 570° C.) required to dissolve these precipitates varies. For productivity reasons on the production machines carrying out the solution heat treatment, it is advantageous that the solution heat treatment time be as short as possible.
The results of the tensile tests of the 3 sheets C, D and E are indicated in table 3 and in
| Number | Date | Country | Kind |
|---|---|---|---|
| FR2007191 | Jul 2020 | FR | national |
| FR2012174 | Nov 2020 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2021/051002 | 6/2/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63034845 | Jun 2020 | US |
