Heat exchanger based on an aluminium alloy

Abstract

The present invention relates to an assembly having two sheets joined together, preferably by laser welding, comprising, preferably consisting of: a stamped part (12) formed from an aluminium alloy having the following composition: Si: from 2.50 to 6.50 wt%; Fe: up to 0.50 wt% and at least 0.05 wt%; Cu: up to 0.20 wt%; Mn: up to 0.40 wt%; Mg: from 0.05 to 0.50 wt%; Cr: from 0.05 to 0.35 wt%; Ti: from 0.02 to 0.30 wt%; Sr: up to 500 ppm; inevitable impurities < 0.05 wt% each and < 0.15 wt% in total, the remainder being aluminium; and a flat part (11) formed from an aluminium alloy; the two parts being joined together so as to form a channel (13) by virtue of the deformation of the stamped part (12).

Description

[0001] DESCRIPTION

[0002] Title: Heat exchanger based on an aluminum alloy

[0003] Technical field

[0004] The invention relates to thin strips or sheets (generally with a thickness of 0.5 to 3 mm) made of aluminium alloy. These strips or sheets are intended in particular for the manufacture of elements, such as heat exchanger plates assembled in pairs or more, in particular for the automobile industry, such as battery coolers for electric vehicles.

[0005] Prior art

[0006] With the development of electric vehicles, the battery cooler market is booming. The current purpose of this part is to control the operating temperature of batteries, generally in a range of 20 to 100°C, preferably 30 to 80°C. The parts can be large (1 to 2 meters).

[0007] An example of a current design of an electric vehicle battery cooler is shown in Figure 1. It is composed of two parts with a core layer of 3xxx series aluminum alloy 15: a flat part 11 and a stamped part 12, assembled so as to create a channel 13. In the present description, the term "flat part" designates a part that is not stamped before assembly. On the other hand, the term "stamped part" designates a part that is stamped before assembly, so as to create a channel after assembly with a flat part. In use, the channel 13 is used for the circulation of the cooling fluid in the electric vehicle battery cooler. In addition to the core layer of 3xxx series aluminum alloy 15, a sacrificial layer 16, for example of 7xxx or lxxx series aluminum alloy, may be added to ensure SWAAT corrosion resistance on the external face of each of the two parts 11 and 12.The stamped part 12 also includes a 4xxx series aluminum alloy brazing layer 17, on the other side of the 3xxx series aluminum alloy core layer 15 from the sacrificial layer 16, to ensure brazing of the two parts 11 and 12 together. The batteries 14 are in contact with the flat part 11, but not with the stamped part 12.

[0008] The properties required for aluminum alloy strips or sheets used for the manufacture of heat exchangers include sufficient formability for easy shaping of the plates before assembly, good assembly capability, high mechanical strength after assembly, so as to use thicknesses as small as possible and provide part of the strength of the complete structure of the battery box, good resistance to fatigue stress in service, and good corrosion resistance after assembly. Of course, it is important that the aluminum alloy chosen is easy to cast and roll, and that the manufacturing cost of the strips or sheets is compatible with the requirements of the automotive industry.

[0009] In order to promote the reduction of plate thickness for heat exchangers (such as battery coolers for electric vehicles, which can potentially also serve as structural parts), it is particularly interesting to increase the mechanical properties of the material after assembly, without reducing corrosion resistance.

[0010] Another current market demand is to improve the recycling possibilities of aluminum alloy strips or sheets used for the manufacture of heat exchangers, especially battery coolers for electric vehicles.

[0011] Solutions have been proposed in this regard. Examples include the following patents and patent applications:

[0012] - EP3790100 (Novelis): discloses a 3xxx alloy comprising from 0.5 to 1.15% Mn and up to 0.15% Mg;

[0013] - EP3741876 (Novelis): discloses a 3xxx alloy comprising from 0.5 to 1.15% Mn and up to 0.06% Mg, which is plated with a 4xxx alloy;

[0014] - WO2013 / 06853 (Novelis): discloses an Al-Si-Cu alloy for welding, but not in the field of battery coolers;

[0015] - WO2018 / 115638 (Constellium Neuf-Brisach): discloses an aluminum alloy comprising 2.5 to 14% Si, 0.05 to 0.8% Fe, 0.25 to 1.0% Cu, 0.05 to 0.8% Mg, up to 0.70% Mn, up to 0.35% Cr, 0.02 to 0.30% Ti, up to 500 ppm Sr, up to 200 ppm Na and up to 0.15% Sb, for welding in the field of automotive sheet metal;

[0016] - W02017 / 001790 (Constellium Neuf-Brisach): discloses an aluminum alloy comprising 2.5 to 14% Si, 0.05 to 0.8% Fe, up to 0.20% Cu, 0.05 to 0.80% Mg, up to 0.70% Mn, up to 0.35% Cr, 0.02 to 0.30% Ti, up to 500 ppm Sr, up to 200 ppm Na and up to 0.15% Sb, for welding in the field of automotive sheet metal.

[0017] But the proposed solutions do not necessarily allow for the right compromise between good mechanical resistance after assembly, good corrosion resistance and better recyclability.

[0018] Faced with growing market demand, there remains a need for a new core alloy with improved mechanical strength compared to existing alloys, without degradation of corrosion resistance and allowing for improved recyclability. Such a core alloy could help meet the ever-present demand for product thickness reduction and the demand to develop solutions with high mechanical properties for battery coolers in order to improve their contribution to the overall strength of the structure protecting the batteries (which includes the battery cooler, but also the parts encapsulating the batteries, whether integrated into the vehicle body or not).

[0019] Statement of the invention

[0020] The applicant has determined a composition range which, surprisingly, makes it possible to improve mechanical resistance and recyclability without degrading corrosion resistance.

[0021] The solution according to the present invention is notably based on the use of:

[0022] - A monolithic material, which can be recycled more easily than a multi-layer material, because there is no need to manage the differences in composition of the alloys used for the different layers; and

[0023] - Laser welding, which does not affect the mechanical properties of the material like brazing could.

[0024] The combination of these two elements can allow the use of stronger materials and a lighter final structure, while improving recyclability and maintaining corrosion resistance. Thus, the solution according to the present invention meets market demands: mechanical performance, corrosion resistance, recyclability / environmental performance and cost-effectiveness.

[0025] Corrosion resistance is typically measured by a 40-day SWAAT test according to ASTM G85 (August 2003).

[0026] The environmental performance of an aluminum alloy product can be measured, in particular, by its carbon footprint at the time of delivery. This carbon footprint can be improved, i.e., reduced, by increasing the level of recycled content included in the aluminum alloy. The more tolerant an alloy is to impurities, the more suitable it is for recycling.

[0027] Profitability can be measured in particular by the cost of the raw material used for the manufacture of the strip or sheet and by the cost of processing the strip or sheet to obtain a heat exchanger.

[0028] In the case of a laser-welded heat exchanger (without filler wire), the possibility of using a monolithic material improves the cost compared to a multi-layer material (core associated with one or more plated covers), which is more expensive to prepare. But to further reduce the cost, it is possible to reduce the size of the two parts, flat and stamped. To reduce this size while maintaining mechanical performance, the mechanical strength of the plates in service seems to be the key parameter, and in particular the yield strength (YS or RpO.2) and the maximum tensile strength (UTS or Rm). The multi-layer solutions currently developed aim for a YS preferably greater than or equal to 160 MPa, preferably greater than or equal to 200 MPa. This target is maintained for the present invention.

[0029] On the other hand, since significant lengths must be welded to prepare large cooling plates, the cost of laser processing is directly proportional to the welding speed: the faster the welding, the shorter the welding cycle (tak time) and the lower the processing cost. But it is also important to ensure good weld quality. This quality is generally determined by the depth of the weld in the second sheet, knowing that the first sheet is completely penetrated, since this is a so-called overlap weld (see Figure 2). A typical objective is a weld penetration depth of 20 to 80% of the thickness of the second sheet.

[0030] In summary, the present invention provides a material:

[0031] - satisfactory in terms of corrosion (maximum 30% pitting depth after 40 days of SWAAT testing, relative to the sheet thickness);

[0032] - as strong as possible (YS preferably greater than or equal to 160 MPa, preferably greater than or equal to 200 MPa);

[0033] - quick to weld (preferably at a welding speed of the order of 10 to 30 m / min) by laser overlap welding, with an acceptable weld quality (according to ISO 13919-2: weld penetration depth of 20% to 80%, undercut height, overfill height, welded interface width (= bead), presence of cracks and / or blowholes, etc. - see Figure 3); The present invention can make it possible to obtain class A or B quality welds according to ISO 13919-2;

[0034] - Ideally monolithic for cost and environmental performance / recyclability reasons.

[0035] The invention thus relates to a set of two sheets assembled, preferably by laser welding, comprising, preferably consisting of:

[0036] - a stamped part 12, formed from an aluminum alloy having the following composition, in mass percentages: Si: from 2.50 to 6.50%; preferably from 3.0 to 6.0%, preferably from 3.50 to 5.50%, preferably from 4.0 to 5.0%, from 4.25 to 4.75%;

[0037] Fe: up to 0.50%, preferably up to 0.40%, preferably up to 0.30%, preferably up to 0.25%; and at least 0.05%, preferably at least 0.10%, preferably at least 0.15%;

[0038] Cu: up to 0.20%, preferably up to 0.17%, preferably up to 0.15%, preferably up to 0.12%; and preferably at least 10 ppm, preferably at least 20 ppm, preferably at least 40 ppm, preferably at least 60 ppm;

[0039] Mn: up to 0.40%, preferably up to 0.30%, preferably up to 0.20%; and preferably at least 0.05%, preferably at least 0.08%, preferably at least 0.10%;

[0040] Mg: from 0.05 to 0.50%, preferably from 0.08 to 0.45%, preferably from 0.10 to 0.40%, preferably from 0.10 to 0.35%, -

[0041] Cr: from 0.05 to 0.35%, preferably from 0.06 to 0.30%, preferably from 0.08 to 0.25%, preferably from 0.10 to 0.20%, preferably from 0.10 to 0.15%, -

[0042] Ti: from 0.02 to 0.30%, preferably from 0.04 to 0.25%, preferably from 0.05 to 0.25%, preferably from 0.07 to 0.20%, preferably from 0.10 to 0.20%, -

[0043] Sr: up to 500 ppm, preferably up to 450 ppm, preferably up to 400 ppm, preferably up to 350 ppm, and preferably at least 50 ppm, preferably at least 100 ppm, preferably at least 150 ppm, preferably at least 200 ppm, preferably at least 250 ppm; unavoidable impurities < 0.05% each and < 0.15% in total, remainder aluminum; and

[0044] - a flat part 11, formed from an aluminum alloy, preferably the same aluminum alloy as the stamped part 12 or a 6xxx alloy or a 5xxx alloy; the two parts being assembled so as to form a channel 13 thanks to the deformation of the stamped part 12.

[0045] The invention according to the first object uses an aluminum alloy making it possible to maintain good resistance to corrosion while simultaneously improving:

[0046] - the environmental performance and recyclability of the material, as it is more tolerant to waste, such as scrap, than usual 6xxx alloys or plated materials;

[0047] - the mechanical strength of the material, preferably using specific metallurgical states; the laser welding speed. The invention also relates to a method for manufacturing a strip, intended to produce a sheet used according to the present invention, comprising the successive steps of: a. Casting the aluminum alloy according to claim 1 into a plate, preferably by vertical semi-continuous casting; b. Homogenizing the plate, at a homogenization temperature preferably comprised between 490 and 550°C, for a holding time preferably greater than or equal to 2 hours; c. Hot rolling to obtain a strip, the hot rolling start temperature preferably being between 450 and 550°C and the hot rolling end temperature preferably being between 250 and 380°C; d.Cold rolling of the strip, with optional intermediate annealing, the reduction in thickness of the strip during cold rolling preferably being 50 to 75%; e. Solution treatment followed by quenching, preferably in air; f. Optionally pre-tempering, at a pre-tempering temperature preferably of 50 to 120°C, for a period preferably of 2 to 16 hours, preferably obtained by coiling and then cooling to room temperature; g. Additional tempering in a batch furnace, with a temperature maintenance period of 20 minutes to 24 hours and a metal temperature of 100 to 210°C.

[0048] The invention also relates to a method of manufacturing a sheet metal, used as a flat part 11 according to the present invention, comprising the successive steps of:

[0049] - manufacturing a strip according to the method of the present invention;

[0050] - cutting into the desired dimensions.

[0051] The invention also relates to a method for manufacturing a sheet metal, used as a stamped part 12 according to the present invention, comprising the successive steps of:

[0052] - manufacturing a strip according to the method of the present invention;

[0053] - cutting into the desired dimensions;

[0054] - stamping so as to create a channel 13 after assembly between a flat part 11 and a stamped part 12; the cutting and stamping can be carried out in any order.

[0055] The invention also relates to a method for manufacturing a set of two sheets according to the present invention, comprising the steps of:

[0056] - providing two sheets, one of the sheets forming a flat part 11 and the other sheet forming a stamped part 12, manufactured respectively according to the corresponding methods of the present invention; - assembling the two flat parts 11 and stamped 12, preferably by laser welding, preferably remotely without filler wire, preferably by overlapping, so as to form a channel 13 thanks to the deformation of the stamped part 12.

[0057] The invention also relates to a heat exchanger, preferably a battery cooler for an electric vehicle, made at least in part from a set of two sheets according to the present invention.

[0058] The invention also relates to the use of a set of two sheets according to the present invention or obtained according to the method of the present invention, for the manufacture of a heat exchanger, preferably a battery cooler for an electric vehicle.

[0059] Figures

[0060] [Figure 1] is a cross-sectional diagram depicting a current design of an electric vehicle battery cooler.

[0061] [Figure 2] is a cross-sectional diagram of a laser lap welded assembly.

[0062] [Figure 3] is a cross-sectional diagram of a lap weld with the quality criteria according to EN ISO 13919-2 (January 2021).

[0063] Detailed description of the invention

[0064] In this description and the claims, unless otherwise indicated:

[0065] - All aluminum alloys are designated according to the rules and designations defined by the “Aluminum Association” in the “Registration Record Series” which it publishes regularly.

[0066] - The compositions are expressed in mass percentages. The expression 1.4 Cu means that the copper content expressed in mass percentages is 1.4%.

[0067] - Alloy groups, also called series, are defined according to European standard EN 573-1 (February 2005).

[0068] - Metallurgical states are defined according to European standard EN-515 (April 2017).

[0069] - 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%, are determined by a tensile test according to standard NF EN ISO 6892-1, the sampling and the direction of the test being defined by standard EN 485-1 (December 2009), the direction or direction L corresponds to the lengthwise direction in relation to the main rolling direction and the direction or direction TL corresponds to the cross-long direction.

[0070] The definitions of EN 12258-1 (July 2012) apply. Aluminium alloy

[0071] The composition limits of the aluminum alloy of the stamped part used according to the present invention are expressed in mass percentages and can be justified as follows.

[0072] Silicon:

[0073] A minimum Si content of 2.50% can improve weldability and mechanical properties, in particular by the formation of hardening precipitates containing magnesium and silicon during post-assembly heat treatments. The silicon content is therefore greater than or equal to 2.50%, preferably greater than or equal to 2.60%, or greater than or equal to 2.75%, or greater than or equal to 2.90%, or greater than or equal to 3.00%, or greater than or equal to 3.10%, or greater than or equal to 3.25%, or greater than or equal to 3.40%, or greater than or equal to 3.50%, or greater than or equal to 3.60%, or greater than or equal to 3.75%, or greater than or equal to 3.90%, or greater than or equal to 4.00%, or greater than or equal to 4.10%, or greater than or equal to 4.25%.

[0074] Too high a Si content can reduce formability. It is then desirable to limit the Si content to a content less than or equal to 6.50%, preferably less than or equal to 6.40%, or less than or equal to 6.25%, or less than or equal to 6.10%, or less than or equal to 6.00%, or less than or equal to 5.90%, or less than or equal to 5.75%, or less than or equal to 5.60%, or less than or equal to 5.50%, or less than or equal to 5.40%, or less than or equal to 5.25%, or less than or equal to 5.10%, or less than or equal to 5.00%, or less than or equal to 4.90%, or less than or equal to 4.75%.

[0075] Iron :

[0076] A minimum Fe content of 0.05% can unexpectedly improve weldability, while for a content above 0.50% formability can be significantly degraded.

[0077] A maximum Fe content is thus 0.50%, or preferably 0.49%, or 0.48%, or 0.47% or 0.46%, or 0.45%, or 0.44%, or 0.43%, or 0.42%, or 0.41%, or 0.40%, or 0.39%, or 0.38%, or 0.37% or 0.36%, or 0.35%, or 0.34%, or 0.33%, or 0.32%, or 0.31%, or 0.30%, or 0.29%, or 0.28%, or 0.27%, or 0.26% or 0.25%. However, it is not necessary to go down to very low contents, for example below 0.05%, which would lead to high cost prices. Therefore, the minimum Fe content is 0.05%, or preferably 0.06%, or 0.07%, or 0.08%, or 0.09%, or 0.10%, or 0.11%, or 0.12%, or 0.13%, or 0.14%, or 0.15%. Copper:

[0078] Cu is a hardening element that contributes to mechanical strength. However, beyond a certain content, the risk of cracking during casting is higher. Coarse intermetallic compounds can also form during casting, which impair the homogeneity of the metal and can constitute sites for corrosion initiation. Surprisingly, the inventors found that adding up to 0.20% by mass of Cu can improve mechanical characteristics, while not significantly degrading weldability or corrosion resistance. The Cu content is therefore less than or equal to 0.20%, or less than or equal to 0.19%, or less than or equal to 0.18%, or less than or equal to 0.17%, or less than or equal to 0.16%, or less than or equal to 0.15%, or less than or equal to 0.14%, or less than or equal to 0.13%, or less than or equal to 0.12%.Preferably, the Cu content is greater than or equal to 10 ppm, or greater than or equal to 15 ppm, or greater than or equal to 20 ppm, or greater than or equal to 25 ppm, or greater than or equal to 30 ppm, or greater than or equal to 35 ppm, or greater than or equal to 40 ppm, or greater than or equal to 45 ppm, or greater than or equal to 50 ppm, or greater than or equal to 55 ppm, or greater than or equal to 60 ppm.

[0079] Manganese:

[0080] Manganese addition beyond 0.05% can increase mechanical characteristics by solid solution effect, but beyond 0.50% it can decrease formability.

[0081] Also, according to the present invention, the Mn content is preferably greater than or equal to 0.05%, or greater than or equal to 0.06%, or greater than or equal to 0.07%, or greater than or equal to 0.08%, or greater than or equal to 0.09%, or greater than or equal to 0.10%.To avoid forming a significant number of coarse phases during casting which may reduce formability, it is recommended according to the present invention to limit the Mn to a content less than or equal to 0.40%, or less than or equal to 0.39%, or less than or equal to 0.38%, or less than or equal to 0.37%, or less than or equal to 0.36%, or less than or equal to 0.35%, or less than or equal to 0.34%, or less than or equal to 0.33%, or less than or equal to 0.32%, or less than or equal to 0.31%, or less than or equal to 0.30%, or less than or equal to 0.29%, or less than or equal to 0.28%, or less than or equal to 0.27%, or less than or equal to 0.26%, or less than or equal to 0.25%, or less than or equal to 0.24%, or less than or equal to 0.23%, or less than or equal to 0.22%, or less than or equal to 0.21%, or less than or equal to 0.20%.

[0082] Magnesium:

[0083] A minimum Mg content of 0.05% can allow the formation of Mg2Si precipitates in order to obtain sufficient mechanical characteristics. Its negative influence on welding imposes a limitation to a maximum content of 0.50%. Also, the minimum Mg content according to the present invention is greater than or equal to 0.05%, or greater than or equal to 0.06%, or greater than or equal to 0.07%, or greater than or equal to 0.08%, or greater than or equal to 0.09%, or greater than or equal to 0.10%.Furthermore, the maximum Mg content according to the present invention is less than or equal to 0.50% or less than or equal to 0.49%, or less than or equal to 0.48%, or less than or equal to 0.47%, or less than or equal to 0.46%, or less than or equal to 0.45%, or less than or equal to 0.44%, or less than or equal to 0.43%, or less than or equal to 0.42%, or less than or equal to 0.41%, or less than or equal to 0.40% or less than or equal to 0.39%, or less than or equal to 0.38%, or less than or equal to 0.37%, or less than or equal to 0.36%, or less than or equal to 0.35%.

[0084] Chrome:

[0085] The addition of Cr can improve weldability. In addition, an addition of 0.05% or more of Cr can have a hardening effect, but above 0.35%, chromium can form harmful intermetallic phases.

[0086] The Cr content according to the present invention is thus less than or equal to 0.35%, or less than or equal to 0.34%, or less than or equal to 0.33%, or less than or equal to 0.32%, or less than or equal to 0.31%, or less than or equal to 0.30%, or less than or equal to 0.29%, or less than or equal to 0.28%, or less than or equal to 0.27%, or less than or equal to 0.26%, or less than or equal to 0.25%, or less than or equal to 0.24%, or less than or equal to 0.23%, or less than or equal to 0.22%, or less than or equal to 0.21%, or less than or equal to 0.20%, or less than or equal to 0.19%, or less than or equal to 0.18%, or less than or equal to 0.17%, or less than or equal to 0.16%, or less than or equal to 0.15%.Furthermore, the minimum Cr content according to the present invention is greater than or equal to 0.05%, or greater than or equal to 0.06%, or greater than or equal to 0.07%, or greater than or equal to 0.08%, or greater than or equal to 0.09%, or greater than or equal to 0.10%.

[0087] Titanium:

[0088] It has been noted that Ti has the effect of refining the solidification structure and therefore reducing the sensitivity to cracking. A minimum Ti content of 0.02% is thus recommended according to the present invention. Furthermore, a maximum Ti content of 0.30% seems to prevent the formation of primary phases during (vertical) casting, which have a detrimental effect on the mechanical characteristics and formability.

[0089] The Ti content according to the present invention is thus less than or equal to 0.30%, or less than or equal to 0.29%, or less than or equal to 0.28%, or less than or equal to 0.27%, or less than or equal to 0.26%, or less than or equal to 0.25%, or less than or equal to 0.24%, or less than or equal to 0.23%, or less than or equal to 0.22%, or less than or equal to 0.21%, or less than or equal to 0.20%. Furthermore, the minimum Ti content according to the present invention is greater than or equal to 0.02%, or greater than or equal to 0.03%, or greater than or equal to 0.04%, or greater than or equal to 0.05%, or greater than or equal to 0.06%, or greater than or equal to 0.07%, or greater than or equal to 0.08%, or greater than or equal to 0.09%, or greater than or equal to 0.10%.

[0090] Strontium:

[0091] The addition of Sr is optional. At a content of less than 500 ppm, it can influence the shape of the Al-Si eutectic during solidification and promote the production of circular and homogeneously distributed Si particles after reheating and before hot rolling. Above this content, its effect on the gassing of the cast plate can become significant. The maximum strontium content is less than or equal to 500 ppm, or less than or equal to 490 ppm, or less than or equal to 480 ppm, or less than or equal to 470 ppm, or less than or equal to 460 ppm, or less than or equal to 450 ppm, or less than or equal to

[0092] 440 ppm, or less than or equal to 430 ppm, less than or equal to 420 ppm, or less than or equal to 410 ppm, or less than or equal to 400 ppm, or less than or equal to 390 ppm, or less than or equal to 380 ppm, or less than or equal to 370 ppm, or less than or equal to

[0093] 360 ppm, or less than or equal to 350 ppm. Furthermore, the minimum strontium content is preferably greater than or equal to 50 ppm, or greater than or equal to 60 ppm, or greater than or equal to 70 ppm, or greater than or equal to 80 ppm, or greater than or equal to 90 ppm, or greater than or equal to 100 ppm, or greater than or equal to 110 ppm, or greater than or equal to 120 ppm, or greater than or equal to 130 ppm, or greater than or equal to 140 ppm, or greater than or equal to 150 ppm, or greater than or equal to 160 ppm, or greater than or equal to 170 ppm, or greater than or equal to 180 ppm, or greater than or equal to 190 ppm, or greater than or equal to 200 ppm, or greater than or equal to 210 ppm, or greater than or equal to 220 ppm, or greater than or equal to 230 ppm, or greater than or equal to 240 ppm, or greater than or equal to 250 ppm.

[0094] The use of other so-called "modifying elements", such as sodium (Na) at contents up to 200 ppm or antimony (Sb) at contents up to 0.15%, is also possible as an option. A preferred Na content is 20 to 200 ppm. A preferred Sb content is 0.04 to 0.15%. In an advantageous embodiment, the addition of Sr alone is chosen.

[0095] The other elements are not intentionally added. They are unavoidable impurities with a content of less than 0.05% each and less than 0.15% in total. The remainder is aluminum.

[0096] It should be noted that the aluminum alloy of the flat 11 and stamped 12 parts may be the same alloy or two different alloys. According to one variant, it is the same alloy. According to another variant, it is two different alloys, the alloy of the flat part 11 preferably being an alloy of type 5xxx or 6xxx, preferably of type AA5083, or AA 5754, or AA6005, or AA6016.

[0097] Alternatively, the 5xxx type alloy used for the stamped part is an AA5083 type alloy, which preferably has the following composition, in mass percentages: up to 0.40% Si; up to 0.40% Fe; up to 0.10% Cu; 0.40 to 1.0% Mn; 4.0 to 4.9% Mg; 0.05 to 0.25% Cr; up to 0.25% Zn; up to 0.15% Ti; unavoidable impurities with a content of less than 0.05% each and less than 0.15% in total; the remainder being aluminum.

[0098] According to a variant, the 5xxx type alloy used for the stamped part is an AA5754 type alloy, which preferably has the following composition, in mass percentages: up to 0.40% Si; up to 0.40% Fe; up to 0.10% Cu; up to 0.50% Mn; 2.6 to 3.6% Mg; up to 0.30% Cr; up to 0.20% Zn; up to 0.15% Ti; 0.10 to 0.6% Mn+Cr; unavoidable impurities whose content is less than 0.05% each and less than 0.15% in total; the remainder being aluminum.

[0099] According to a variant, the 6xxx type alloy used for the stamped part is an AA6005 type alloy, which preferably has the following composition, in mass percentages: from 0.6 to 0.9% Si; up to 0.35% Fe; up to 0.10% Cu; up to 0.10% Mn; from 0.40 to 0.6% Mg; up to 0.10% Cr; up to 0.10% Zn; up to 0.10% Ti; unavoidable impurities whose content is less than 0.05% each and less than 0.15% in total; the remainder being aluminum.

[0100] According to a variant, the 6xxx type alloy used for the stamped part is an AA6016 type alloy, which preferably has the following composition, in mass percentages: from 1.0 to 1.5% Si; up to 0.50% Fe; up to 0.20% Cu; up to 0.20% Mn; from 0.25 to 0.6% Mg; up to 0.10% Cr; up to 0.20% Zn; up to 0.15% Ti; unavoidable impurities whose content is less than 0.05% each and less than 0.15% in total; the remainder being aluminum.

[0101] Strip or sheet:

[0102] As known to those skilled in the art, the term "plate" corresponds to the aluminum alloy from casting until the start of rolling. The term "strip" corresponds to the aluminum alloy from the start of rolling until the end of coiling. The term "sheet" corresponds to the aluminum alloy after cutting the strip. According to a first variant where the strip or sheet according to the present invention is intended for the manufacture of a flat part 11, the minimum total thickness of the strip or sheet is 0.60 mm, or 0.65 mm, or 0.70 mm, or 0.75 mm, or 0.80 mm. According to this first variant, the maximum total thickness of the strip or sheet is preferably 3.50 mm, or 3.40 mm, or 3.30 mm, or 3.20 mm, or 3.10 mm, or 3.00 mm, or 2.90 mm, or 2.80 mm, or 2.70 mm.

[0103] According to a second variant where the strip or sheet according to the present invention is intended for the manufacture of a stamped part 12, the minimum total thickness of the strip or sheet is 0.50 mm, or 0.55 mm, or 0.60 mm, or 0.65 mm, or 0.70 mm. According to this second variant, the maximum total thickness of the strip or sheet is preferably 1.50 mm, or 1.45 mm, or 1.40 mm, or 1.35 mm, or 1.30 mm.

[0104] Set of two sheets:

[0105] The sheets according to the present invention can be combined with each other, after possible shaping, to form a heat exchanger with channels.

[0106] According to the present invention, the set of two sheets comprises, preferably consists of:

[0107] - a stamped part 12, formed from an aluminum alloy having the following composition, in mass percentages:

[0108] If: from 2.50 to 6.50%; preferably from 3.0 to 6.0%, preferably from 3.50 to 5.50%, preferably from 4.0 to 5.0%, from 4.25 to 4.75%;

[0109] Fe: up to 0.50%, preferably up to 0.40%, preferably up to 0.30%, preferably up to 0.25%; and at least 0.05%, preferably at least 0.10%, preferably at least 0.15%;

[0110] Cu: up to 0.20%, preferably up to 0.17%, preferably up to 0.15%, preferably up to 0.12%; and preferably at least 10 ppm, preferably at least 20 ppm, preferably at least 40 ppm, preferably at least 60 ppm;

[0111] Mn: up to 0.40%, preferably up to 0.30%, preferably up to 0.20%; and preferably at least 0.05%, preferably at least 0.08%, preferably at least 0.10%;

[0112] Mg: from 0.05 to 0.50%, preferably from 0.08 to 0.45%, preferably from 0.10 to 0.40%, preferably from 0.10 to 0.35%, -

[0113] Cr: from 0.05 to 0.35%, preferably from 0.06 to 0.30%, preferably from 0.08 to 0.25%, preferably from 0.10 to 0.20%, preferably from 0.10 to 0.15%, -

[0114] Ti: from 0.02 to 0.30%, preferably from 0.04 to 0.25%, preferably from 0.05 to 0.25%, preferably from 0.07 to 0.20%, preferably from 0.10 to 0.20%;

[0115] Sr: up to 500 ppm, preferably up to 450 ppm, preferably up to 400 ppm, preferably up to 350 ppm, and preferably at least 50 ppm, preferably at least 100 ppm, preferably at least 150 ppm, preferably at least 200 ppm, preferably at least 250 ppm; unavoidable impurities < 0.05% each and < 0.15% in total, remainder aluminum; and

[0116] - a flat part 11, formed from an aluminum alloy, preferably the same aluminum alloy as the stamped part 12 or a 6xxx alloy or a 5xxx alloy; the two parts being intended to be assembled by welding, preferably remotely without filler wire, preferably by laser welding, preferably of the “Remote Laser Welding” type, so as to form a channel 13 thanks to the deformation of the stamped part 12.

[0117] Remote Laser Welding is a type of welding that is carried out remotely and it is not the laser effector (or welding head) itself that moves to weld at different locations, but a mirror that moves to reflect the laser beam at said different locations. The ISO 15609-4 (May 2009) and ISO 4063 (August 2009) standards describe the operating mode of this technique. The ISO 13919-2 (January 2021) standard gives recommendations for the quality of the welds obtained.

[0118] Preferably, the weld between the flat part 11 and the stamped part 12 is continuous.

[0119] Method of manufacturing a strip

[0120] The invention also relates to a method for manufacturing a strip, intended to produce a sheet according to the present invention, comprising the successive steps of: a. Casting the aluminum alloy according to the present invention into a plate, preferably by vertical semi-continuous casting; b. Homogenization of the plate, at a homogenization temperature preferably comprised between 490 and 550°C, for a holding time preferably greater than or equal to 2 hours; c. Hot rolling, the hot rolling start temperature preferably being between 450 and 550°C and the hot rolling end temperature preferably being between 250 and 380°C; d. Cold rolling of the strip, with optionally an intermediate annealing, the reduction in thickness of the strip during cold rolling preferably being between 50 and 75%; e. Solution treatment then quenching, preferably in air; f.Optionally pre-tempered, at a pre-tempering temperature preferably of 50 to 120°C, for a period preferably of 2 to 16 hours, preferably obtained by coiling then cooling to room temperature; g. Additional tempering in a batch furnace, with a temperature maintenance for a period of 20 minutes to 24 hours and a metal temperature of 100 to 210°C.

[0121] The process for manufacturing monolithic strips or sheets according to the present invention typically comprises casting, reheating / homogenizing, hot rolling, cold rolling, solution processing and quenching.

[0122] The method for manufacturing the strips or sheets according to the invention comprises casting a plate, preferably by vertical semi-continuous casting, followed by scalping. In one embodiment, the casting may be continuous.

[0123] The preferred dimensions of the plates according to the invention are 200 to 600 mm, preferably 450 to 510 mm, in thickness, 1000 to 3000 mm in width and 2000 to 8000 mm in length.

[0124] Advantageously, the manufactured sheet metal is monolithic. This is less expensive than a plated sheet metal and more suitable for recycling.

[0125] The plate is homogenized, typically at a homogenization temperature above the solvus temperature of the alloy, while avoiding local melting or burning, preferably for a minimum of 2 hours, preferably 3 hours, and preferably for a maximum of 7 hours, preferably 6 hours. The homogenization temperature is preferably a maximum of 550°C, preferably 540°C, preferably 530°C, and preferably a minimum of 490°C, preferably 500°C. Too high or too low a temperature can degrade the mechanical properties of the sheet.

[0126] The plate is then transferred to the hot rolling mill. Optionally, it is directly transferred from homogenization to hot rolling, the temperature being able to decrease by 5 to 40°C naturally during this transfer. Optionally, the plate is cooled from the homogenization temperature to the hot rolling start temperature by forced cooling. This forced cooling is preferably carried out with a direct cooling rate of at least 150°C per hour. Advantageously, the direct cooling rate is at most 500°C / h. The cooling can typically be carried out by a machine such as that described by application WO2016012691. Preferably, this cooling is done in two stages, one of spraying and the other of uniformization. Optionally, this cooling can be carried out in two passes in the machine such as that described by application WO2016012691.

[0127] The homogenized plate is then hot rolled, preferably to a strip thickness of 2 to 7.3 mm. The hot rolling start temperature is preferably 450 to 550°C. Preferably, the hot rolling start temperature is at least 460°C, or at least 470°C, or at least 480°C, or at least 490°C. Preferably, the hot rolling start temperature is at most 545°C, or at most 540°C, or at most 535°C or at most 530°C, or at most 525°C.

[0128] The temperature change between the start and the end of hot rolling results from cooling by the usual heat exchange of the strip with the air at the ambient temperature of the factory, with the equipment of the hot rolling mill such as, for example, but not limited to, the cylinders or the conveyor rollers as well as with the usual lubrication or cooling fluids and from the heating linked to the deformation energy. Preferably, the end temperature of hot rolling is from 250°C to 380°C. Preferably, the end temperature of hot rolling is at least 260°C, or at least 270°C, or at least 280°C, or at least 290°C. Preferably, the hot rolling end temperature is at most 370°C, or at most 360°C, or at most 350°C, or at most 340°C, or at most 330°C, or at most 320°C.

[0129] The hot-rolled strip is then cold-rolled, preferably to a strip thickness of 0.5 to 3.5 mm. Preferably, the reduction in strip thickness during cold rolling is 50 to 75%. Intermediate annealing may also take place between two cold rolling steps. Intermediate annealing may optionally take place, in a static furnace or in a continuous furnace, preferably at a temperature of 300 to 350°C.

[0130] The strip is then solution-treated, typically at a solution temperature above the solvus temperature of the alloy, while avoiding local melting or burning, and then quenched, preferably in a continuous furnace. Too cold a solution treatment and / or too short a solution treatment can degrade the mechanical properties of the strip or sheet by insufficient solution treatment. Too hot a solution treatment can cause burns degrading the mechanical properties. Too long a solution treatment can degrade productivity. Preferably, solution treatment lasts from 15 to 300 seconds. The solution treatment temperature is preferably at least 530°C and at most 560°C.

[0131] Then, the strip is quenched, typically at a rate of more than 30°C / s and better still at least 100°C / s, with water or air or a successive combination of water and / or air. Preferably, the strip is quenched to a temperature of 60 to 100°C. An insufficient cooling rate can degrade the mechanical properties of the strip or sheet, because the solution treatment is then incomplete.

[0132] The strip may optionally be reheated to perform pre-tempering at a pre-tempering temperature of 50 to 120°C, preferably 50 to 110°C, or 100°C, or 90°C or 80°C, for a period preferably of 2 to 16 hours. Reheating may be useful when the strip undergoes, between quenching and pre-tempering, a surface treatment whose temperature is lower than that of the pre-tempering. The surface treatment may for example be pickling followed by the application of a conversion layer. Preferably, the pre-tempering is carried out by coiling, then cooling to room temperature, preferably for at least 40 hours.

[0133] The pre-tempered strip is in the T4 state and can then optionally mature at room temperature for 72 hours to 6 months. This step is a constraint linked to storage before shaping. The strip according to the invention can be shaped despite maturation. Maturation occurs naturally between the end of winding and the moment when the coil is actually used.

[0134] The T4 metallurgical state thus obtained has the advantage of good formability.

[0135] The strip can then be subjected to additional tempering in a batch furnace, with a temperature holding time of 20 minutes to 24 hours and a metal temperature of 100 to 210°C. Additional tempering can allow different metallurgical states to be obtained, such as T61, T6 or T7. The T61 metallurgical state has the particular advantage of being harder than the T4 metallurgical state, while conceding a slightly less good formability. The T6 metallurgical state has the particular advantage of being the hardest metallurgical state among the T6x and T7x metallurgical states. The T7 metallurgical state has the particular advantage of a better resistance to SWAAT corrosion and intergranular corrosion.

[0136] Manufacturing process of a flat part:

[0137] To obtain a flat part 11 according to the present invention, it is sufficient to cut the strip previously obtained according to the present invention, in the desired dimensions, which can preferably be between 100 mm x 200 mm and 2000 mm x 3500 mm. Method of manufacturing a stamped part:

[0138] To obtain a stamped part 12, it is necessary to follow the method of manufacturing a strip as described previously according to the present invention, and it is necessary to cut said strip into the desired dimensions and stamp it in order to form a channel 13 after assembly with a flat part 11, said channel 13 being adapted to the circulation of a cooling fluid. The aforementioned cutting and stamping steps can be in one order or the other, that is to say that the strip can first be cut to obtain a sheet, then the sheet is then stamped, or the strip can first be stamped and then cut to obtain a stamped sheet.

[0139] The dimensions of the stamped part 12 are preferably between 100 mm x 200 mm and 2000 mm x 3500 mm.

[0140] Manufacturing process for a set of two sheets:

[0141] The method of manufacturing a set of two sheets according to the present invention comprises the steps of:

[0142] - Provision of two sheets, one of the sheets forming a flat part 11 and the other sheet forming a stamped part 12, manufactured respectively according to the corresponding methods of the present invention;

[0143] - Assembly of the two flat parts 11 and stamped part 12, preferably by laser welding, preferably remotely without filler wire, preferably by overlapping, so as to form a channel 13 thanks to the deformation of the stamped part 12.

[0144] The method for manufacturing a set of two sheets according to the invention may in particular involve overlay welding, as illustrated in Figure 2, otherwise known as overlap welding. It has also been noted that the tendency to crack during welding was significantly less when the stamped part 12 of composition according to the invention was positioned below the flat part 11 during welding, i.e. on the side of the impact of the laser beam. This advantage is obtained in the case of overlay welding. Thus, in an advantageous embodiment, the stamped part 12 of composition according to the invention is positioned on the side of the impact of the laser beam during welding.

[0145] The essential advantage of the invention is the possibility of using a monolithic rolled sheet, having improved weldability, in particular during laser welding, preferably remotely without filler wire, a welding process generally known to those skilled in the art under the name of "Remote Laser Welding", as well as formability and corrosion resistance properties at least comparable to those of the AA6xxx family alloys conventionally used for their high mechanical characteristics.

[0146] Welding techniques, particularly laser welding, of aluminium alloys are described, for example, in ISO 15609-4 (May 2009), ISO 4063 (August 2009) and ISO 13919-2 (January 2021).

[0147] Target applications include the manufacture of heat exchangers such as electric vehicle battery coolers.

[0148] Use

[0149] The invention also relates to a heat exchanger, preferably a battery cooler for an electric vehicle, made at least in part from a set of two sheets according to the present invention.

[0150] The invention also relates to the use of a set of two sheets according to the present invention or obtained according to the present invention, for the manufacture of a heat exchanger, preferably a battery cooler for an electric vehicle.

[0151] Examples

[0152] Example 1: Weldability

[0153] A weldability test using the laser overlap welding method (see Figure 2) of the “Remote Laser Welding” type was carried out on sheets based on three different aluminum alloys: a 6016 type alloy, a 5182 type alloy and an alloy according to the invention. The chemical compositions of these alloys are given in Table 1 below.

[0154] [Table 1]

[0155] The tested sheets were obtained by following the steps described below.

[0156] Manufacturing process for 6016 alloy sheets:

[0157] - casting then scalping to obtain a sheet of approximately 582 mm thick; - reheating to approximately 560°C for approximately 2 hours, then to approximately 530°C for approximately 1 hour;

[0158] - cooling to approximately 415°C;

[0159] - hot rolling to a thickness of approximately 7.3 mm, with a hot rolling start temperature of approximately 415°C and a hot rolling end temperature of approximately 300°C;

[0160] - cold rolling to an intermediate thickness of approximately 4 mm (reduction rate 45%);

[0161] - intermediate annealing at approximately 350°C for approximately 4 hours of holding;

[0162] - cold rolling to a final thickness of approximately 1.01 mm (reduction rate 75%);

[0163] - solution heating at approximately 555°C, with a holding time of approximately 5 seconds above 550°C, then quenching.

[0164] Manufacturing process for type 5182 alloy sheets:

[0165] - casting then scalping to obtain a sheet of approximately 582 mm thick;

[0166] - reheating to approximately 490°C;

[0167] - hot rolling up to a thickness of 2.5 mm, with a hot rolling start temperature of approximately 470°C and a hot rolling end temperature of approximately 330°C;

[0168] - cold rolling to a thickness of approximately 0.9 mm (reduction rate 64%);

[0169] - solution at approximately 385°C, then quenching.

[0170] Method for manufacturing alloy sheets according to the invention:

[0171] - casting then scalping to obtain a sheet of approximately 582 mm thick;

[0172] - homogenization at approximately 500°C for a total duration of approximately 18 hours;

[0173] - hot rolling to a thickness of approximately 3.5 mm, with a hot rolling start temperature of approximately 500°C and a hot rolling end temperature of approximately 340°C;

[0174] - cold rolling to a thickness of approximately 1.04 mm;

[0175] - solution treatment at approximately 550°C, with a holding time of approximately 30 seconds above 530°C, then quenching.

[0176] Two sheets of the same alloy were welded together by overlap (see Figure 2), for each of the three alloys described above. In Figure 2, reference 1 corresponds to a overlap weld, reference 2 corresponds to the first sheet to be welded, and reference 3 corresponds to the second sheet to be welded. The term "overlap" means that the weld completely passes through the first sheet to be welded 2 and that it passes at least partially through the second sheet to be welded 3.

[0177] The quality of the welds obtained was determined following the criteria of EN ISO 13919-2 (January 2021). The quality criteria of EN ISO 13919-2 (January 2021) are illustrated in Figure 3. In Figure 3, reference 1 corresponds to an overlap weld, reference 2 corresponds to the first sheet to be welded, and reference 3 corresponds to the second sheet to be welded, reference 4 corresponds to a channel, reference 5 corresponds to the channel height, reference 6 corresponds to the allowance of weld 1, reference 7 corresponds to the height of allowance 6, reference 8 corresponds to the penetration depth of weld 1, and reference 9 corresponds to the weld width at the interface between sheets 2 and 3 (bead).

[0178] The results obtained are given in Table 2 below.

[0179] [Table 2] According to Table 2 above, the best results were obtained with sheets based on the alloy according to the invention, particularly in terms of visual appearance and cracking.

[0180] Several welding speeds were tested (not all shown in Table 2): 10 m / min (3250 W), 15 m / min (4500 W), 20 m / min (5500 W), 25 m / min (6500 W) and 30 m / min (7500 W), and for all these speeds, the best results were obtained with the sheets based on the alloy according to the invention, particularly in terms of visual appearance and cracking.

[0181] It is worth noting that it was possible to weld at speeds as high as 10 m / min, 15 m / min, 20 m / min, 25 m / min or 30 m / min, while the welding speed is usually around 4 to 5 m / min.

[0182] Example 2: Mechanical performance

[0183] The same alloy according to the invention as that used in Example 1 above was used to measure the mechanical performances according to standard NF EN ISO 6892-1. In addition to a sheet in the metallurgical state T4 obtained by following the process described in Example 1 above, sheets having the metallurgical states T6 and T7 were manufactured by following the processes described below.

[0184] Method for manufacturing an alloy sheet according to the invention in the T6 metallurgical state:

[0185] In addition to the steps described above in Example 1 of the process for manufacturing alloy sheets according to the invention, carry out tempering for approximately 90 minutes at approximately 205°C in an air furnace, hot at the time of introduction of the sheet, then allow to cool in the open air to room temperature.

[0186] Method for manufacturing an alloy sheet according to the invention in the T7 metallurgical state:

[0187] In addition to the steps described above in Example 1 of the process for manufacturing alloy sheets according to the invention, carry out tempering for approximately 200 minutes at approximately 205°C in an air furnace, hot at the time of introduction of the sheet, then allow to cool in the open air to room temperature.

[0188] The mechanical performances obtained are given in Table 3 below.

[0189] [Table 3]

[0190] According to Table 3 above, the mechanical performances obtained are satisfactory for use in the field of heat exchangers, and in particular electric vehicle battery coolers, with in particular an Rp0.2 which can be greater than or equal to 200 MPa. It should also be noted that the mechanical properties of a sheet according to the present invention having the metallurgical state T61 (values ​​not illustrated here) make it possible to propose a sheet having a good compromise between formability and mechanical strength.

[0191] Example 3: Corrosion resistance

[0192] The same alloy according to the invention as that used in Example 1 above was used to measure the corrosion resistance of different sheets. In addition to the sheets having the metallurgical tempers T4, T6 and T7 described in Examples 1 and 2 above, a sheet having the metallurgical temper T61 was manufactured following the method described below. The sheets all had a thickness of approximately 1 mm + / - 0.05 mm.

[0193] Method for manufacturing an alloy sheet according to the invention in the T61 metallurgical state:

[0194] In addition to the steps described above in Example 1 of the process for manufacturing alloy sheets according to the invention, carry out tempering for approximately 30 minutes at approximately 205°C in an air furnace, hot at the time of introduction of the sheet, then allow to cool in the open air to room temperature.

[0195] To determine corrosion resistance, a cyclic SWAAT (Sea Water Acidified Acetic Test) test according to ASTM G85 A3 was carried out on sheets with different metallurgical conditions. The SWAAT test includes alternating 30-minute salt spray phases and 1.5-hour wet phases at a temperature of approximately 49°C.

[0196] The results obtained are as follows:

[0197] - T4 and T61: intergranular corrosion, corrosion depth greater than 30% of the sheet thickness, and some perforations after 40 days of testing;

[0198] - T6: intergranular corrosion and corrosion depth greater than 30% of the sheet thickness, but no perforation after 40 days of testing;

[0199] - T7: no intergranular corrosion, corrosion depth less than 30% of the sheet thickness, and no perforation after 40 days of testing.

[0200] The results therefore show that the sheet having the metallurgical state T7 has better corrosion resistance than the sheets having the metallurgical states T4, T6 and T61.

[0201] Example 4: Environmental Performance / Recyclability

[0202] No detailed analysis of the scraps that can be incorporated into the alloy according to the present invention has been carried out, but it seems at least theoretically possible to incorporate into the present alloy all the scraps that can be incorporated into the AA6xxx series alloys for monolithic automotive body sheets. On the other hand, the present alloy seems to be able to absorb certain primary casting alloys, such as for example A365.1. It should also be noted that the sheet according to the present invention, which is monolithic, i.e. composed of a single alloy, allows all the waste from its life cycle to be recycled within itself, from its manufacture to its recycling at the end of its life. This is a notable advantage compared to multi-clad sheets, common in the field of heat exchangers.

[0203] Example 5: Mechanical performance

[0204] Several alloys according to the invention were used to measure mechanical performance according to standard NF EN ISO 6892-1. The chemical compositions of these alloys are given in Table 4 below.

[0205] [Table 4]

[0206] Manufacturing process of LNV-1 alloy sheet:

[0207] - casting then scalping to obtain a plate of approximately 1820 x 510 x 3900 mm;

[0208] - homogenization at approximately 500°C for a total duration of approximately 10 hours;

[0209] - hot rolling to a thickness of approximately 2.6 mm, with a hot rolling start temperature of approximately 480°C;

[0210] - cold rolling to a thickness of approximately 0.8 mm;

[0211] - solution heating at approximately 550°C, with a holding time of approximately 30 seconds above 530°C, then quenching and winding at approximately 65°C.

[0212] Manufacturing process for LNV-2 to LNV-6 alloy sheets:

[0213] - casting then scalping to obtain a plate approximately 55 mm thick;

[0214] - homogenization at approximately 545°C for a total duration of approximately 12 hours;

[0215] - hot rolling to a thickness of approximately 3.5 mm, with a hot rolling start temperature of approximately 545°C;

[0216] - cold rolling to a thickness of approximately 0.8 mm;

[0217] - solution heating at approximately 545°C, with a holding time of approximately 2 minutes, then quenching; - pre-tempering for approximately 8 hours at approximately 60°C, then cooling in the open air to room temperature.

[0218] The mechanical performances obtained are given in Table 5 below.

[0219] [Table 5]

[0220] According to Table 5 above, it is possible to play on the composition of the alloy in order to vary the mechanical properties according to the desired characteristics (here a compromise between Rm and elongation).

Claims

CLAIMS 1. Set of two sheets assembled, preferably by laser welding, comprising, preferably consisting of: - a stamped part (12), formed from an aluminum alloy having the following composition, in mass percentages: If: from 2.50 to 6.50%, - preferably from 3.0 to 6.0%, preferably from 3.50 to 5.50%, preferably from 4.0 to 5.0%, from 4.25 to 4.75%, - Fe: up to 0.50%, preferably up to 0.40%, preferably up to 0.30%, preferably up to 0.25%; and at least 0.05%, preferably at least 0.10%, preferably at least 0.15%; Cu: up to 0.20%, preferably up to 0.17%, preferably up to 0.15%, preferably up to 0.12%; and preferably at least 10 ppm, preferably at least 20 ppm, preferably at least 40 ppm, preferably at least 60 ppm; Mn: up to 0.40%, preferably up to 0.30%, preferably up to 0.20%; and preferably at least 0.05%, preferably at least 0.08%, preferably at least 0.10%; Mg: from 0.05 to 0.50%, preferably from 0.08 to 0.45%, preferably from 0.10 to 0.40%, preferably from 0.10 to 0.35%, - Cr: from 0.05 to 0.35%, preferably from 0.06 to 0.30%, preferably from 0.08 to 0.25%, preferably from 0.10 to 0.20%, preferably from 0.10 to 0.15%, - Ti: from 0.02 to 0.30%, preferably from 0.04 to 0.25%, preferably from 0.05 to 0.25%, preferably from 0.07 to 0.20%, preferably from 0.10 to 0.20%, - Sr: up to 500 ppm, preferably up to 450 ppm, preferably up to 400 ppm, preferably up to 350 ppm, and preferably at least 50 ppm, preferably at least 100 ppm, preferably at least 150 ppm, preferably at least 200 ppm, preferably at least 250 ppm; unavoidable impurities < 0.05% each and < 0.15% in total, remainder aluminum; and - a flat part (11), formed from an aluminum alloy, preferably the same aluminum alloy as the stamped part (12) or a 6xxx alloy or a 5xxx alloy; the two parts being assembled so as to form a channel (13) thanks to the deformation of the stamped part (12).

2. Set of two sheets according to claim 1, characterized in that it is welded and that the weld between the flat part (11) and the stamped part (12) is continuous. Tl 3. A method of manufacturing a strip, intended to produce a sheet used according to one of the preceding claims, comprising the successive steps of: a. Casting the aluminum alloy according to claim 1 into a plate, preferably by vertical semi-continuous casting; b. Homogenizing the plate, at a homogenization temperature preferably comprised between 490 and 550°C, for a holding time preferably greater than or equal to 2 hours; c. Hot rolling to obtain a strip, the hot rolling start temperature preferably being between 450 and 550°C and the hot rolling end temperature preferably being between 250 and 380°C; d. Cold rolling the strip, with optionally an intermediate anneal, the reduction in thickness of the strip during cold rolling preferably being between 50 and 75%; e. Solution treatment then quenching, preferably in air; f.Optionally pre-tempered, at a pre-tempering temperature preferably of 50 to 120°C, for a period preferably of 2 to 16 hours, preferably obtained by coiling then cooling to room temperature; g. Additional tempering in a batch furnace, with a temperature maintenance for a period of 20 minutes to 24 hours and a metal temperature of 100 to 210°C.

4. Method of manufacturing a sheet metal used as a flat part (11) according to claim 1 or 2, comprising the successive steps of: - manufacturing a strip according to the method of claim 3; - cutting into the desired dimensions.

5. Method of manufacturing a sheet metal used as a stamped part (12) according to claim 1 or 2, comprising the successive steps of: - manufacturing a strip according to the method of claim 3; - cutting into the desired dimensions; - stamping so as to create a channel (13) after assembly between a flat part (11) and a stamped part (12); the cutting and stamping can be carried out in any order.

6. Method of manufacturing a set of two sheets according to any one of claims 1 or 2, comprising the steps of: - supply of two sheets, one of the sheets forming a flat part (11) and the other sheet forming a stamped part (12), respectively manufactured one according to the method of claim 4 and the other according to the method of claim 5; - Assembly of the two flat (11) and stamped (12) parts, preferably by laser welding, preferably remotely without filler wire, preferably by overlapping, so as to form a channel (13) thanks to the deformation of the stamped part (12).

7. Method according to the preceding claim, characterized in that the welding of the two parts is continuous.

8. Heat exchanger, preferably a battery cooler for an electric vehicle, made at least in part from a set of two sheets according to any one of claims 1 or 2.

9. Use of at least one set of two sheets according to any one of claims 1 or 2, or obtained according to the method of claim 6 or 7, for the manufacture of a heat exchanger, preferably a battery cooler for an electric vehicle.

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