Aluminum alloy precision plates

Abstract

The present invention relates to plates with a thickness of between 8 and 50 mm made of aluminum alloy having the following composition, in % by weight: Si: 0.7 - 1.3; Mg: 0.6 - 1.2; Mn: 0.65 - 1.0; Fe: 0.05 - 0.35; at least one element chosen from Cr: 0.1 - 0.3 and Zr: 0.06 - 0.15; Ti < 0.15; Cu < 0.4; Zn < 0.1; other elements < 0.05 each and < 0.15 in total, remainder aluminum and to the method for manufacturing same. The plates according to the invention are particularly useful as precision plates, notably for the production of machine elements, for example assembly or control tools. The plates according to the invention have an improved dimensional stability notably during machining steps, while having sufficient static mechanical properties, and an excellent anodizability.

Description

TECHNICAL FIELD

[0001] The invention relates to aluminum alloy sheets of the 6xxx series, in particular intended for use as precision plates. PREVIOUS ART

[0002] Excellent dimensional stability is very important for applications involving precision sheet metal, which typically has a thickness between 8 and 150 mm. This type of product is typically used for the production of machine elements, particularly as reference plates for assembly or inspection tools. For these applications, it is particularly important to minimize any deformation of the sheet metal during machining, thus avoiding additional pre-machining or final rework operations.

[0003] Patent application EP2263811 relates to rolled products having a machined surface having a flatness of 0.2 mm or less. According to one embodiment of this patent application, the alloy contains 0.3 to 1.5% by mass of Mg, 0.2 to 1.6% by mass of Si, and in addition one or more elements selected from the group consisting of 0.8% by mass or less of Fe, 1.0% by mass or less of Cu, 0.6% by mass or less of Mn, 0.5% by mass or less of Cr, 0.4% by mass or less of Zn, and 0.1% by mass or less of Ti, the remainder being Al and unavoidable impurities.

[0004] Patent application WO2014 / 060660 relates to a vacuum chamber element obtained by machining and surface treatment of a sheet of thickness at least equal to 10 mm made of aluminum alloy of composition, in % by weight, Si: 0.4 - 0.7; Mg: 0.4 - 0.7; Ti 0.01 - < 0.15, Fe < 0.25; Cu < 0.04; Mn < 0.4; Cr 0.01 - < 0.1; Zn < 0.04; other elements < 0.05 each and < 0.15 in total, remainder aluminum.

[0005] Patent application WO2018 / 162823 relates to a vacuum chamber element obtained by machining and surface treatment of a sheet of thickness at least equal to 10 mm made of aluminum alloy of composition, in % by weight, Si: 0.4 -0.7; Mg: 0.4 -1.0; the ratio in % by weight Mg / Si being less than 1.8; Ti: 0.01 -0.15, Fe 0.08 - 0.25; Cu < 0.35; Mn < 0.4; Cr: < 0.25; Zn < 0.04; other elements < 0.05 each and <0.15 in total, remainder aluminum, characterized in that the grain size of said sheet is such that the average linear interception length measured in the L / TC plane according to standard AS TM E112, is at least equal to 350 / µm between surface and 1 / 2 thickness.

[0006] Patent application US2010018617 discloses an aluminum alloy for anodic oxidation treatment which comprises as alloying elements 0.1 to 2.0% of Mg, 0.1 to 2.0% of Si and 0.1 to 2.0% of Mn, each content of Fe, Cr and Cu being limited to 0.03 mass.% or less, and in which the remainder is composed of Al and unavoidable impurities. This application teaches in particular a homogenization treatment at a temperature above 550 ° C and below or equal to 600 ° C.

[0007] Patent application CN108239712 relates to a 6082 aluminum alloy plate for aviation and a method for manufacturing the same. The chemical components of the 6082 aluminum alloy plate include, in weight percentage, 1.0% to 1.3% Si, 0.1% to 0.3% Fe, 0.05% to 0.10% Cu, 0.5% to 0.8% Mn, 0.6% to 0.9% Mg, 0.06% to 0.12% Zn, not more than 0.05% Cr, not more than 0.05% Ti and the balance Al and unavoidable elements.

[0008] Patent application CN108239713 relates to an aluminum alloy plate for an electronic product and a method for manufacturing the aluminum alloy plate. The chemical components of the aluminum alloy plate for the appearance of the electronic product include, in weight percentage, 0.3% to 0.4% of Si, not more than 0.10% of Fe, not more than 0.05% of Cu, not more than 0.05% of Mn, 0.45% to 0.55% of Mg, not more than 0.05% of Zn, not more than 0.05% of Cr, not more than 0.05% of Ti and the balance Al and unavoidable elements. 6XXX family alloys for forging are also known.

[0009] Patent application WO2017 / 207603 discloses a hot rolled semi-finished aluminum alloy forging blank of the 6xxx series having a thickness in the range of 2 mm to 30 mm, and having a composition comprising, by weight. %, Si 0.65-1.4%, Mg 0.60-0.95%, Mn 0.40-0.80%, Cu 0.04-0.28%, Fe up to 0.5%, Cr up to 0.18%, Zr up to 0.20%, Ti up to 0.15%, Zn up to 0.25%, impurities each <0.05%, total <0.2%, balance aluminum, and wherein it has a substantially non-recrystallized microstructure. The application also relates to a method for manufacturing such a forging material from hot-rolled aluminum alloy of the 6xxx series. The method for manufacturing the forging blank does not include detenting and dimensional stability during machining is not a criterion for this type of product intended to be highly hot-deformed by forging.

[0010] Patent application US2005 / 095167 discloses a component or semi-finished part made from a hot-formed aluminum alloy, typically by forging, of the following composition by weight. %: silicon 0.9-1.3, magnesium 0.7-1.2, manganese 0.5-1.0, copper less than 0.1, iron less than 0.5, chromium less than 0.25, titanium less than 0.1, zinc less than 0.2, zirconium and / or hafnium 0.05-0.2 and other unavoidable impurities, the total amount of chromium and manganese and zirconium and / or hafnium being at least 0.4 by weight, mixed aluminum / silicon crystals being present in addition to magnesium silicide precipitates. Again, the manufacturing process of the forged blank does not include detention and dimensional stability during machining is not a criterion for this type of product intended to be strongly deformed when hot by forging.

[0011] There is a need for improved 6XXX series aluminum alloy sheets, especially precision sheets, exhibiting improved dimensional stability especially during machining steps, while having sufficient static mechanical properties, and excellent anodizing suitability. STATEMENT OF THE INVENTION

[0012] The invention is defined in the appended claims.

[0013] A first object of the invention is a method for manufacturing an aluminum alloy sheet with a final thickness of between 8 and 50 mm in which a) a rolling plate is cast from an aluminium alloy of composition, in % by weight, Si: 0.7 - 1.3; Mg: 0.6 - 1.2; Mn: 0.65 - 1.0; Fe: 0.05 - 0.35; at least one element chosen from Cr: 0.1 - 0.3 and Zr: 0.06-0.15; Ti < 0.15; Cu < 0.4; Zn < 0.1; other elements < 0.05 each and < 0.15 in total, remainder aluminium., b) said rolling plate is homogenized, c) said rolling plate is rolled at a temperature of at least 340 °C to obtain a sheet with a thickness of at least 12 mm, d) optionally a heat treatment and / or cold rolling of the sheet thus obtained is carried out, e) a solution treatment of the optionally heat-treated and / or cold-rolled sheet is carried out and it is quenched, f) said sheet thus solution-treated and quenched is relieved by controlled traction with a permanent elongation of 1 to 5%, g) the sheet thus stretched is tempered, h) optionally said sheet thus tempered is machined to obtain a sheet with a final thickness of at least 8 mm.

[0014] A second subject of the invention is a sheet of thickness (claim 10) between 8 and 50 mm made of aluminum alloy of composition, in % by weight, Si: 0.7 - 1.3; Mg: 0.6 - 1.2; Mn: 0.65 - 1.0; Fe: 0.05 - 0.35; at least one element chosen from Cr: 0.1 - 0.3 and Zr: 0.06- 0.15; Ti < 0.15; Cu < 0.4; Zn < 0.1; other elements < 0.05 each and < 0.15 in total, remainder aluminum, capable of being obtained by the process according to the invention.

[0015] Another object of the invention is the use of a sheet according to the invention as a precision sheet, in particular for the production of machine elements, for example assembly or control tools. FIGURES

[0016] [ Fig. 1 ] There Figure 1 shows the grain structure in @L / TC section after hot rolling to 25 mm thickness of the product in alloy A ( Figure 1a ) and alloy product B ( Figure 1b ) [ Fig. 2 ] There Figure 2shows the Taylor factor in the longitudinal direction measured at 1 / 12 of the thickness and at ½ thickness for alloy A and B sheets with final thicknesses of 20 mm and 25 mm. Fig. 3 ] There Figure 3 show the steps performed for measuring the deflection deviations. Figure 3A : initial measurement of bar deflection; Figure 3B machining to remove ¼ of the thickness, Figure 3C second measure. DETAILED DESCRIPTION OF THE INVENTION

[0017] The designation of alloys is made in accordance with the regulations of The Aluminium Association (AA), known to those skilled in the art. The definitions of metallurgical conditions are given in the European standard EN 515. Unless otherwise stated, the definitions of the standard EN12258-1 apply.

[0018] Unless otherwise stated, the compositions are expressed in % by weight.

[0019] Unless otherwise stated, the static mechanical characteristics, in other words the breaking strength R m , the conventional yield strength at 0.2% elongation R p0.2 and the elongation at break A%, are determined by a tensile test according to standard ISO 6892-1, the sampling and direction of the test being defined by standard EN 485-1.

[0020] According to the invention, improved sheets of aluminum alloy of the 6XXX series, in particular precision sheets, having improved dimensional stability in particular during the machining steps, while having sufficient static mechanical properties, and excellent anodizing ability are obtained thanks to the selection of composition in % by weight, Si: 0.7 - 1.3; Mg: 0.6 - 1.2; Mn: 0.65 - 1.0; Fe: 0.05 - 0.35; at least one element chosen from Cr: 0.1 - 0.3 and Zr: 0.06- 0.15; Ti < 0.15; Cu < 0.4; Zn < 0.1; other elements < 0.05 each and < 0.15 in total, remainder aluminum and the method according to the invention.

[0021] The composition according to the invention makes it possible in particular to obtain low deformation during the machining of the products. Without being bound by a theory, the present inventors believe that the composition according to the invention makes it possible to obtain an essentially non-recrystallized structure throughout the thickness after hot rolling, which surprisingly makes it possible, after solution treatment and quenching, stress relief and tempering, to obtain a product having very low internal stresses and therefore deforming little during machining.

[0022] The present inventors have found in particular that compared to a standard composition of the AA6082 alloy, the presence of a high quantity of Mn and at least one element chosen from Cr and Zr makes it possible to improve the properties.

[0023] Thus, the Mn content is between 0.65 and 1.0% by weight. Preferably, the minimum Mn content is 0.70%, advantageously 0.75% and preferably 0.80% or even 0.85%. Preferably, the maximum Mn content is 0.95%. In one embodiment of the invention, the Mn content is between 0.8 and 1.0% by weight.

[0024] For similar reasons, the presence of at least one anti-recrystallizing element chosen from Cr: 0.1 - 0.3% and Zr: 0.06- 0.15% is necessary. Cr is the preferred anti-recrystallizing element within the scope of the invention. Preferably, the minimum Cr content is 0.12%, advantageously 0.15% and preferably 0.18%. Preferably, the maximum Cr content is 0.28%, advantageously 0.25% and preferably 0.23%. In one embodiment of the invention, the Cr content is between 0.15 and 0.25% by weight and the Zr content is less than 0.05% by weight. If Zr is added alone or in combination with Cr, the preferred content is 0.08 - 0.1.3%.

[0025] The addition of Fe is also necessary. Thus, the Fe content is between 0.05 and 0.35% by weight. Preferably, the minimum Fe content is 0.06%, advantageously 0.07% and preferably 0.08%. Preferably, the maximum Fe content is 0.30%, advantageously 0.25% and preferably 0.15%, which can contribute in particular to obtaining the advantageous essentially non-recrystallized grain structure after hot rolling. In one embodiment of the invention, the Fe content is between 0.08 and 0.15% by weight.

[0026] Mg and Si are added to achieve the desired mechanical characteristics through the formation of Mg 2 Si.

[0027] The Mg content is between 0.6 and 1.2% by weight. Preferably, the minimum Mg content is 0.61%, advantageously 0.62% and preferably 0.63%. Preferably, the maximum Mg content is 1.1%, advantageously 1.0% and preferably 0.9% or even 0.8%. In one embodiment of the invention, the Mg content is between 0.6 and 0.8% by weight.

[0028] The Si content is between 0.7 and 1.3% by weight. Preferably, the minimum Si content is 0.72%, advantageously 0.75% and preferably 0.80%. Preferably, the maximum Si content is 1.2%, advantageously 1.1% and preferably 1.0% or even 0.95%. In one embodiment of the invention, the Si content is between 0.8 and 1.0% by weight. Preferably, the Si content is greater than the Mg content and preferably Si / Mg is greater than 1.1 and even more preferably greater than 1.2 or even 1.3 so as to further reinforce the mechanical characteristics by the presence of silicon phases.

[0029] The Ti content is less than 0.15% by weight. It may be advantageous to add Ti, in particular for grain size control during casting. In one embodiment of the invention, the Ti content is between 0.01 and 0.05% by weight.

[0030] The Cu content is less than 0.4% by weight. In an embodiment of the invention aimed at obtaining higher mechanical characteristics, an addition of Cu is carried out and the content is between 0.1 and 0.3% by weight. However, in the preferred embodiment, Cu is not added and is present only as an unavoidable impurity, its content being less than 0.05% by weight and preferably less than 0.04% by weight, in particular so as not to impair the anodizing ability.

[0031] The Zn content is less than 0.1% by weight. In one embodiment of the invention, an addition of Zn is carried out and the content is between 0.05 and 0.1% by weight. However, in the preferred embodiment, Zn is not added and is present only as an unavoidable impurity, its content being less than 0.05% by weight.

[0032] Other elements may be present as unavoidable impurities with a content of less than 0.05% by weight each and less than 0.15% by weight in total, the remainder being aluminum.

[0033] The manufacturing method according to the invention comprises steps of casting, homogenization, hot rolling, optionally heat treatment and / or cold rolling, solution treatment, quenching, stress relief, tempering and optionally machining.

[0034] In a first step, a rolling plate made of an aluminum alloy of the composition according to the invention is cast, preferably by vertical semi-continuous casting with direct cooling. The plate thus obtained can be scalped, i.e. machined, before the subsequent steps. The rolling plate is then homogenized. Preferably, the homogenization temperature is less than 550 °C. In an advantageous embodiment of the invention, the homogenization temperature is between 515 °C and 545 °C. Hot rolling is then carried out to obtain a sheet with a thickness of at least 12 mm, either directly after homogenization or after cooling and reheating to a temperature of at least 340 °C, preferably at least 370 °C and preferably at least 380 °C. The hot rolling temperature is preferably maintained at at least 340°C, preferably at least 350°C and more preferably at least 360°C or even at least 370°C.The hot rolling temperature is preferably at most 450°C and preferably at most 420°C. The exit temperature of the hot rolling is preferably at most 410°C and preferably at most 400°C. When the hot rolling temperature is too high, the grain size becomes too large, which affects the dimensional stability during machining. Preferably, the maximum reduction rate of the passes during hot rolling is less than 50%, preferably less than 45% and preferably less than 40%, or even more preferably less than 35%.In one embodiment of the invention, the maximum reduction rate of the hot rolling passes depends on the exit thickness of the hot rolling and is less than one hundredth of 1.56 times the thickness - 5.9, for example, for an exit thickness of 25 mm, the reduction rate of each pass during hot rolling is preferably less than one hundredth of 1.56 times 25- 5.9, i.e. 33.1%. The combination of the composition, homogenization and hot rolling conditions makes it possible to obtain an essentially non-recrystallized structure throughout the thickness of the hot rolled product. By essentially non-recrystallized throughout the thickness, it is meant that the recrystallization rate, regardless of the position in the thickness, is less than 10% and preferably less than 5%.

[0035] A heat treatment, in particular to restore the hot-rolled sheet, can optionally be carried out afterwards, advantageously at a temperature between 300°C and 400°C. Cold rolling, typically of 10 to 50%, can optionally be carried out following the heat treatment or independently.

[0036] The hot-rolled and optionally heat-treated and / or cold-rolled sheet then undergoes solution treatment followed by quenching. Solution treatment is preferably carried out at a temperature between 510 °C and 570 °C. Quenching is typically carried out by immersion or spraying with cold water. The solution-treated and quenched sheet is then stress-relieved by controlled traction with a permanent elongation of 1 to 5%, preferably 1.5 to 3%. The stress-relieving step is essential to obtain low internal stresses and therefore low deformations during machining. Stress-relieving by controlled traction is limited to geometries of constant cross-section to ensure homogeneous plastic deformation and therefore does not apply to forged products with complex shapes.

[0037] Finally, tempering is carried out, typically at a temperature between 150°C and 210°C, to preferably obtain a T6, T651 or T7 state.

[0038] In one embodiment, said sheet thus returned is finally machined to obtain a sheet with a final thickness of at least 8 mm. Advantageously, at least 1 mm, preferably at least 1.5 mm or more preferably at least 2 mm per face is machined so as to obtain a precision sheet.

[0039] The sheets that can be obtained by the process according to the invention have particularly advantageous properties.

[0040] The mechanical properties of the sheets according to the invention are particularly advantageous. The sheets according to the invention have a yield strength R p0.2 (TL) of at least 240 MPa, preferably at least 250 MPa and preferably at least 260 MPa, and / or a breaking strength R m (TL) of at least 280 MPa, preferably at least 290 MPa and preferably at least 300 MPa and / or an elongation at break A% of at least 8%, preferably at least 10% and preferably at least 12%.

[0041] The sheets according to the invention have a low level of internal stresses. Thus the product of the maximum deflection deviation in the L and TL directions multiplied by the rolling exit thickness is less than 4 and preferably less than 3.The deflection deviations considered to obtain the value of the maximum deflection deviation are on the one hand the deflection deviation between the deflection measured for a bar of dimension 400 mm x 30 mm x rolling exit thickness and the deflection measured for this same bar after machining of ¼ of its thickness, and on the other hand the deflection deviation between the deflection measured for the previous bar, i.e. the bar after machining of ¼ of the thickness compared to the rolling exit thickness, and the deflection measured for this previous bar after additional machining of ¼ of its thickness, all deflection measurements being carried out with the bar placed on two supports 390 mm apart and the deflections being expressed in mm, all measurements being carried out before the optional final machining step and in both directions L and TL.

[0042] The texture of the products according to the invention is also advantageous. The crystallographic texture can be described by a 3-dimensional mathematical function. This function is known in the art as an Orientation Density Function (ODF). It is defined as the volume fraction of the material dV / V having an orientation g to within dg: dV / V dg = f g = f φ 1 Φ φ 2 where (ϕ1, Φ, ϕ2) are the Euler angles describing the orientation g.

[0043] The FDO of each sheet is measured by the spherical harmonics method from four pole figures measured by X-ray diffraction on a traditional texture goniometer. As part of the invention, the pole figure measurements were carried out on samples cut at mid-thickness of the sheets.

[0044] The information contained in the FDO has been simplified, as known to those skilled in the art, in order to describe the texture as a proportion of grains contained in a discretized Euler space.

[0045] The Taylor factor is a geometric factor that describes the propensity of a crystal to deform plastically by dislocation slip. It takes into account the crystal orientation as well as the state of deformation imposed on the material. This factor can be seen as a multiplicative factor of the elastic limit, a high value of the Taylor factor indicating a 'hard' grain requiring the activation of many slip systems, unlike a low value of the Taylor factor which will indicate a 'soft' grain, easy to deform. For a polycrystalline aggregate, it is possible to calculate an average Taylor factor, representative of the plastic behavior of all the grains. From the texture measurements, the Taylor factor for a given direction of stress was calculated according to the method described by Taylor (GI Taylor Plastic Strain in metals, J. Inst. Metals, 62, 307-324; 1938).

[0046] Many methods derived from Taylor's initial model exist for calculating the Taylor factor and can give significantly different Taylor factor values. To overcome these differences, inventors compared Taylor factor ratios rather than absolute values.

[0047] For the sheets according to the invention, the ratio between the Taylor factor in the longitudinal direction measured at 1 / 12th of the thickness and 1 / 2 of the thickness is between 0.90 and 1.10, preferably between 0.92 and 1.08 and more preferably between 0.95 and 1.05, the measurements being carried out before the optional final machining step.

[0048] According to the invention, sheets according to the invention are used as precision sheets, in particular for producing a reference sheet, a control tool or a template. Indeed, the sheets according to the invention have improved dimensional stability, in particular during the machining steps, while having sufficient static mechanical properties and excellent anodizing suitability. EXAMPLE

[0049] In this example, rolling plates were prepared from an alloy whose composition is given in Table 1. Alloy A is a reference alloy while alloys B and C are alloys according to the invention. [Table 1] Alloys Cr Fe Mg Mn If You Zn Cu A 0,06 0,25 0,67 0,60 0,94 0,02 0,02 0,02 B 0,21 0,11 0,65 0,93 0,96 0,02 0,01 0,01 C 0,20 0,10 0,67 0,87 0,92 0,02 0,00 0,00 Composition of alloys in percentage by weight

[0050] The plates were homogenized at 535 °C and hot rolled to a thickness of 20 to 35 mm depending on the case. The hot rolling inlet temperature was between 390 and 410 °C, the end of rolling temperature was maintained at a value of at least 340 °C. The highest reduction during a hot rolling pass, which corresponded to the last pass, is given in Table 2. The plates thus obtained were solution treated at 540 °C, quenched, detained by controlled tension and tempered to obtain a T651 temper. The tempering conditions were 8 hours at 165 °C. In the last step, a 5 mm machining (2.5 mm per face) was carried out so that the final thickness was 5 mm less than the end of rolling thickness.

[0051] The static mechanical characteristics in tension, in other words the breaking strength Rm, the conventional yield strength at 0.2% elongation Rp0.2, and the elongation at break A%, were determined by a tensile test according to standard NF EN ISO 6892-1 (2016) in the long transverse direction (TL), the sampling and the direction of the test being defined by standard EN 485 (2016). The sampling is carried out before the last machining step. The characterizations were carried out in the long transverse direction.

[0052] The results are given in Table 2 [Table 2] Alloys Highest reduction during a hot rolling pass Final thickness (mm) R p0.2 (TL) MPa R m (TL) MPa Ag% A% A Y61803 44% 20 281 326 11,3 15,3 B Y61781 41% 20 281 319 8,6 15,1 B Y61779 42% 25 285 323 8,3 14,2 B Y61783 38% 30 285 326 8,6 14,9 C Z65438 36% 25 276 310 8,1 14,1 C Z65439 36% 30 277 311 7,5 13,4 Static mechanical properties

[0053] Residual stresses were assessed on the sheet before machining by measuring the average deflection on bars machined in the L or TL direction at ¼ and ½ thickness.

[0054] Two full-thickness bars are taken, in the L and TL directions, by sawing before final machining of the sheet metal. The sampling dimensions are: for the bar L direction: 430mm (L direction) x 35mm (TL direction) x thickness for the bar TL direction: 4.50mm (TL direction) x 35mm (L direction) x thickness.

[0055] The bars are then machined to obtain a bar of length L = 400mm, width l = 30mm and thickness e (sheet thickness). The as-rolled L-TL faces are not machined so that the thickness of the machined bars remains the thickness of the sheet.

[0056] For deflection measurements, the bar is placed on two supports 390 mm apart (the supports are represented by triangles 1 on the Figure 3 -A ). A displacement sensor (represented by an arrow 2 2 Figure 3A ) is used to measure the deflection of the bar.

[0057] The steps are as follows: An initial measurement of bar deflection is taken (see Figure 3A ), which gives the referenced values Deflection L ini and Deflection TL ini expressed in mm. The bar is then machined to remove ¼ of its thickness (see diagram Figure 3 B) . A second measurement is taken (See Figure 3 C) which gives the referenced values Deflection L 1 / 4 and Deflection TL 1 / 4 expressed in mm. The bar is machined again to remove an additional 1 / 4 of its thickness. Only half of the initial thickness then remains. A third measurement is taken which gives the referenced values Deflection L 1 / 2 and Deflection TL 1 / 2 expressed in mm.

[0058] In each machining step, heating is limited to 10°C so as to avoid any influence of the machining conditions on the deflection measurements taken.

[0059] The deflection deviations between ¼ and initial and then between ½ and ¼ are reported in Table 3 below, for the L and TL directions. The maximum deflection deviation multiplied by the rolling exit thickness is also reported. [Table 3] Alloys Rolling mill output thickness Final thickness (mm) Arrow spacing (mm) Maximum deflection deviation * rolling thickness Arrow L 1 / 4-Arrow L ini Arrow L 1 / 2 - Arrow L 1 / 4 TL 1 / 4 Arrow - TL ini Arrow TL 1 / 2 Arrow - TL 1 / 4 Arrow A 25 20 0,205 0,177 0,127 0,038 5,13 B 25 20 0,115 0,043 0,08 0,009 2,88 B 30 25 0,057 0,004 0,025 0,041 1,71 B 35 30 0,002 0,058 0,036 0,067 2,35 C 30 25 0,012 0,021 0,022 0,064 1,92 C 25 30 0,024 0,0231 0,032 0,043 1,51 Deflections measured on machined bars

[0060] With the reference alloy, the product of the maximum deflection deviation in the L and TL directions multiplied by the rolling exit thickness is greater than 5.1; whereas with the alloy according to the invention this product is always less than 3.

[0061] The grain structure was characterized for some tests after hot rolling. The results are presented on the Figure 1 . There Figure 1a shows the grain structure after anodic oxidation of alloy A after hot rolling to a thickness of 25 mm. Figure 1bshows the grain structure after anodic oxidation of alloy B after hot rolling to a thickness of 25 mm. On the Figure 1 a , we observe near the surfaces a recrystallized zone while the Figure 1b , this area is not observed the granular structure is fibrous, i.e. not recrystallized, throughout the thickness of the hot rolled product.

[0062] The texture of the products was measured on 50x50 mm samples in the L / TL plane in order to obtain the Taylor factor in the longitudinal direction. The results are presented in Table 4. For the products according to the invention, the ratio between the Taylor factor at 1 / 12th of the thickness and at ½ thickness is significantly lower than for the reference product. [Table 4] Alloys Final thickness (mm) Taylor factor at position T / 12 Taylor factor at position T / 2 Taylor factor ratio T / 12 / T / 2 A Y61803 20 1,12 0,99 1,13 B Y61781 20 1,12 1,05 1,07 B Y61779 25 1,07 1,08 0,99 Measured Taylor factors

Claims

1. Method for manufacturing an aluminum alloy plate with a final thickness of between 8 and 50 mm, wherein a) a rolling ingot is cast from aluminum alloy with the composition, as % by weight, Si: 0.7 - 1.3; Mg: 0.6 - 1.2; Mn: 0.65 - 1.0; Fe: 0.05 - 0.35; at least one element selected from Cr: 0.1 - 0.3 and Zr: 0.06 - 0.15; Ti < 0.15; Cu < 0.4; Zn < 0.1; other elements < 0.05 each and < 0.15 in total, the remainder aluminum, b) said rolling ingot is homogenized, c) said rolling ingot is rolled at a temperature of at least 340°C to obtain a plate with a thickness of at least 12 mm, d) optionally heat treatment and / or cold rolling of the plate thus obtained is carried out, e) a solution heat treatment of the plate, optionally heat treated and / or cold rolled is carried out, and it is quenched, f) said plate thus solution heat treated and quenched is stress relieved by controlled stretching with a permanent elongation of 1 to 5%, g) aging of the plate thus stretched is carried out, h) optionally said plate thus aged is machined to obtain a plate with a final thickness of at least 8 mm.

2. Method according to claim 1, wherein the Mn content is between 0.8 and 1.0% by weight.

3. Method according to claim 1 or claim 2, wherein the Cr content is between 0.15 and 0.25% by weight and the Zr content is less than 0.05% by weight.

4. Method according to any one of claims 1 to 3, wherein the Fe content is between 0.08 and 0.15% by weight.

5. Method according to any one of claims 1 to 4, wherein the Cu content is less than 0.05% by weight and preferably less than 0.04% by weight.

6. Method according to any one of claims 1 to 5, wherein the homogenizing temperature is between 515°C and 545°C.

7. Method according to any one of claims 1 to 6, wherein the hot-rolling temperature is maintained at least 350°C and the maximum rolling mill draft of the passes during hot rolling is less than 50%.

8. Method according to any one of claims 1 to 7, wherein the hot-rolling temperature is no more than 450°C and preferably no more than 420°C.

9. Method according to any one of claims 1 to 8, wherein the exit temperature of the hot rolling is no more than 410°C and preferentially no more than 400°C.

10. Plate with a thickness of between 8 and 50 mm made from aluminum alloy with a composition, as % by weight, Si: 0.7 - 1.3; Mg: 0.6 - 1.2; Mn: 0.65 - 1.0; Fe: 0.05 - 0.35; at least one element selected from Cr: 0.1 - 0.3 and Zr: 0.06- 0.15; Ti < 0.15; Cu < 0.4; Zn < 0.1; other elements < 0.05 each and < 0.15 in total, the remainder aluminum, able to be obtained by the method according to any one of claims 1 to 9, having a yield strength Rp0.2(LT) of at least 240 MPa, preferably at least 250 MPa and preferably at least 260 MPa, and / or an ultimate tensile strength Rm(LT) of at least 280 MPa, preferentially at least 290 MPa and preferably at least 300 MPa, and / or an elongation at rupture A% of at least 8%, preferentially at least 10% and preferably at least 12%, and, such that the product of the maximum deflection difference in the directions L and LT multiplied by the rolling-exit thickness is less than 4 and preferably less than 3, the differences in deflections considered for obtaining the maximum value being firstly the difference in deflection between the deflection measured for a bar of dimensions 400 mm x 30 mm x rolling-exit thickness and the deflection measured for this same bar after machining of ¼ of its thickness, and secondly the difference in deflection between the deflection measured for the previous bar and the deflection measured for this previous bar after supplementary machining of ¼ of its thickness, all the deflection measurements being made with the bar placed on two supports 390 mm apart and the deflections being expressed in mm, all the measurements being made before the optional final machining step.

11. Plate according to claim 10, wherein the ratio between the Taylor factor in the longitudinal direction measured at 1 / 12th of the thickness and 1 / 2 of the thickness is between 0.90 and 1.10, preferably between 0.92 and 1.08 and preferably between 0.95 and 1.05, the measurements being made before the optional final machining step.

12. Use of a plate according to any one of claims 10 to 11 as a precision plate, in particular for producing elements of machines, for example assembly or inspection equipment.

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