Method for manufacturing a 7xxx aluminum alloy plate and 7xxx aluminum alloy plate

Abstract

The present invention relates to plates with a thickness comprised between 6 and 25 mm made of an aluminum alloy with a composition, in weight %, Zn: 4.5-7.0; Mg: 1.2-3.5; Cu: 1.0-3.0; at least one element selected from among Cr: 0.04-0.35, Zr: 0.04-0.15 and Mn 0.04-0.5; Ti<0.25; Fe<0.6; Si<0.5; other elements <0.05 each and <0.15 in total, the remainder being aluminum and a manufacturing method thereof. The plates according to the invention are particularly useful as precision plates, in particular to make machine bases, reference plates, transport tables, assembly jigs, robot arms. The plates according to the invention have an improved dimensional stability in particular during the machining steps, while having sufficient static mechanical properties, and a good anodization capability.

Description

TECHNICAL FIELD

[0001] The invention relates to plates made of an aluminum alloy of the 7xxx series, intended in particular to be used as a precision plate.PRIOR ART

[0002] An excellent dimensional stability is very important for applications involving precision plates, whose thickness is typically comprised between 6 and 150 mm. This product type is typically used for making machine elements, in particular as reference plates for assembly or control tooling. For these applications, it is particularly important to reduce as much as possible any deformation of the plate during machining thereof, which allows avoiding additional pre-machining or final finishing operations.

[0003] Precision plates made of a 6xxx alloy are known, in particular from the application WO2021 / 064320 which discloses plates with a thickness comprised between 8 and 50 mm lade of an aluminum allow with a composition, in 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 among 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 being aluminum. These precision plates are particularly useful as precision plates, in particular for making machine elements, for example assembly or control tooling.

[0004] Moreover, the precision plates ALPLAN©7075 are known which combine a good dimensional stability with a high mechanical strength as well as a good flatness and a low roughness of the surfaces (cf.

[0005] https: / / www.constellium.com / sites / default / files / tid_product_documents / alplan_7075.pdf).

[0006] There is a need for improved plates made of an aluminum alloy of the 7XXX series, in particular precision plates, having an improved dimensional stability in particular during the machining steps, while having sufficient static mechanical properties, and an excellent anodization capability.DISCLOSURE OF THE INVENTION

[0007] A first object of the invention is a method for manufacturing a plate made of an aluminum alloy with a final thickness comprised between 6 and 25 mm, wherein, successively,

[0008] a) casting a rolling slab made of an aluminum alloy with the composition, in weight %, Zn: 4.5-7.0; Mg: 1.2-3.5; Cu: 1.0-3.0; at least one element selected from among Cr: 0.04-0.35, Zr: 0.04-0.15 and Mn 0.04-0.5; Ti<0.25; Fe<0.6; Si<0.5; other elements <0.05 each and <0.15 in total, the remainder being aluminum,

[0009] b) homogenizing said rolling slab,

[0010] c) hot-rolling said rolling slab to obtain a plate with a thickness at least equal to 8 mm, the reduction rate upon the last hot-rolling pass being at most 20%,

[0011] d) carrying out an intermediate heat treatment lasting at least 1 hour at a temperature between 100° C. and 350° C.,

[0012] e) cold-rolling the heat treated plate with a reduction rate of 10% to 33%,

[0013] f) carrying out a solution heat treatment of the cold-rolled plate and quenching it,

[0014] g) stress relieving said solution heat treated and quenched plate by controlled stretching with a permanent elongation of 1 to 5%,

[0015] h) carrying out an aging of the solution heat treated, quenched and optionally stress relieved plate,

[0016] i) optionally, machining said aged plate to obtain a plate with a final thickness at least equal to 6 mm.

[0017] A second object of the invention is a plate with a thickness comprised between 6 and 25 mm made of an aluminum alloy with a composition, in weight %, Zn: 4.5-7.0; Mg: 1.2-3.5; Cu: 1.0-3.0; at least one element selected from among Cr: 0.04-0.35, Zr: 0.04-0.15 and Mn 0.04-0.5; Ti<0.25; Fe<0.6; Si<0.5; other elements <0.05 each and <0.15 in total, the remainder being aluminum, obtainable by the method according to the invention.

[0018] Another object of the invention is the use of a plate according to the invention as a precision plate, in particular for making machine elements, for example assembly or control tooling.FIGURES

[0019] FIG. 1 shows the granular structure in L / ST section in the final temper T651 of the product of Example 1.

[0020] FIG. 2 shows the granular structure in L / ST section in the final temper T651 of the product of Example 3.

[0021] FIG. 3 shows the steps performed for measuring deflection deviations. FIG. 3A: initial measurement of the deflection of the bar; FIG. 3B machining to remove % of the thickness,

[0022] FIG. 3C second measurement.DETAILED DESCRIPTION OF THE INVENTION

[0023] The designation of the alloys is done in accordance with the regulations of The Aluminum Association (AA), known to a person skilled in the art. The definitions of the metallurgical tempers are indicated in the European standard EN 515. Unless stated otherwise, the definitions of the standard EN12258-1 apply.

[0024] Unless stated otherwise, the compositions are expressed in weight %.

[0025] Unless stated otherwise, the static mechanical characteristics, in other words, the ultimate tensile strength Rm, the tensile yield strength at a 0.2% elongation Rp0.2 and the elongation at break A %, are determined by a tensile test according to the standard ISO 6892-1, the sampling and the direction of the test being defined by the standard EN 485-1.

[0026] According to the invention, improved plates made of an aluminum alloy of the 7XXX series, in particular precision plates, having an excellent flatness, an improved dimensional stability in particular during the machining steps, while having sufficient static mechanical properties, and a good anodization capability, are obtained thanks to a manufacturing method wherein, in particular the hot-rolling, intermediate heat treatment and cold-rolling steps are accurately controlled.

[0027] The manufacturing method according to the invention comprises casting, homogenization, hot-rolling, heat treatment and cold-rolling, solution heat treatment, quenching, stress relieving, aging and optionally machining steps.

[0028] In a first step, a rolling slab is cast made of an aluminum alloy with a composition, in weight %, Zn: 4.5-7.0; Mg: 1.2-3.5; Cu: 1.0-3.0; at least one element selected from among Cr: 0.04-0.35, Zr: 0.04-0.15 and Mn 0.04-0.5; Ti<0.25; Fe<0.6; Si<0.5; other elements <0.05 each and <0.15 in total, the remainder being aluminum, preferably by direct cooling vertical semi-continuous casting. The slab thus obtained may be scalped, i.e. machined, before the subsequent steps. Afterwards, the rolling slab is homogenized. Preferably, the homogenization temperature is at most 500° C. In an advantageous embodiment of the invention, the homogenization temperature is comprised between 450° C. and 500° C., preferably between 460° C. and 490° C. The homogenization duration is typically sufficient for the diffusion of the elements, typically at least 3 hours and preferably at least 5 hours. The maximum homogenization duration is typically 40 hours or 50 hours. Afterwards, hot-rolling is carried out to obtain a plate with a thickness at least equal to 8 mm and preferably at least equal to 10 mm, either directly after homogenization or after cooling and reheating up to a temperature typically of at least 340° C., preferably at least 370° C. and preferably at least 380° C. Preferably, the hot-rolling temperature is maintained at least at 300° C., preferably at least 310° C. and preferably at least 320° C. or even at least 330° C. Preferably, the temperature at the beginning of hot-rolling is at most 450° C. and preferably at most 420° C. Preferably, the hot-rolling exit temperature is at most 355° C., preferably at most 350° C. and preferably at most 345° C. Preferably, the rolling speed during the last hot-rolling pas sis at most 1,000 mm / s, preferably at most 900 mm / s and preferably at most 800 mm / s. The reduction rate during the last hot-rolling pass is at most 20%, preferably at most 19% and even more preferably at most 18%, or even more preferably at most 17%. When the reduction rate of the last hot-rolling pass is too high, in combination with the other parameters of the method, it is not possible to reach the desirable dimensional stability properties during machining. The combination of the composition, the homogenization and the hot-rolling conditions allows obtaining a structure that is essentially non-recrystallized, across the entire thickness of the hot-rolling raw product. By “essentially non-recrystallized across the entire thickness”, it should be understood that, irrespective of the position across the thickness, the recrystallization ratio is lower than 20% and preferably lower than 10%.

[0029] Afterwards, an intermediate heat treatment, allowing in particular recovering the hot-rolled plate is carried out, lasting at least 1 hour at a temperature between 100° C. and 350° C., advantageously at a temperature comprised between 130° C. and 320° C. and preferably at a temperature comprised between 200° C. and 300° C. It is the entire intermediate heat treatment, which may include one or more step(s) having different durations and temperatures, whose duration is at least 1 hour and whose temperature is between 100° C. and 350° C. Cold-rolling with a reduction rate of 10% to 33% is carried out after the intermediate heat treatment. Preferably, the cold-rolling reduction rate is 20% to 30%.

[0030] Afterwards, the hot-rolled, heat-treated and cold-rolled plate undergoes a solution heat treatment followed by quenching. Preferably, the solution heat treatment is performed at a temperature comprised between 450° C. and 500° C., preferably between 460° C. and 490° C. Quenching is typically carried out by immersion or spraying cold water. Afterwards, said solution-treated and quenched plate is stress-relieved by controlled stretching with a permanent elongation of 1 to 5%, preferably from 1.5 to 3%.

[0031] Finally, aging is carried out, typically at a temperature comprised between 100° C. and 170° C., preferably between 110° C. and 160° C. preferably to obtain a T6, T651 or T7 or T7X51 temper.

[0032] In one embodiment, said aged plate is finally machined to obtain a plate with a final thickness at least equal to 6 mm and preferably at least equal to 8 mm. Advantageously, at least 1 mm per face, preferably at least 1.5 mm per face or preferably at least 2 mm per face are machined so as to obtain a precision plate. An excessive machining, typically more than 5 mm per face is disadvantageous, in particular because of metal losses.

[0033] In particular, the method according to the invention allows obtaining a low deformation upon machining of the products. The method and the composition according to the invention allow obtaining a metallurgical structure, i.e. in particular a recrystallization ratio, a grain size and a texture, that is more homogeneous across the thickness of the product which promotes the machining capability.

[0034] The composition of the products according to the invention is selected so as to obtain, in combination with the thermomechanical treatment, the desired metallurgical structure.

[0035] The presence of at least one anti-recrystallizing element selected from among Cr: 0.04-0.35, Zr: 0.04-0.15 and Mn 0.04-0.5 is necessary. Cr is the anti-recrystallizing element that is preferred in the context 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 an embodiment of the invention, the Cr content is comprised between 0.18 and 0.28 weight % and the Zr and Mn contents are lower than 0.04 weight %, and are preferably lower than 0.03 weight %. In another embodiment of the invention, the Cr content is comprised between 0.18 and 0.28 weight %, the Zr content is lower than 0.04 weight %, and preferably lower than 0.03 weight %, and the Mn content is comprised between 0.04 and 0.30 weight %. In another embodiment of the invention, the Zr content is comprised between 0.06 and 0.15 weight %, the Cr content is lower than 0.05 weight % and the Mn content is comprised between 0.04 and 0.30 weight %. In another embodiment of the invention, the Zr content is comprised between 0.06 and 0.15 weight % and the Cr and Mn contents are lower than 0.04 weight % and preferably lower than 0.03 weight %.

[0036] Zn, Mg and Cu are added to reach the desired mechanical characteristics.

[0037] The Zn content is comprised between 4.5 and 7.0 weight %. Preferably, the minimum Zn content is 4.6%, advantageously 4.8% and preferably 5.1%. Preferably, the maximum Zn content is 6.8%, advantageously 6.6% and preferably 6.4% or even 6.1%. In an embodiment of the invention, the Zn content is comprised between 5.2 and 6.0 weight %.

[0038] The Mg content is comprised between 1.2 and 3.5 weight %. Preferably, the minimum Mg content is 1.5%, advantageously 1.8% and preferably 2.1%. Preferably, the maximum Mg content is 3.3%, advantageously 3.1% and preferably 3.0% or even 2.9%. In an embodiment of the invention, the Mg content is comprised between 2.2 and 2.8 weight %.

[0039] The Cu content is comprised between 1.0 and 3.0 weight %. Preferably, the minimum Cu content is 1.1%, advantageously 1.2% and preferably 1.3%. Preferably, the maximum Cu content is 2.8%, advantageously 2.6% and preferably 2.3% or even 2.0%. In an embodiment of the invention, the Cu content is comprised between 1.3 and 1.9 weight %. Preferably, the Mg content is higher than the Cu content and preferably Mg / Cu is higher than 1.1 and even more preferably higher than 1.2 or even 1.3.

[0040] The Ti content is lower than 0.25 weight %. It may be advantageous to add Ti, in particular for controlling the grain size during casting. In an embodiment of the invention, the Ti content is comprised between 0.01 and 0.20 weight %.

[0041] The iron content is lower than 0.6 weight %. Preferably, the maximum Fe content is 0.50%, advantageously 0.35% and preferably 0.15%. Preferably, the minimum Fe content is 0.05%, advantageously, 0.10% and preferably 0.15%.

[0042] The silicon content is lower than 0.5 weight %. Preferably, the maximum Si content is 0.45%, advantageously 0.40% and preferably 0.35%. Preferably, the minimum Si content is 0.05%, advantageously 0.10% and preferably 0.15%.

[0043] The other elements may be present as unavoidable impurities with a content lower than 0.05 weight % each, preferably lower than 0.04 weight % and preferably lower than 0.03 weight % and lower than 0.15 weight % in total, and preferably lower than 0.10 weight % in total, the remainder is aluminum.

[0044] The plates that could be obtained by the method according to the invention have particularly advantageous properties.

[0045] The mechanical properties of the metal sheets according to the invention are particularly advantageous. Preferably, the plates according to the invention have a tensile yield strength Rp0.2LT of at least 450 MPa, preferably at least 460 MPa and preferably at least 480 MPa, and / or an ultimate tensile strength RmLT of at least 500 MPa, preferably at least 520 MPa and preferably at least 540 MPa and / or an elongation at break A % of at least 6%, preferably at least 8% and preferably at least 10%.

[0046] The plates according to the invention typically have a low level of internal stresses. Thus, advantageously, the product of the maximum deflection deviation in the directions L and LT multiplied by the final thickness after machining is at most 3 and preferably at most 2. The considered deflection deviations to obtain the value of the maximum deflection deviation are, in absolute value, on the one hand, the deflection deviation between the deflection measured for a bar with the dimension 400 mm×30 mm×thickness at the exit of cold-rolling and the deflection measured for this same bar after machining 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 M of the thickness with respect to the thickness at the exit of cold-rolling, and the deflection measured for this previous bar after an additional machining of M of its thickness, all deflection measurements being performed with the bar placed on two supports distant apart by 390 mm and the deflections being expressed in mm, all measurements being performed after aging and before the final optional machining step and in the two directions L and LT.

[0047] The texture of the products according to the invention is also advantageous. The crystallographic texture may be described by a 3-dimensional mathematical function. This function is known in the art as the Orientation Distribution Function (ODF). It is defined as the volumetric fraction of the material dV / V having an orientation g within a dg margin:dV / Vdg=f⁡(g)=f⁡(φ1,Φ,φ2)

[0048] where (ϕ1, Φ, ϕ2) are the Euler angles describing the orientation g.

[0049] The ODF of each plate is measured by the spherical harmonics method from four pole figures measured by X-ray diffraction on a conventional texture goniometer. In the context of the invention, the measurements of the pole figures have been carried out on samples cut at the mid-thickness of the plates.

[0050] The information contained in the ODF has been simplified, as known to a person skilled in the art, in order to describe the texture as a proportion of grains contained in a discretized Euler space.

[0051] The volumetric fractions of the different texture components have been combined into two categories: the planar compression texture components: Copper {112}<111>, Brass {110}<112> and S {123}<634> and the shear texture components I {112}<110>, J {114}<110>, GT90DN {011}<0-11>, H {001}<1-10> and Z {111}<110>. In particular, we have studied the sum of the volumetric fraction of each of these categories as a function of the position across the thickness.

[0052] The plates according to the invention typically have a balanced texture between planar compression and shear irrespective of the position across the thickness, advantageously the ratio of the sum of the planar compression texture volumetric fraction to the sum of the shear texture volumetric fraction comprised between 0.5 and 1.5 and preferably between 0.6 and 1.3 between the mid-thickness and the final surface after machining if a machining has been carried out or 1.5 mm under the surface if no machining has been carried out. As regards the plates according to the prior art, this ratio reaches values substantially higher than 1.5 at some positions across the thickness, in particular at the surface.

[0053] According to the invention, plates according to the invention are used as precision plates, in particular to make machine bases, reference plates, transport tables, assembly jigs, robot arms or parts with a complex shape with a lot of material removal after machining, typically in which at least 30%, and possibly 50%, of the material have been removed. Indeed, the plates according to the invention have an improved dimensional stability in particular during the machining steps, while having sufficient static mechanical properties, and a good anodization capability.Example

[0054] In this example, we have prepared rolling slabs made of an AA7075 alloy whose composition is given in Table 1.TABLE 1ExampleZnMgCuCrZrMnTiFeSi15.92.51.40.180.020.040.030.140.0825.82.41.40.190.020.040.030.150.0935.82.51.40.180.010.050.030.160.0845.72.41.50.190.020.060.030.170.1055.82.51.50.190.020.050.030.160.0965.92.51.50.190.020.060.030.170.1075.82.51.50.190.010.050.030.170.0985.82.51.50.190.010.050.030.170.0995.92.51.40.190.020.040.030.140.08Composition of the Alloys in Percentage by Weight

[0055] The slabs have been homogenized at 480° C. and hot-rolled down to a thickness indicated in Table 2. The hot-rolling entry temperature was comprised between 38° and 410° C. The Examples 1, 2, 5, 8 and 9 have been transformed with a method that is not covered by the invention. As regards the plates 1, 2 and 5, a reference method has been applied wherein the reduction during the last pass has been at least 21% and for which the intermediate heat treatment has been performed in two successive steps at 410° C. and then at 300° C. As regards Example 8, the hot-rolling and intermediate heat treatment conditions were according to the invention, but the cold-rolling reduction rate was higher than 33%. As regards Example 9, the intermediate heat treatment has been performed at 250° C. but the temperature at the end of hot-rolling has been kept at a value higher than 355° C. and the reduction during the last pass was 21%.TABLE 2Speed atTemperaturethe lastFinalat the endReduction %hot-Hot-rollingCold-rollingmachiningof the lastof the lastrollingIntermediateReduction %exitexitexitrolling passhot-rollingpassheatof thethicknessthicknessthicknessExample(° C.)pass(mm / s)treatmentcold-rolling(mm)(mm)(mm)1359251100410° C. / 5 h +2514.8118300° C. / 2 h2372251100410° C. / 5 h +2520.21512300° C. / 2 h333817670250° C. / 2 h2517.51310434517900250° C. / 2 h2520.215125375211100410° C. / 5 h +2531.02320300° C. / 2 h634315880250° C. / 2 h2531.02320734013670250° C. / 2 h2531.02320833515670250° C. / 2 h3520.213109360211122250° C. / 2 h2517.61310

[0056] The plates thus obtained have been solution heat treated at 475° C., quenched, stress-relieved by controlled stretching and aged to obtain a T651 temper. The aging conditions were 9 hours at 140° C. At a last step, a machining of 3 mm (1.5 mm per face) has been performed so that the final thickness was smaller by 3 mm than the thickness at the end of rolling.

[0057] The tensile static mechanical characteristics, in other words the ultimate tensile strength Rm, the tensile yield strength at 0.2% elongation Rp0.2 and the elongation at break A %, have been determined by a tensile test according to the standard NF EN ISO 6892-1 (2016) in the long transverse direction (LT), the sampling and the direction of the test being defined by the standard EN 485 (2016). Sampling is carried out before the last machining step. The characterizations have been performed in the long transverse direction.

[0058] The results are given in Table 3.TABLE 3Rp0.2 LTRm LTExampleMPaMPaA %456449213.9556750011.6656850011.8757550812.4857450413.3958651413.1Static Mechanical Properties

[0059] The residual stresses have been assessed on the plate before machining by measuring the average deflection on bars machined in the direction L or LT at ¼ and at ½ of thickness.

[0060] Two full-thickness bars are sampled, in the direction Land LT, by sawing the plate before final machining. The sampling dimensions are:

[0061] for the L direction bar: 430 mm (direction L)×35 mm (direction LT)×thickness

[0062] for the LT direction bar: 450 mm (direction LT)×35 mm (direction L)×thickness.

[0063] Afterwards, the bars are machined to obtain a bar with a length L=400 mm and with a width I=30 mm and with a thickness e (thickness of the plate after cold-rolling and aging but before machining). The rolling raw L-LT faces are not machined so that the thickness of the machined bars remains the thickness of the plate.

[0064] As regards the deflection measurements, the bar is placed on two supports spaced apart by 390 mm (the supports are represented by triangles 1 in FIG. 3-A). A displacement sensor (represented by an arrow 22FIG. 3A) is used to measure the deflection of the bar.

[0065] The steps are as follows:

[0066] An initial measurement of the deflection of the bar is carried out (cf. FIG. 3A), which gives the values referenced Deflection L ini and Deflection LT ini expressed in mm.

[0067] Afterwards, the bar is machined to remove ¼ of its thickness (cf. diagram FIG. 3 B).

[0068] A second measurement is performed (cf. FIG. 3 C) which gives the values referenced Deflection L ¼ and Deflection LT ¼ expressed in mm.

[0069] The bar is machined again to remove ¼ more of its thickness. Then, only half of the initial thickness remains

[0070] A third measurement is performed which gives the values referenced Deflection L ½ and Deflection LT ½ expressed in mm.

[0071] In each machining step, the heat-up is limited to 10° C. so as to avoid any influence of the machining conditions on the performed deflection measurements.

[0072] The deflection deviations, in absolute value (Abs), between % and initial and then between ½ and ¼ are reported in Table 4 hereinbelow, for the directions L and LT. The maximum deflection deviation multiplied by the thickness at the exit of rolling is also reported.TABLE 4Deflection deviations (mm)AbsAbsAbsAbsMaximumFinal(Deflection(Deflection(Deflection(Deflectiondeflectionthick-L ¼−L ½−LT ¼−LT ½−Maxdeviation ×nessDeflectionDeflectionDeflectionDeflectionabsolutefinalExample(mm)L ini)L 1 / 4)LT ini)LT 1 / 4)valuethickness180.510.480.130.190.514.12120.340.30.120.130.344.13100.130.120.070.080.131.34120.10.250.140.240.253.05200.180.160.050.080.183.66200.010.090.040.080.091.87200.0080.020.010.040.040.88100.330.060.130.120.333.39100.220.530.060.0360.535.3Deflections Measured on Machined Bars

[0073] With the reference method, the product of the maximum deflection deviation in the directions L and LT multiplied by the final thickness is greater than 3.2; whereas with the method according to the invention, this product is at most 3.0.

[0074] The final granular structure has been characterized after cold-rolling and aging. The results are depicted in FIGS. 1 and 2. FIG. 1 shows the granular structure after anodic oxidation of the plate 1 after the reference method. FIG. 2 shows the granular structure after anodic oxidation of the plate 3 after the method according to the invention. In FIG. 1, one could observe a microstructure that is essentially recrystallized close to the surfaces and a mixed recrystallized / non-recrystallized microstructure at mid-thickness. There are significant grain size heterogeneities. In FIG. 2, one could also observe more recrystallization at the surface with a much more homogeneous grain size.

[0075] The texture of the products has been measured on 50×50 mm samples in the L / LT plane, at mid-thickness and at the surface (between 0.1 and 0.4 mm under the surface after machining). The results are reported in Table 5. As regards the product according to the invention, the texture at the milled surface is closer to the texture at mid-thickness and more balanced between shear and compression than is the case for the reference product.TABLE 5Mid-thicknessSurfaceSum of theSum of theplanarSum of theplanarSum of thecompressionshearcompressionshearcomponentscomponentscomponentscomponentsin % byin % byCompression / in % byin % byCompression / Examplevolumevolumeshear ratiovolumevolumeshear ratio121.920.11.132.57.44.4324.420.11.213.820.10.7

Examples

example

[0054]In this example, we have prepared rolling slabs made of an AA7075 alloy whose composition is given in Table 1.

TABLE 1ExampleZnMgCuCrZrMnTiFeSi15.92.51.40.180.020.040.030.140.0825.82.41.40.190.020.040.030.150.0935.82.51.40.180.010.050.030.160.0845.72.41.50.190.020.060.030.170.1055.82.51.50.190.020.050.030.160.0965.92.51.50.190.020.060.030.170.1075.82.51.50.190.010.050.030.170.0985.82.51.50.190.010.050.030.170.0995.92.51.40.190.020.040.030.140.08

Composition of the Alloys in Percentage by Weight

[0055]The slabs have been homogenized at 480° C. and hot-rolled down to a thickness indicated in Table 2. The hot-rolling entry temperature was comprised between 38° and 410° C. The Examples 1, 2, 5, 8 and 9 have been transformed with a method that is not covered by the invention. As regards the plates 1, 2 and 5, a reference method has been applied wherein the reduction during the last pass has been at least 21% and for which the intermediate heat treatment has been performed in two succe...

TECHNICAL FIELD

[0001] The invention relates to plates made of an aluminum alloy of the 7xxx series, intended in particular to be used as a precision plate.PRIOR ART

[0002] An excellent dimensional stability is very important for applications involving precision plates, whose thickness is typically comprised between 6 and 150 mm. This product type is typically used for making machine elements, in particular as reference plates for assembly or control tooling. For these applications, it is particularly important to reduce as much as possible any deformation of the plate during machining thereof, which allows avoiding additional pre-machining or final finishing operations.

[0003] Precision plates made of a 6xxx alloy are known, in particular from the application WO2021 / 064320 which discloses plates with a thickness comprised between 8 and 50 mm lade of an aluminum allow with a composition, in 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 among 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 being aluminum. These precision plates are particularly useful as precision plates, in particular for making machine elements, for example assembly or control tooling.

[0004] Moreover, the precision plates ALPLAN©7075 are known which combine a good dimensional stability with a high mechanical strength as well as a good flatness and a low roughness of the surfaces (cf.

[0005] https: / / www.constellium.com / sites / default / files / tid_product_documents / alplan_7075.pdf).

[0006] There is a need for improved plates made of an aluminum alloy of the 7XXX series, in particular precision plates, having an improved dimensional stability in particular during the machining steps, while having sufficient static mechanical properties, and an excellent anodization capability.DISCLOSURE OF THE INVENTION

[0007] A first object of the invention is a method for manufacturing a plate made of an aluminum alloy with a final thickness comprised between 6 and 25 mm, wherein, successively,

[0008] a) casting a rolling slab made of an aluminum alloy with the composition, in weight %, Zn: 4.5-7.0; Mg: 1.2-3.5; Cu: 1.0-3.0; at least one element selected from among Cr: 0.04-0.35, Zr: 0.04-0.15 and Mn 0.04-0.5; Ti<0.25; Fe<0.6; Si<0.5; other elements <0.05 each and <0.15 in total, the remainder being aluminum,

[0009] b) homogenizing said rolling slab,

[0010] c) hot-rolling said rolling slab to obtain a plate with a thickness at least equal to 8 mm, the reduction rate upon the last hot-rolling pass being at most 20%,

[0011] d) carrying out an intermediate heat treatment lasting at least 1 hour at a temperature between 100° C. and 350° C.,

[0012] e) cold-rolling the heat treated plate with a reduction rate of 10% to 33%,

[0013] f) carrying out a solution heat treatment of the cold-rolled plate and quenching it,

[0014] g) stress relieving said solution heat treated and quenched plate by controlled stretching with a permanent elongation of 1 to 5%,

[0015] h) carrying out an aging of the solution heat treated, quenched and optionally stress relieved plate,

[0016] i) optionally, machining said aged plate to obtain a plate with a final thickness at least equal to 6 mm.

[0017] A second object of the invention is a plate with a thickness comprised between 6 and 25 mm made of an aluminum alloy with a composition, in weight %, Zn: 4.5-7.0; Mg: 1.2-3.5; Cu: 1.0-3.0; at least one element selected from among Cr: 0.04-0.35, Zr: 0.04-0.15 and Mn 0.04-0.5; Ti<0.25; Fe<0.6; Si<0.5; other elements <0.05 each and <0.15 in total, the remainder being aluminum, obtainable by the method according to the invention.

[0018] Another object of the invention is the use of a plate according to the invention as a precision plate, in particular for making machine elements, for example assembly or control tooling.FIGURES

[0019] FIG. 1 shows the granular structure in L / ST section in the final temper T651 of the product of Example 1.

[0020] FIG. 2 shows the granular structure in L / ST section in the final temper T651 of the product of Example 3.

[0021] FIG. 3 shows the steps performed for measuring deflection deviations. FIG. 3A: initial measurement of the deflection of the bar; FIG. 3B machining to remove % of the thickness,

[0022] FIG. 3C second measurement.DETAILED DESCRIPTION OF THE INVENTION

[0023] The designation of the alloys is done in accordance with the regulations of The Aluminum Association (AA), known to a person skilled in the art. The definitions of the metallurgical tempers are indicated in the European standard EN 515. Unless stated otherwise, the definitions of the standard EN12258-1 apply.

[0024] Unless stated otherwise, the compositions are expressed in weight %.

[0025] Unless stated otherwise, the static mechanical characteristics, in other words, the ultimate tensile strength Rm, the tensile yield strength at a 0.2% elongation Rp0.2 and the elongation at break A %, are determined by a tensile test according to the standard ISO 6892-1, the sampling and the direction of the test being defined by the standard EN 485-1.

[0026] According to the invention, improved plates made of an aluminum alloy of the 7XXX series, in particular precision plates, having an excellent flatness, an improved dimensional stability in particular during the machining steps, while having sufficient static mechanical properties, and a good anodization capability, are obtained thanks to a manufacturing method wherein, in particular the hot-rolling, intermediate heat treatment and cold-rolling steps are accurately controlled.

[0027] The manufacturing method according to the invention comprises casting, homogenization, hot-rolling, heat treatment and cold-rolling, solution heat treatment, quenching, stress relieving, aging and optionally machining steps.

[0028] In a first step, a rolling slab is cast made of an aluminum alloy with a composition, in weight %, Zn: 4.5-7.0; Mg: 1.2-3.5; Cu: 1.0-3.0; at least one element selected from among Cr: 0.04-0.35, Zr: 0.04-0.15 and Mn 0.04-0.5; Ti<0.25; Fe<0.6; Si<0.5; other elements <0.05 each and <0.15 in total, the remainder being aluminum, preferably by direct cooling vertical semi-continuous casting. The slab thus obtained may be scalped, i.e. machined, before the subsequent steps. Afterwards, the rolling slab is homogenized. Preferably, the homogenization temperature is at most 500° C. In an advantageous embodiment of the invention, the homogenization temperature is comprised between 450° C. and 500° C., preferably between 460° C. and 490° C. The homogenization duration is typically sufficient for the diffusion of the elements, typically at least 3 hours and preferably at least 5 hours. The maximum homogenization duration is typically 40 hours or 50 hours. Afterwards, hot-rolling is carried out to obtain a plate with a thickness at least equal to 8 mm and preferably at least equal to 10 mm, either directly after homogenization or after cooling and reheating up to a temperature typically of at least 340° C., preferably at least 370° C. and preferably at least 380° C. Preferably, the hot-rolling temperature is maintained at least at 300° C., preferably at least 310° C. and preferably at least 320° C. or even at least 330° C. Preferably, the temperature at the beginning of hot-rolling is at most 450° C. and preferably at most 420° C. Preferably, the hot-rolling exit temperature is at most 355° C., preferably at most 350° C. and preferably at most 345° C. Preferably, the rolling speed during the last hot-rolling pas sis at most 1,000 mm / s, preferably at most 900 mm / s and preferably at most 800 mm / s. The reduction rate during the last hot-rolling pass is at most 20%, preferably at most 19% and even more preferably at most 18%, or even more preferably at most 17%. When the reduction rate of the last hot-rolling pass is too high, in combination with the other parameters of the method, it is not possible to reach the desirable dimensional stability properties during machining. The combination of the composition, the homogenization and the hot-rolling conditions allows obtaining a structure that is essentially non-recrystallized, across the entire thickness of the hot-rolling raw product. By “essentially non-recrystallized across the entire thickness”, it should be understood that, irrespective of the position across the thickness, the recrystallization ratio is lower than 20% and preferably lower than 10%.

[0029] Afterwards, an intermediate heat treatment, allowing in particular recovering the hot-rolled plate is carried out, lasting at least 1 hour at a temperature between 100° C. and 350° C., advantageously at a temperature comprised between 130° C. and 320° C. and preferably at a temperature comprised between 200° C. and 300° C. It is the entire intermediate heat treatment, which may include one or more step(s) having different durations and temperatures, whose duration is at least 1 hour and whose temperature is between 100° C. and 350° C. Cold-rolling with a reduction rate of 10% to 33% is carried out after the intermediate heat treatment. Preferably, the cold-rolling reduction rate is 20% to 30%.

[0030] Afterwards, the hot-rolled, heat-treated and cold-rolled plate undergoes a solution heat treatment followed by quenching. Preferably, the solution heat treatment is performed at a temperature comprised between 450° C. and 500° C., preferably between 460° C. and 490° C. Quenching is typically carried out by immersion or spraying cold water. Afterwards, said solution-treated and quenched plate is stress-relieved by controlled stretching with a permanent elongation of 1 to 5%, preferably from 1.5 to 3%.

[0031] Finally, aging is carried out, typically at a temperature comprised between 100° C. and 170° C., preferably between 110° C. and 160° C. preferably to obtain a T6, T651 or T7 or T7X51 temper.

[0032] In one embodiment, said aged plate is finally machined to obtain a plate with a final thickness at least equal to 6 mm and preferably at least equal to 8 mm. Advantageously, at least 1 mm per face, preferably at least 1.5 mm per face or preferably at least 2 mm per face are machined so as to obtain a precision plate. An excessive machining, typically more than 5 mm per face is disadvantageous, in particular because of metal losses.

[0033] In particular, the method according to the invention allows obtaining a low deformation upon machining of the products. The method and the composition according to the invention allow obtaining a metallurgical structure, i.e. in particular a recrystallization ratio, a grain size and a texture, that is more homogeneous across the thickness of the product which promotes the machining capability.

[0034] The composition of the products according to the invention is selected so as to obtain, in combination with the thermomechanical treatment, the desired metallurgical structure.

[0035] The presence of at least one anti-recrystallizing element selected from among Cr: 0.04-0.35, Zr: 0.04-0.15 and Mn 0.04-0.5 is necessary. Cr is the anti-recrystallizing element that is preferred in the context 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 an embodiment of the invention, the Cr content is comprised between 0.18 and 0.28 weight % and the Zr and Mn contents are lower than 0.04 weight %, and are preferably lower than 0.03 weight %. In another embodiment of the invention, the Cr content is comprised between 0.18 and 0.28 weight %, the Zr content is lower than 0.04 weight %, and preferably lower than 0.03 weight %, and the Mn content is comprised between 0.04 and 0.30 weight %. In another embodiment of the invention, the Zr content is comprised between 0.06 and 0.15 weight %, the Cr content is lower than 0.05 weight % and the Mn content is comprised between 0.04 and 0.30 weight %. In another embodiment of the invention, the Zr content is comprised between 0.06 and 0.15 weight % and the Cr and Mn contents are lower than 0.04 weight % and preferably lower than 0.03 weight %.

[0036] Zn, Mg and Cu are added to reach the desired mechanical characteristics.

[0037] The Zn content is comprised between 4.5 and 7.0 weight %. Preferably, the minimum Zn content is 4.6%, advantageously 4.8% and preferably 5.1%. Preferably, the maximum Zn content is 6.8%, advantageously 6.6% and preferably 6.4% or even 6.1%. In an embodiment of the invention, the Zn content is comprised between 5.2 and 6.0 weight %.

[0038] The Mg content is comprised between 1.2 and 3.5 weight %. Preferably, the minimum Mg content is 1.5%, advantageously 1.8% and preferably 2.1%. Preferably, the maximum Mg content is 3.3%, advantageously 3.1% and preferably 3.0% or even 2.9%. In an embodiment of the invention, the Mg content is comprised between 2.2 and 2.8 weight %.

[0039] The Cu content is comprised between 1.0 and 3.0 weight %. Preferably, the minimum Cu content is 1.1%, advantageously 1.2% and preferably 1.3%. Preferably, the maximum Cu content is 2.8%, advantageously 2.6% and preferably 2.3% or even 2.0%. In an embodiment of the invention, the Cu content is comprised between 1.3 and 1.9 weight %. Preferably, the Mg content is higher than the Cu content and preferably Mg / Cu is higher than 1.1 and even more preferably higher than 1.2 or even 1.3.

[0040] The Ti content is lower than 0.25 weight %. It may be advantageous to add Ti, in particular for controlling the grain size during casting. In an embodiment of the invention, the Ti content is comprised between 0.01 and 0.20 weight %.

[0041] The iron content is lower than 0.6 weight %. Preferably, the maximum Fe content is 0.50%, advantageously 0.35% and preferably 0.15%. Preferably, the minimum Fe content is 0.05%, advantageously, 0.10% and preferably 0.15%.

[0042] The silicon content is lower than 0.5 weight %. Preferably, the maximum Si content is 0.45%, advantageously 0.40% and preferably 0.35%. Preferably, the minimum Si content is 0.05%, advantageously 0.10% and preferably 0.15%.

[0043] The other elements may be present as unavoidable impurities with a content lower than 0.05 weight % each, preferably lower than 0.04 weight % and preferably lower than 0.03 weight % and lower than 0.15 weight % in total, and preferably lower than 0.10 weight % in total, the remainder is aluminum.

[0044] The plates that could be obtained by the method according to the invention have particularly advantageous properties.

[0045] The mechanical properties of the metal sheets according to the invention are particularly advantageous. Preferably, the plates according to the invention have a tensile yield strength Rp0.2LT of at least 450 MPa, preferably at least 460 MPa and preferably at least 480 MPa, and / or an ultimate tensile strength RmLT of at least 500 MPa, preferably at least 520 MPa and preferably at least 540 MPa and / or an elongation at break A % of at least 6%, preferably at least 8% and preferably at least 10%.

[0046] The plates according to the invention typically have a low level of internal stresses. Thus, advantageously, the product of the maximum deflection deviation in the directions L and LT multiplied by the final thickness after machining is at most 3 and preferably at most 2. The considered deflection deviations to obtain the value of the maximum deflection deviation are, in absolute value, on the one hand, the deflection deviation between the deflection measured for a bar with the dimension 400 mm×30 mm×thickness at the exit of cold-rolling and the deflection measured for this same bar after machining 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 M of the thickness with respect to the thickness at the exit of cold-rolling, and the deflection measured for this previous bar after an additional machining of M of its thickness, all deflection measurements being performed with the bar placed on two supports distant apart by 390 mm and the deflections being expressed in mm, all measurements being performed after aging and before the final optional machining step and in the two directions L and LT.

[0047] The texture of the products according to the invention is also advantageous. The crystallographic texture may be described by a 3-dimensional mathematical function. This function is known in the art as the Orientation Distribution Function (ODF). It is defined as the volumetric fraction of the material dV / V having an orientation g within a dg margin:dV / Vdg=f⁡(g)=f⁡(φ1,Φ,φ2)

[0048] where (ϕ1, Φ, ϕ2) are the Euler angles describing the orientation g.

[0049] The ODF of each plate is measured by the spherical harmonics method from four pole figures measured by X-ray diffraction on a conventional texture goniometer. In the context of the invention, the measurements of the pole figures have been carried out on samples cut at the mid-thickness of the plates.

[0050] The information contained in the ODF has been simplified, as known to a person skilled in the art, in order to describe the texture as a proportion of grains contained in a discretized Euler space.

[0051] The volumetric fractions of the different texture components have been combined into two categories: the planar compression texture components: Copper {112}<111>, Brass {110}<112> and S {123}<634> and the shear texture components I {112}<110>, J {114}<110>, GT90DN {011}<0-11>, H {001}<1-10> and Z {111}<110>. In particular, we have studied the sum of the volumetric fraction of each of these categories as a function of the position across the thickness.

[0052] The plates according to the invention typically have a balanced texture between planar compression and shear irrespective of the position across the thickness, advantageously the ratio of the sum of the planar compression texture volumetric fraction to the sum of the shear texture volumetric fraction comprised between 0.5 and 1.5 and preferably between 0.6 and 1.3 between the mid-thickness and the final surface after machining if a machining has been carried out or 1.5 mm under the surface if no machining has been carried out. As regards the plates according to the prior art, this ratio reaches values substantially higher than 1.5 at some positions across the thickness, in particular at the surface.

[0053] According to the invention, plates according to the invention are used as precision plates, in particular to make machine bases, reference plates, transport tables, assembly jigs, robot arms or parts with a complex shape with a lot of material removal after machining, typically in which at least 30%, and possibly 50%, of the material have been removed. Indeed, the plates according to the invention have an improved dimensional stability in particular during the machining steps, while having sufficient static mechanical properties, and a good anodization capability.Example

[0054] In this example, we have prepared rolling slabs made of an AA7075 alloy whose composition is given in Table 1.TABLE 1ExampleZnMgCuCrZrMnTiFeSi15.92.51.40.180.020.040.030.140.0825.82.41.40.190.020.040.030.150.0935.82.51.40.180.010.050.030.160.0845.72.41.50.190.020.060.030.170.1055.82.51.50.190.020.050.030.160.0965.92.51.50.190.020.060.030.170.1075.82.51.50.190.010.050.030.170.0985.82.51.50.190.010.050.030.170.0995.92.51.40.190.020.040.030.140.08Composition of the Alloys in Percentage by Weight

[0055] The slabs have been homogenized at 480° C. and hot-rolled down to a thickness indicated in Table 2. The hot-rolling entry temperature was comprised between 38° and 410° C. The Examples 1, 2, 5, 8 and 9 have been transformed with a method that is not covered by the invention. As regards the plates 1, 2 and 5, a reference method has been applied wherein the reduction during the last pass has been at least 21% and for which the intermediate heat treatment has been performed in two successive steps at 410° C. and then at 300° C. As regards Example 8, the hot-rolling and intermediate heat treatment conditions were according to the invention, but the cold-rolling reduction rate was higher than 33%. As regards Example 9, the intermediate heat treatment has been performed at 250° C. but the temperature at the end of hot-rolling has been kept at a value higher than 355° C. and the reduction during the last pass was 21%.TABLE 2Speed atTemperaturethe lastFinalat the endReduction %hot-Hot-rollingCold-rollingmachiningof the lastof the lastrollingIntermediateReduction %exitexitexitrolling passhot-rollingpassheatof thethicknessthicknessthicknessExample(° C.)pass(mm / s)treatmentcold-rolling(mm)(mm)(mm)1359251100410° C. / 5 h +2514.8118300° C. / 2 h2372251100410° C. / 5 h +2520.21512300° C. / 2 h333817670250° C. / 2 h2517.51310434517900250° C. / 2 h2520.215125375211100410° C. / 5 h +2531.02320300° C. / 2 h634315880250° C. / 2 h2531.02320734013670250° C. / 2 h2531.02320833515670250° C. / 2 h3520.213109360211122250° C. / 2 h2517.61310

[0056] The plates thus obtained have been solution heat treated at 475° C., quenched, stress-relieved by controlled stretching and aged to obtain a T651 temper. The aging conditions were 9 hours at 140° C. At a last step, a machining of 3 mm (1.5 mm per face) has been performed so that the final thickness was smaller by 3 mm than the thickness at the end of rolling.

[0057] The tensile static mechanical characteristics, in other words the ultimate tensile strength Rm, the tensile yield strength at 0.2% elongation Rp0.2 and the elongation at break A %, have been determined by a tensile test according to the standard NF EN ISO 6892-1 (2016) in the long transverse direction (LT), the sampling and the direction of the test being defined by the standard EN 485 (2016). Sampling is carried out before the last machining step. The characterizations have been performed in the long transverse direction.

[0058] The results are given in Table 3.TABLE 3Rp0.2 LTRm LTExampleMPaMPaA %456449213.9556750011.6656850011.8757550812.4857450413.3958651413.1Static Mechanical Properties

[0059] The residual stresses have been assessed on the plate before machining by measuring the average deflection on bars machined in the direction L or LT at ¼ and at ½ of thickness.

[0060] Two full-thickness bars are sampled, in the direction Land LT, by sawing the plate before final machining. The sampling dimensions are:

[0061] for the L direction bar: 430 mm (direction L)×35 mm (direction LT)×thickness

[0062] for the LT direction bar: 450 mm (direction LT)×35 mm (direction L)×thickness.

[0063] Afterwards, the bars are machined to obtain a bar with a length L=400 mm and with a width I=30 mm and with a thickness e (thickness of the plate after cold-rolling and aging but before machining). The rolling raw L-LT faces are not machined so that the thickness of the machined bars remains the thickness of the plate.

[0064] As regards the deflection measurements, the bar is placed on two supports spaced apart by 390 mm (the supports are represented by triangles 1 in FIG. 3-A). A displacement sensor (represented by an arrow 22FIG. 3A) is used to measure the deflection of the bar.

[0065] The steps are as follows:

[0066] An initial measurement of the deflection of the bar is carried out (cf. FIG. 3A), which gives the values referenced Deflection L ini and Deflection LT ini expressed in mm.

[0067] Afterwards, the bar is machined to remove ¼ of its thickness (cf. diagram FIG. 3 B).

[0068] A second measurement is performed (cf. FIG. 3 C) which gives the values referenced Deflection L ¼ and Deflection LT ¼ expressed in mm.

[0069] The bar is machined again to remove ¼ more of its thickness. Then, only half of the initial thickness remains

[0070] A third measurement is performed which gives the values referenced Deflection L ½ and Deflection LT ½ expressed in mm.

[0071] In each machining step, the heat-up is limited to 10° C. so as to avoid any influence of the machining conditions on the performed deflection measurements.

[0072] The deflection deviations, in absolute value (Abs), between % and initial and then between ½ and ¼ are reported in Table 4 hereinbelow, for the directions L and LT. The maximum deflection deviation multiplied by the thickness at the exit of rolling is also reported.TABLE 4Deflection deviations (mm)AbsAbsAbsAbsMaximumFinal(Deflection(Deflection(Deflection(Deflectiondeflectionthick-L ¼−L ½−LT ¼−LT ½−Maxdeviation ×nessDeflectionDeflectionDeflectionDeflectionabsolutefinalExample(mm)L ini)L 1 / 4)LT ini)LT 1 / 4)valuethickness180.510.480.130.190.514.12120.340.30.120.130.344.13100.130.120.070.080.131.34120.10.250.140.240.253.05200.180.160.050.080.183.66200.010.090.040.080.091.87200.0080.020.010.040.040.88100.330.060.130.120.333.39100.220.530.060.0360.535.3Deflections Measured on Machined Bars

[0073] With the reference method, the product of the maximum deflection deviation in the directions L and LT multiplied by the final thickness is greater than 3.2; whereas with the method according to the invention, this product is at most 3.0.

[0074] The final granular structure has been characterized after cold-rolling and aging. The results are depicted in FIGS. 1 and 2. FIG. 1 shows the granular structure after anodic oxidation of the plate 1 after the reference method. FIG. 2 shows the granular structure after anodic oxidation of the plate 3 after the method according to the invention. In FIG. 1, one could observe a microstructure that is essentially recrystallized close to the surfaces and a mixed recrystallized / non-recrystallized microstructure at mid-thickness. There are significant grain size heterogeneities. In FIG. 2, one could also observe more recrystallization at the surface with a much more homogeneous grain size.

[0075] The texture of the products has been measured on 50×50 mm samples in the L / LT plane, at mid-thickness and at the surface (between 0.1 and 0.4 mm under the surface after machining). The results are reported in Table 5. As regards the product according to the invention, the texture at the milled surface is closer to the texture at mid-thickness and more balanced between shear and compression than is the case for the reference product.TABLE 5Mid-thicknessSurfaceSum of theSum of theplanarSum of theplanarSum of thecompressionshearcompressionshearcomponentscomponentscomponentscomponentsin % byin % byCompression / in % byin % byCompression / Examplevolumevolumeshear ratiovolumevolumeshear ratio121.920.11.132.57.44.4324.420.11.213.820.10.7

Examples

example

[0054]In this example, we have prepared rolling slabs made of an AA7075 alloy whose composition is given in Table 1.

TABLE 1ExampleZnMgCuCrZrMnTiFeSi15.92.51.40.180.020.040.030.140.0825.82.41.40.190.020.040.030.150.0935.82.51.40.180.010.050.030.160.0845.72.41.50.190.020.060.030.170.1055.82.51.50.190.020.050.030.160.0965.92.51.50.190.020.060.030.170.1075.82.51.50.190.010.050.030.170.0985.82.51.50.190.010.050.030.170.0995.92.51.40.190.020.040.030.140.08

Composition of the Alloys in Percentage by Weight

[0055]The slabs have been homogenized at 480° C. and hot-rolled down to a thickness indicated in Table 2. The hot-rolling entry temperature was comprised between 38° and 410° C. The Examples 1, 2, 5, 8 and 9 have been transformed with a method that is not covered by the invention. As regards the plates 1, 2 and 5, a reference method has been applied wherein the reduction during the last pass has been at least 21% and for which the intermediate heat treatment has been performed in two succe...

Claims

1. A method for manufacturing a plate made of an aluminum alloy with a final thickness comprised between 6 and 25 mm, said method comprising successively,a) casting a rolling slab comprising an aluminum alloy with the composition, in weight %, Zn: 4.5-7.0; Mg: 1.2-3.5; Cu: 1.0-3.0; at least one element selected from among Cr: 0.04-0.35, Zr: 0.04-0.15 and Mn 0.04-0.5; Ti<0.25; Fe<0.6; Si<0.5; other elements <0.05 each and <0.15 in total, the remainder being aluminum,b) homogenizing said rolling slab,c) hot-rolling said rolling slab to obtain a plate with a thickness at least equal to 8 mm, the reduction rate upon the last hot-rolling pass being at most 20%,d) carrying out an intermediate heat treatment lasting at least 1 hour at a temperature between 100° C. and 350° C.,e) cold-rolling the heat treated plate with a reduction rate of 10% to 33%,f) carrying out a solution heat treatment of the cold-rolled plate and quenching it,g) stress relieving said solution heat treated and quenched plate by controlled stretching with a permanent elongation of 1 to 5%,h) carrying out an aging of the solution heat treated, quenched and optionally stress relieved plate,i) optionally, machining said aged plate to obtain a plate with a final thickness at least equal to 6 mm.

2. The method according to claim 1, wherein the homogenization temperature is comprised between 450° C. and 500° C.

3. The method according to claim 1, wherein the hot-rolling exit temperature is at most 355° C.

4. The method according to claim 1, wherein the heat treatment of d is carried out after hot-rolling is carried out at a temperature comprised between 130° C. and 320° C., and optionally at a temperature comprised between 200° C. and 300° C.

5. The method according to claim 1, wherein reduction rate by cold-rolling is 20% to 30%.

6. The method according to claim 1, wherein rolling speed during the last hot-rolling pass is at most 1,000 mm / s, optionally at most 900 mm / s and preferaMy optionally at most 800 mm / s.

7. A plate with a thickness comprised between 6 and 25 mm with a composition comprising, in weight %, Zn: 4.5-7.0; Mg: 1.2-3.5; Cu: 1.0-3.0; at least one element selected from among Cr: 0.04-0.35, Zr: 0.04-0.15 and Mn 0.04-0.5; Ti<0.25; Fe<0.6; Si<0.5; other elements <0.05 each and <0.15 in total, the remainder being aluminum, obtainable by the method according to claim 1.

8. The plate according to claim 7 having a tensile yield strength Rp0.2LT of at least 450 MPa, optionally at least 460 MPa and optionally at least 480 MPa, and / or an ultimate tensile strength RmLT of at least 500 MPa, optionally at least 520 MPa and optionally at least 540 MPa and / or an elongation at break A % of at least 6%, optionally at least 8% and optionally at least 10%.

9. The plate according to claim 7, wherein a product of the maximum deflection deviation in the L and LT directions multiplied by the final thickness is at most 3 and optionally at most 2, considered deflection deviations, in absolute value, to obtain a maximum value being, on one hand, a deflection deviation between deflection measured for a bar with the dimension 400 mm×30 mm×thickness at the exit of cold-rolling and the deflection measured for said bar after machining M of thickness thereof and, on another hand, a deflection deviation between deflection measured for a previous bar and a deflection measured for said previous bar after an additional machining of M of a thickness thereof, all deflection measurements being performed with the bar placed on two supports distant apart by 390 mm and the deflections being expressed in mm, all measurements being performed before final optional machining.

10. The plate according to claim 7, wherein the ratio of the sum of the planar compression texture volumetric fraction to the sum of the shear texture volumetric fraction is comprised between 0.5 and 1.5 and optionally between 0.6 and 1.3 between the mid-thickness and the surface after machining if machining has been carried out or 1.5 mm under the surface if no machining has been carried out.

11. A product comprising a plate according to claim 7 as a precision plate, optionally to make one or more machine bases, reference plates, transport tables, assembly jigs, robot arms or parts with a complex shape with material removal by machining.

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