Aluminum alloy strip or sheet for the manufacture of brazed heat exchangers

Description

TECHNICAL FIELD

[0001] The invention relates to thin strips or sheets (generally of thickness from 0.05 to 3 mm, preferably from 0.15 to 2.5 mm) of aluminum-manganese core alloy (series 3xxx according to the Aluminum Association nomenclature), optionally plated on one or two faces with a covering alloy, most often an aluminum-silicon brazing alloy (series 4xxx according to the Aluminum Association nomenclature) and / or an interlayer alloy, placed between the core and the possible brazing alloy, of aluminum-manganese alloy (series 3xxx according to the Aluminum Association nomenclature).These strips or sheets are primarily intended for the manufacture of components, such as tubes, manifolds, and plates, for brazed heat exchangers, particularly for the automotive industry, including engine cooling radiators, evaporators, heater cores and charge air coolers, manifolds, battery coolers for electric vehicles, and air conditioning systems. These exchangers are found in engine cooling and cabin air conditioning systems for automobiles. Brazing techniques for aluminum alloys are described, for example, in the article by JC Kucza, A. Uhry, and JC Goussain, "Hard Brazing of Aluminum and its Alloys," published in Soudage et Techniques Connexes, Nov.-Dec. 1991, pp. 18-29.The strips or sheets according to the invention can in particular be used in brazing techniques with non-corrosive flux of the NOCOLOK ®< type or CAB (controlled atmosphere brazing). EARLIER ART

[0002] The properties required for aluminum alloy strips or sheets used in the manufacture of brazed heat exchangers include sufficient formability for easy shaping of tubes, collector fins, and plates before brazing; good brazing properties; high mechanical strength after brazing, allowing for the use of the thinnest possible thicknesses; good resistance to fatigue stress in service; and good corrosion resistance after brazing. Naturally, it is important that the chosen alloy be easy to cast and roll, and that the manufacturing cost of the strips or sheets be compatible with the requirements of the automotive industry.

[0003] In order to promote the reduction of tube thickness for heat exchangers (such as radiators), it is particularly advantageous to increase the mechanical properties of the material after brazing (in particular the maximum load (Rm) of the tensile curve obtained according to ISO 6892-1 (“ Ultimate Tensile Strength " Or " UTS (in English), which is a key factor in fatigue resistance), without reducing corrosion resistance or brazingability.

[0004] Solutions have already been proposed in this regard. Examples include the following patent applications, which disclose the compositions listed below: WO2020 / 178507: 0.1 - 0.3% Si; <0.2% Fe; 0.75 - 1.05% Cu; 1.2 - 1.7% Mn; <0.03% Mg; <0.15% Ti; <0.1% Zn; EP1183151: 0.4 - 0.8% Si; <0.4% Fe; 0.5 - 2% Cu; 0.5 - 1.5% Mn; EP2017032: 0.3 - 1.2% Si; 0.05 - 0.4% Fe; 0.3 - 1.2% Cu; 0.3 - 1.8% Mn; 0.05 - 0.6% Mg; <0.3% Ti; <0.3% Zr; <0.3% Cr. US2018 / 043476: 0.5 - 1.8% Mn; 0.05 - 1.3% If; 0.05 - 0.5% Fe; 0.05 - 0.5% Mg; 0.05 - 0.3% Zr; 0.05 - 0.3% Ti and 0.05 - 0.3% Cr.

[0005] However, the proposed solutions do not necessarily allow for the right compromise between good mechanical strength after brazing, good corrosion resistance and good brazingability.

[0006] Faced with growing market demand, there remains a need for a new core alloy with improved mechanical strength compared to existing alloys, without compromising corrosion resistance or brazingability. Such a core alloy could meet the ongoing demand for reduced product thickness. DESCRIPTION OF THE INVENTION

[0007] Surprisingly, the applicant has identified a composition range that improves mechanical strength without degrading corrosion resistance or brazingability.

[0008] As an example, the target according to the present invention may be to achieve a tensile strength Rm greater than 140 MPa, preferably greater than 145 MPa, preferably greater than 150 MPa, preferably greater than 160 MPa for industrial strips or sheets after brazing.

[0009] As demonstrated in the examples, the present invention also has the unexpected advantage of improving corrosion resistance, for example, corrosion in the SWAAT test. The invention thus relates to a strip or sheet, intended for the manufacture of brazed heat exchangers, having a core layer, optionally a cover layer on one or two faces of the core layer, and optionally an interlayer on one or two faces of the core layer placed between the core layer and the optional cover layer, the core layer being made of aluminum alloy of composition (% by mass) according to claim 1.

[0010] The invention also relates to a method for manufacturing a strip or sheet according to claim 8.

[0011] The invention also relates to a heat exchanger according to claim 9.

[0012] The invention also relates to the use of a strip or sheet according to claim 10. FIGURES

[0013] [ Fig. 1 ] There Figure 1 is a diagram describing the perforation analysis during the SWAAT corrosion resistance test of the examples. DETAILED DESCRIPTION OF THE INVENTION

[0014] In the description and claims, unless otherwise stated: The designation of aluminium alloys conforms to the nomenclature of The Aluminium Association; the contents of chemical elements are designated as mass percentages. Core aluminum alloy

[0015] The strip or sheet according to the present invention is intended for the manufacture of brazed heat exchangers, and has a core layer, optionally a cover layer on one or two faces of the core layer and optionally an interlayer layer on one or two faces of the core layer placed between the core layer and the optional cover layer, the core layer being made of aluminum alloy of composition (% by mass):Si: more than 0.25%, preferably more than 0.30%, preferably more than 0.35%, preferably more than 0.40%; and less than 0.60%, preferably less than 0.55%; Fe: less than 0.25%, preferably less than 0.20%; and at least 0.08%, preferably more than 0.10%; Cu: more than 0.60%, preferably more than 0.70%, preferably more than 0.80%, preferably more than 0.85%; and less than 1.10%, preferably less than 1.00%, preferably less than 0.95%; Mn: more than 1.40%, preferably more than 1.50%; and less than 2.00%, preferably less than 1.80%, preferably less than 1.65%; Ti: less than 0.10%; and more than 0.05%; Mg: less than 0.05%, preferably less than 0.02%, preferably less than 0.01%, preferably less than 0.001%; ​​Zr: less than 0.01%, preferably less than 0.005%; Cr: less than 0.01%, preferably less than 0.005%; Zn: less than 0.20%, preferably less than 0.10%, preferably less than 0.05%, preferably less than 0.01%;Impurities: less than 0.05% each and less than 0.15% in total; remainder is aluminum.

[0016] The compositional limits of the core alloy can be justified in the following way.

[0017] A minimum silicon content of 0.10% avoids the need for a costly pure base. It has been observed that silicon contents above 0.25% improve corrosion resistance, for example, in SWAAT tests. Therefore, the silicon content is preferably above 0.25%, preferably above 0.30%, preferably above 0.35%, and preferably above 0.40%.

[0018] Excessive silicon content can lower the core solidus temperature and compromise the solder joint. It is best to limit silicon to less than 0.60%, preferably less than 0.55%.

[0019] An iron content limited to less than 0.25%, preferably less than 0.20%, is also beneficial for corrosion resistance and formability, particularly by reducing the fraction of coarse precipitates containing iron. However, it is not necessary to go down to very low levels, for example, below 0.08%, which would lead to high production costs. Therefore, the iron content is greater than or equal to 0.08%, preferably greater than 0.10%.

[0020] Copper is a hardening element that contributes to mechanical strength, but above 1.1%, the risk of cracking during casting is higher. Coarse intermetallic compounds can also form during casting, impairing the metal's homogeneity and potentially creating corrosion initiation sites. To achieve high mechanical strength, the copper content should be greater than 0.60%, preferably greater than 0.70%, preferably greater than 0.80%, and preferably greater than 0.85%. Preferably, the copper content should be less than 1.10%, preferably less than 1.00%, and preferably less than 0.95%.

[0021] Manganese contributes to mechanical strength through solid solution and the formation of Al-Mn-Si dispersoids. For significant hardening, the manganese content is preferably greater than 1.40%, and preferably greater than 1.50%. To avoid the formation of a large number of coarse phases during casting, which can reduce formability, it is recommended to limit the Mn content to less than 2.00%, preferably less than 1.80%, and preferably less than 1.65%.

[0022] A limited addition of zinc can have a beneficial effect on corrosion resistance by modifying electrochemical mechanisms, particularly for alloys with high copper content. However, it must remain below 0.20% to avoid excessive susceptibility to generalized core corrosion. Preferably, the zinc content is limited to less than 0.10%, preferably less than 0.05%, and preferably less than 0.01%.

[0023] Magnesium provides a significant increase in mechanical strength. However, in the case of controlled atmosphere furnace (CAB) brazing with flux, it is preferable to limit its content to less than 0.2%. According to the present invention, the magnesium content is less than 0.05%, preferably less than 0.02%, preferably less than 0.01%, and preferably less than 0.001%.

[0024] Titanium allows for control of grain size during casting. Its content is less than 0.10%. The Ti content is greater than 0.05%.

[0025] Zirconium and chromium may be added optionally. However, they are preferably absent, or present at a level corresponding to impurities, i.e. less than 0.01%, preferably less than 0.005% each. Aluminum alloy cover

[0026] The strips or sheets according to the present invention generally have a thickness of 0.05 to 3 mm, preferably 0.15 to 2.5 mm, depending on the type of part manufactured, and can be plated, on one or two faces of the core layer and / or on a free face of the possible interlayer, with a covering alloy, which can be either a brazing alloy, or an alloy playing the role of sacrificial anode to protect the part from corrosion, such as an alloy containing zinc, for example of the 7xxx series, preferably comprising from 0.70 to less than 2.50%, preferably from 0.70 to less than 1.30%, preferably from 0.70 to less than 1.00% Zn, or for example of the 3xxx series, preferably comprising from 0.50 to 1.60%, preferably from 0.90 to 1.20% Zn. The alloy in the 7xxx series could, for example, be the AA7072 alloy.The free face of any interlayer corresponds to the face of the interlayer that is not in contact with the core layer. It should be noted that a brazing layer can be bonded to one or two faces of a core layer and / or to the free face of an interlayer, whereas the sacrificial anode can preferably be bonded to only one or two faces of a core layer, without an interlayer between the core layer and the sacrificial anode.

[0027] According to one embodiment, a sacrificial anode type cover alloy could be, according to the present invention, an alloy of the 7xxx series, preferably having the following composition, in mass percentages: less than 0.50% Si; less than 0.50% Fe; less than 0.25% Cu; less than 0.30% Mn; less than 0.20%, preferably less than 0.15% Mg; from 0.70 to 5.00%, preferably from 0.70 to less than 2.50%, preferably from 0.70 to less than 1.30%, preferably from 0.70 to less than 1.00% Zn; less than 0.15% Ti; other elements less than 0.05% each and less than 0.15% in total; remainder aluminum.

[0028] As an example, composition AA7072 is an aluminum alloy suitable for use as a sacrificial anode according to the present invention. Its composition, in mass percentages, is: less than 0.05% Si; less than 0.05% Fe; less than 0.10% Cu; less than 0.10% Mn; less than 0.10% Mg; 0.80 to 1.30% Zn; other elements less than 0.05% each and less than 0.15% in total; the remainder being aluminum.

[0029] According to one variant, the AA7072 composition preferably comprises less than 1.00% of Zn.

[0030] According to another variant, a sacrificial anode type cover alloy could be, according to the present invention, an alloy of the 3xxx series, preferably having the following composition, in mass percentages: from 0.10 to 0.35% Si; less than 0.70% Fe; less than 0.20% Cu; from 0.70 to 2.00%, preferably from 0.90 to 1.30% Mn; from 0.50 to 1.60%, preferably from 0.90 to 1.20% Zn; less than 0.15% Ti; other elements less than 0.05% each and less than 0.15% total; remainder aluminum.

[0031] Preferred values ​​of each of the elements of the 3xxx series or 7xxx series alloys, which could be suitable as a sacrificial anode according to the present invention, are given by way of example in Table 1 below (columns 3xxx-1, 7xxx-1 and 7xxx-2), in mass percentages. [Table 1] 3xxx-1 7xxx-1 7xxx-2 If 0,10 - 0,35 % 0,05 - 0,30 % 0,15-0,40 % Fe < 0,70 % 0,25 - 0,45 % < 0,40 % Cu < 0,20 % < 0,15 % < 0,15 % Mn 0,7 - 1,30 % < 0,15 % < 0,10 % Mg < 0,05 % < 0,05 % < 0,10 % Cr < 0,05 % < 0,05 % < 0,05 % Neither < 0,05 % < 0,05 % < 0,05 % Zn 0,9 - 1,55 % 0,80 - 1,30 % 3,50 - 4,50 % Preferred to be 0.80 to < 1% Ti < 0,10 < 0,10 % < 0,10 % Preferred < 0.05% Preferred < 0.05% Preferred < 0.05% Zr < 0,05 % < 0,05 % < 0,05 %

[0032] The brazing alloy is preferably a 4xxx series alloy, preferably containing less than 0.20%, preferably less than 0.10%, preferably less than 0.05%, preferably less than 0.02% zinc, with a liquidus temperature sufficiently low relative to the solidus of the core alloy to provide a sufficient temperature range for brazing, acceptable mechanical strength, and good wettability. These alloys may contain alloying elements, for example strontium, preferably in a mass fraction of less than 0.05%.

[0033] According to one embodiment, the brazing alloy of the present invention comprises Y, Sn, and / or Bi. This embodiment is particularly advantageous for fluxless brazing. Preferably, the brazing alloy comprises: from 0.01 to 0.10%, preferably from 0.015 to 0.08%, preferably from 0.02 to 0.065% of Y; from 0.01 to 0.10%, preferably from 0.015 to 0.08%, preferably from 0.02 to 0.065% of Sn; and / or at most 0.04%, preferably at most 0.03%, preferably at most 0.02% of Bi according to a first variant; or at most 0.15%, preferably at most 0.12%, and preferably at least 0.05% of Bi according to a second variant.

[0034] Preferably, the strip or sheet according to the present invention is plated on one or two faces of the core layer and / or on a free face of a possible interlayer with a brazing aluminum alloy, preferably an alloy of the 4xxx series comprising from 4.00 to 13.00% by mass of Si, less than 1.00% by mass of Fe, and preferably less than 0.20%, preferably less than 0.10%, preferably less than 0.05%, preferably less than 0.02% of Zn.

[0035] Preferably, the 4xxx series brazing aluminum alloy comprises (% by mass): Si: from 5.00 to 13.00%, preferably from 6.00 to 11.00%, preferably from 7.50 to 10.50%; Fe: less than 0.60%, preferably less than 0.50%, preferably less than 0.30%; Cu: less than 0.40%, preferably less than 0.10%, preferably less than 0.05%; Mn: less than 0.20%, preferably less than 0.10%, preferably less than 0.05%; Mg: according to a first variant less than 0.20%, preferably less than 0.10%, preferably less than 0.05%; or according to a second variant from 0.50 to 2.50%, preferably from 1.00 to 2.00%; Zn: less than 0.20%, preferably less than 0.10%, preferably less than 0.05%, preferably less than 0.02%; Ti: less than 0.30%, preferably less than 0.10%, preferably less than 0.05%; possibly Bi, Y, Sr and / or Sn; other elements: less than 0.05% each and less than 0.15% in total; remainder aluminum.

[0036] As an example, composition AA4045 is an aluminum alloy that can be suitable as a brazing alloy according to the present invention. Its composition is, in mass percentage: from 9.0 to 11.0% Si, less than 0.80% Fe, less than 0.30% Cu, less than 0.05% Mn, less than 0.05% Mg, less than 0.10% Zn, less than 0.20% Ti, other elements less than 0.05% each and less than 0.15% in total, the remainder being aluminum.

[0037] For example, the preceding composition preferably comprises less than 0.60% Fe. For example, the preceding composition preferably comprises less than 0.10% Cu. For example, composition AA4343 is an aluminum alloy suitable as a brazing alloy according to the present invention. Its composition, by mass percentage, is: 6.80 to 8.20% Si, less than 0.80% Fe, less than 0.25% Cu, less than 0.10% Mn, less than 0.05% Mg, other elements less than 0.05% each and less than 0.15% in total, the remainder being aluminum.

[0038] For example, the preceding composition preferably comprises less than 0.30% Fe. For example, the preceding composition preferably comprises less than 0.10% Cu. For example, composition AA4004 is an aluminum alloy suitable as a brazing alloy according to the present invention. Its composition, by mass percentage, is: 9.00 to 10.50% Si, less than 0.80% Fe, less than 0.25% Cu, less than 0.10% Mn, 1.00 to 2.00% Mg, less than 0.20% Zn, other elements less than 0.05% each and less than 0.15% in total, the remainder being aluminum.

[0039] As an example, composition AA4104 is an aluminum alloy that can be suitable as a brazing alloy according to the present invention. Its composition is, in mass percentage: from 9.00 to 10.50% Si, less than 0.80% Fe, less than 0.25% Cu, less than 0.10% Mn, from 1.00 to 2.00% Mg, less than 0.20% Zn, from 0.02 to 0.20% Bi, other elements less than 0.05% each and less than 0.15% in total, the remainder being aluminum. Aluminum alloy interlayer

[0040] According to one embodiment, the strip or sheet according to the present invention is plated, on one or two faces of the core layer, with an interlayer aluminum alloy, preferably from the 1xxx or 3xxx series, placed between the core and the possible brazing alloy, preferably comprising (by mass percentage): Si: less than 0.50%, more preferably less than 0.20%; Fe: less than 0.70%, more preferably less than 0.30%, even more preferably less than 0.20%; Mn: from 0.30 to 1.40%, more preferably from 0.50 to 0.90%, more preferably from 0.60 to 0.80%, or according to a variant from 1.00 to 1.30%; Cu: less than 0.30%, preferably less than 0.10%, even more preferably less than 0.05%; possibly Mg, Zn and / or In; other elements < 0.05% each and < 0.15% in total; remainder aluminum.

[0041] Preferably, the aluminum alloy interlayer of the strip or sheet according to the present invention comprises (% by mass): Si < 0.15%; Fe < 0.20%; Cu < 0.10%; Mn from 0.60 to 0.80%; Mg < 0.02% according to a first variant or Mg < 0.50%, preferably < 0.25% according to a second variant; other elements < 0.05% each and < 0.15% in total, remainder aluminum.

[0042] Preferably, the interlayer aluminum alloy is an alloy from the AA3xxx series.

[0043] According to one variant, the interlayer aluminum alloy may also include: Zn with a content of 1.5 to 2.3%; and / or In with a content of 0.005 to 0.04%. Strip or sheet metal

[0044] The strip or sheet according to the present invention is a so-called brazing strip or sheet, which can be used to manufacture different parts of a heat exchanger, for example tubes, plates, collectors, battery cooling systems for electric vehicles, etc.

[0045] The strip or sheet according to the present invention can have a configuration with several layers, and in particular with 2, 3, 4 or 5 layers.

[0046] The two-layer configuration includes a core plated on one side with a cover layer, specifically either with a brazing layer or with a sacrificial anode.

[0047] The three-layer configuration includes: either a core layer plated on both sides with a brazing layer; or a core layer plated on both sides with a sacrificial anode; or a core layer plated on one side with an intercalated layer, itself plated with a brazing layer; or a core layer plated on one side with a brazing layer and on the other side with a sacrificial anode.

[0048] The four-layer configuration includes: either a core layer plated on one face with an intercalated layer, itself plated with a brazing layer, and on the other face with a brazing layer; or a core layer plated on one face with an intercalated layer, itself plated with a brazing layer, and on the other face with a sacrificial anode.

[0049] The five-layer configuration includes a core layer plated on both sides with an interlayer layer itself plated with a brazing layer.

[0050] In each of the configurations mentioned above, when two brazing layers, two interlayers, or two sacrificial anodes are used, they may be identical or different in terms of composition and thickness. In particular, the thickness of each of the layers other than the core layer—that is, the brazing layer, the interlayer, and the sacrificial anode—is preferably 4 to 15%, and preferably 4 to 11%, of the total thickness of the strip or sheet according to the present invention. Preferably, the composition of the sacrificial anodes is identical. Process

[0051] The invention also relates to a method for manufacturing a strip or sheet, comprising the successive steps of: casting of a core alloy plate; optionally homogenizing the plate from 550 to 630°C, preferably from 580 to 630°C for 1 to 24 hours; optionally plating with a covering aluminum alloy on one or two faces of the core layer and optionally an interlayer aluminum alloy on one or two faces of the core layer; preheating to a temperature of 450 to 550°C, preferably with holding at maximum temperature for less than 30 hours, preferably for less than 20 hours, preferably for less than 12 hours, more preferably for less than 3 hours; hot rolling of the optionally homogenized and optionally plated plate at a temperature of 420 to 530°C to a thickness of 2 to 6 mm;cold rolling to the desired thickness, the thickness of the strip or sheet after cold rolling preferably being 0.15 to 3 mm and annealed at a temperature of 240 to 450°C, preferably 240 to 400°C, preferably 280 to 370°C, with holding at the maximum temperature for 10 minutes to 15 hours, preferably 20 minutes to 3 hours.

[0052] The said covering alloy of the processes according to the present invention may in particular be a brazing alloy, or a sacrificial anode, or two brazing alloys, or two sacrificial anodes, or a brazing alloy and a sacrificial anode.

[0053] Preferably, there is no intermediate annealing in the processes according to the present invention. When intended for parts requiring significant shaping, the strip or sheet can be used in the annealed condition (condition O) by performing a final anneal at a temperature of 300 to 450°C, in a continuous or batch furnace. In a batch furnace, the annealing is preferably at a temperature of 325 to 400°C, preferably 330 to 400°C. This annealing improves formability.

[0054] In other cases, it can be used in the work-hardened or restored state, which leads to better mechanical resistance, for example an H14 or H24 state (according to the NF EN 515 standard), the latter state being obtained by a restoration annealing at a temperature of 250 to 325°C, preferably less than 310°C.

[0055] Before installing any plating materials, the core alloy plate can be homogenized at a temperature between 550 and 630°C, preferably between 580 and 630°C. This homogenization improves the ductility of the rolled strip or sheet and is recommended when the strip or sheet is used in the 0 state. It promotes the coalescence of the Mn dispersoids. Use

[0056] The invention also relates to a heat exchanger made at least partly from a strip or sheet according to the present invention.

[0057] The invention also relates to the use of a strip or sheet according to the present invention, for the manufacture of a heat exchanger, said strip or sheet having improved mechanical resistance without degradation of corrosion resistance or brazing.

[0058] The strips or sheets according to the present invention can be used in the manufacture of brazed heat exchangers, particularly for automobiles, such as engine cooling radiators, evaporators, heater cores and charge air coolers, manifolds, battery coolers for electric vehicles, as well as in air conditioning systems. EXAMPLES Example 1

[0059] Various core ingots were cast using vertical semi-continuous casting (DC casting) with aluminium alloys having the compositions given in Table 2 below, in mass percentages: [Table 2] Alloys If Fe Cu Mn Ti T solidus (°C) Reference 0,18 0,16 0,64 1,34 0,08 638 Soul-Comparative-1 0,19 0,18 0,95 1,38 0,08 632 Soul-Comparative-2 0,19 0,18 0,97 1,67 0,08 632 Ame-Innov-1 0,49 0,17 0,66 1,58 0,09 636 Ame-Innov-2 0,49 0,17 0,94 1,57 0,10 631

[0060] The core ingots were then bonded, on one side only, with a brazing plating of AA4045 alloy (9.71% Si; 0.2% Fe; <0.05% Cu; <0.05% Mg; <0.05% Mn; <0.05% Sr; 0.02% Ti) representing 7.5% of the total assembly thickness. The assembly was preheated for 12 hours at 500°C, hot-rolled at approximately 490°C, and then cold-rolled from 4 mm to 0.4 mm. A final annealing for 1 hour at 320°C achieved a H24 metallurgical state.

[0061] Brazing simulations were then carried out on 21 cm x 30 cm samples to reproduce the conditions of controlled atmosphere brazing (CAB) with less than 50 ppm of O2, with heating at 600°C for 2 minutes.

[0062] Tensile strength measurements at different temperatures (20°C, 110°C and 130°C) and corrosion resistance according to the SWAAT test on the plated face were carried out on the brazed samples.

[0063] Tensile strength measurements were carried out according to ISO 6892-1.

[0064] Corrosion resistance was determined using the following protocol: Prepare for each configuration a sample measuring 126 mm (L direction) x 90 mm (TL direction), previously degreased with a white absorbent paper soaked in acetone; protect the untested face and the four edges over a width of approximately 0.5 cm with transparent vinyl tape (for example, 3M vinyl 764); clean the face to be tested with an absorbent paper soaked in acetone; place the samples thus prepared on a rack with an inclination of approximately 60° to the horizontal; perform for each sample a cyclic SWAAT (Sea Water Acidified Acetic Test) according to the ASTM G85 A3 standard, including an alternation of 30 min salt spray phases and 1h30 wet phases at a temperature of 49°C.

[0065] The number of perforations was recorded daily for each sample throughout the 13-day test period. The perforations were visible on the back of each sample as they formed blisters in the adhesive applied to the untested side, as illustrated in the image. Figure 1 In the Figure 1 , reference 6 corresponds to the sample; reference 7 corresponds to the adhesive; reference 8 corresponds to a perforation; reference 9 corresponds to a blister formed by a perforation.

[0066] The results of monitoring the number of perforations are given in Table 3 below. [Table 3] Alloys Rm after brazing 400 µm (MPa) Number of perforations after SWAAT test 20°C 110°C 130°C 13 days Reference 150 150 150 14 Soul-Comparative-1 160 174 166 100 Soul-Comparative-2 169 178 156 74 Ame-Innov-1 166 179 171 9 Ame-Innov-2 161 167 168 7

[0067] In addition to the information given in Table 3 above, the corrosion morphology was determined for each alloy, based on microscopic observations after the SWAAT test: Comparison-1: deep pitting; Comparison-2: deep pitting; Innov1: better than the reference, because the depth of corrosion was less than that of the reference; Innov2: better than the reference, because the depth of corrosion was less than that of the reference.

[0068] Based on Table 3 above, the following conclusions can be drawn: The present invention makes it possible to obtain better mechanical resistances than the reference alloy; the present invention makes it possible to obtain at least the same level of performance in terms of corrosion resistance and susceptibility to perforation after a SWAAT test as the reference alloy. Example 2

[0069] Various core ingots were cast using vertical semi-continuous casting (DC casting) with aluminium alloys having the compositions given in Table 4 below, in mass percentages: [Table 4] Alloys If Fe Cu Mn Ti T solidus (°C) Soul-Comparative-3 0.2 0.13 0.64 1.33 0.08 638 Soul-Comparative-4 0.19 0.12 0.62 1.28 0.08 638 Soul-Comparative-5 0.18 0.12 0.93 1.52 0.08 634 Ame-Innov-3 0.45 0.15 0.93 1.52 0.08 632

[0070] The core ingots were homogenized at a temperature of 550 to 630°C for 1 to 24 hours.

[0071] The core ingots were then bonded with a brazing plating of AA4045 alloy on one side, representing 5% of the total assembly thickness, and with a sacrificial anode of AA7072 alloy on the other side, representing 10% of the total assembly thickness. The compositions of the brazing alloys and sacrificial anodes are given in Table 5 below, as mass percentages. [Table 5] Alloys If Fe Cu Mn Ti Zn Brazing-1 9.83 0.13 0.01 0.01 0.02 0.003 Brazing-2 9.73 0.19 0.01 0.02 0.03 0.003 Brazing-3 9.73 0.19 0.01 0.02 0.03 0.003 Brazing-4 9.73 0.19 0.01 0.02 0.03 0.003 Anode-1 0.14 0.32 0.001 0.003 0.03 0.97 Anode-2 0.15 0.33 0.001 0.003 0.03 0.98 Anode-3 0.15 0.33 0.001 0.003 0.03 0.98 Anode-4 0.15 0.33 0.001 0.003 0.03 0.98

[0072] The brazing alloy and sacrificial anode #1 were plated onto the core of Comparative Core 3 (Assembly 1). The brazing alloy and sacrificial anode #2 were plated onto the core of Comparative Core 4 (Assembly 2). The brazing alloy and sacrificial anode #3 were plated onto the core of Comparative Core 5 (Assembly 3). The brazing alloy and sacrificial anode #4 were plated onto the core of Innovative Core 3 (Assembly 4).

[0073] The assemblies were preheated to a temperature of 450 to 550°C, held at the maximum temperature for less than 30 hours, hot-rolled at a temperature of approximately 500°C to a thickness of 3 mm, then cold-rolled to a final total thickness of 1 mm for the sandwich. A final annealing for 30 minutes at 340°C resulted in a metallurgical state O.

[0074] Brazing simulations were then carried out on 21 cm x 30 cm samples to reproduce the conditions of controlled atmosphere brazing (CAB) with less than 50 ppm of O2, with heating at 600°C for 2 minutes.

[0075] Tensile strength measurements (UTS = Rm), yield strength measurements (TYS = Rp 0.2), and elongation measurements (E% = A%) were performed on the samples before and after brazing. Corrosion resistance measurements using the SWAAT test were performed on the brazed samples on the face plated with the AA4045 brazing alloy.

[0076] The measurements of tensile strength UTS (=Rm), yield strength TYS (=Rp 0.2) and elongation E% (=A%) were carried out according to ISO 6892-1.

[0077] The results of the mechanical performance measurements before and after brazing are given in Table 6 below. [Table 6] Assembly Before brazing After brazing TYS UTS E% TYS UTS E% 1 53 135 26,7 47 136 28,2 2 50 135 28,6 46 135 27,3 3 57 150 30,4 52 152 24,7 4 53 145 25,5 51 150 25,4

[0078] Corrosion resistance was determined using the following protocol: Prepare for each configuration a sample measuring 126 mm (L direction) x 90 mm (TL direction), previously degreased with a white absorbent paper soaked in acetone; protect the untested face and the four edges over a width of approximately 0.5 cm with transparent vinyl tape (for example, 3M vinyl 764); clean the face to be tested with an absorbent paper soaked in acetone; place the samples thus prepared on a rack with an inclination of approximately 60° to the horizontal; perform for each sample a cyclic SWAAT (Sea Water Acidified Acetic Test) according to the ASTM G85 A3 standard, including an alternation of 30 min salt spray phases and 1h30 wet phases at a temperature of 49°C.

[0079] In parallel, the number of perforations was recorded daily for each sample throughout the SWAAT test period, i.e., 29 days, 41 days, 58 days, and 63 days. The perforations were visible on the back of each sample because they formed blisters in the adhesive applied to the untested side, as illustrated in the Figure 1 .

[0080] The results of monitoring the number of perforations are given in Table 7 below. [Table 7] Number of perforations after SWAAT test Assembly 29 days 41 days 58 days 63 days 1 6 4 27 131 2 0 1 6 55 3 0 16 48 113 4 0 0 0 0

[0081] According to Tables 6 and 7 above, it is possible to conclude that the present invention makes it possible to obtain the best compromise between satisfactory mechanical resistances, in particular Rm (=UTS) greater than 140 MPa, and improved corrosion resistance, for example an absence of perforations due to corrosion for a longer period.

Claims

1. A strip or sheet, intended for the manufacture of brazed heat exchangers, having a core layer, optionally a covering layer on one or two face(s) of the core layer and optionally an interlayer on one or two face(s) of the core layer placed between the core layer and the optional covering layer, the core layer being made of an aluminum alloy with the following composition (% by weight): - Si: more than 0.25%, preferably more than 0.30%, preferably more than 0.35%, preferably more than 0.40%; and less than 0.60%, preferably less than 0.55%; - Fe: less than 0.25%, preferably less than 0.20%; and at least 0.08%, preferably more than 0.10%; preferably more than 0.85%; and less than 1.10%, preferably less than 1.00%, preferably less than 0.95%; - Mn: more than 1.40%, preferably more than 1.50%; and less than 2.00%, preferably less than 1.80%, preferably less than 1.65%; - Ti: less than 0.10%; and more than 0.05%; - Mg: less than 0.05%, preferably less than 0.02%, preferably less than 0.01%, preferably less than 0.001%; - Zr: less than 0.01%, preferably less than 0.005%; - Cr: less than 0.01%, preferably less than 0.005%; - Zn: less than 0.20%, preferably less than 0.10%, preferably less than 0.05%, preferably less than 0.01%; - impurities: less than 0.05% each and less than 0.15% in total; - remainder aluminum.

2. The strip or sheet according to claim 1, characterized in that it is plated, over one or two face(s) of the core layer and / or over a free face of the optional interlayer, with a covering alloy which is a brazing aluminum alloy, preferably a 4xxx series alloy comprising from 4.00 to 13.00% by weight of Si, less than 1.00% by weight of Fe, and preferably less than 0.20%, preferably less than 0.10%, preferably less than 0.05%, preferably less than 0.02% Zn.

3. The strip or sheet according to claim 2, characterized in that the 4xxx series brazing aluminum alloy comprises (% by weight): - Si: from 5.00 to 13.00%, preferably from 6.00 to 11.00%, preferably from 7.50 to 10.50; - Fe: less than 0.60%, preferably less than 0.50%, preferably less than 0.30%; - Cu: less than 0.40%, preferably less than 0.10%, preferably less than 0.05%; - Mn: less than 0.20%, preferably less than 0.10%, preferably less than 0.05%; - Mg: according to a first variant less than 0.20%, preferably less than 0.10%, preferably less than 0.05%; or according to a second variant from 0.50 to 2.50%, preferably from 1.00 to 2.00%; - Zn: less than 0.20%, preferably less than 0.10%, preferably less than 0.05%, preferably less than 0.02%; - Ti: less than 0.30%, preferably less than 0.10%, preferably less than 0.05%; - optionally Bi, Y, Sr and / or Sn with Bi: at most 0.04%, preferably at most 0.03%, more preferably at most 0.02%; Y: from 0.01% to 0.10%, preferably from 0.015% to 0.08%, more preferably from 0.02% to 0.065%; Sn: from 0.01% to 0.10%, preferably from 0.015% to 0.08%, more preferably from 0.02% to 0.065%; - other elements: less than 0.05% each and less than 0.15% in total; - remainder aluminum.

4. The strip or sheet according to claim 1, characterized in that it is plated, over one or two face(s) of the core layer, with a covering alloy of the sacrificial anode type, which is a 7xxx series alloy, preferably having the following composition, in weight percentages: - less than 0.50% Si; - less than 0.50% Fe; - less than 0.25% Cu; - less than 0.30% Mn; - less than 0.20%, preferably less than 0.15% Mg; - from 0.70 to 5.00%, preferably from 0.70 to less than 2.50%, preferably from 0.70 to less than 1.30%, preferably from 0.70 to less than 1.00% Zn; - less than 0.15% Ti; - other elements less than 0.05% each and less than 0.15% in total; - remainder aluminum.

5. The strip or sheet according to claim 1, characterized in that it is plated, over one or two face(s) of the core layer, with a covering alloy of the sacrificial anode type, which is a 3xxx series alloy, preferably having the following composition, in weight percentages: - from 0.10 to 0.35% Si; - less than 0.70% Fe; - less than 0.20% Cu; - from 0.70 to 2.00%, preferably from 0.90 to 1.30% Mn; - from 0.50 to 1.60%, preferably from 0.90 to 1.20% Zn; - less than 0.15% Ti; - other elements less than 0.05% each and less than 0.15% in total; - remainder aluminum.

6. The strip or sheet according to claim 2 or 3, characterized in that it is plated, over one or two face(s) of the core layer, with a so-called interlayer aluminum alloy, preferably of the 1xxx or 3xxx series, placed between the core and the brazing alloy, preferably comprising (in weight percentages): - Si: less than 0.50%, more preferably less than 0.20%; - Fe: less than 0.70%, more preferably less than 0.30%, even more preferably less than 0.20%; - Mn: from 0.30 to 1.40%, more preferably from 0.50 to 0.90%, more preferably from 0.60 to 0.80%; or according to one variant from 1.00 to 1.30%; - Cu: less than 0.30%, preferably less than 0.10%, even more preferably less than 0.05%; - optionally Mg, Zn and / or In; - other elements < 0.05% each and < 0.15% in total; - remainder aluminum.

7. The strip or sheet according to claim 6, characterized in that the interlayer aluminum alloy comprises (% by weight): - Si < 0.15%; - Fe < 0.20%; - Cu < 0.10%; - Mn from 0.60 to 0.80%; - Mg < 0.02% according to a first variant or Mg < 0.50%, preferably < 0.25% according to a second variant; - other elements < 0.05% each and < 0.15% in total, - remainder aluminum.

8. A method for manufacturing a strip or sheet according to any one of the preceding claims, comprising the successive steps of: - casting a plate made of a core alloy; - optionally homogenizing the plate at 550 to 630°C, preferably at 580 to 630°C for 1 to 24 hours; core layer and optionally an interlayer aluminum alloy over one or two face(s) of the core layer; the maximum temperature for less than 30 hours, preferably for less than 20 hours, preferably for less than 12 hours, more preferably for less than 3 hours; - hot rolling the optionally homogenized and optionally plated plate at a temperature from 420 to 530°C up to a thickness of 2 to 6 mm, - cold rolling to the desired thickness, the thickness of the strip or sheet after cold rolling preferably being 0.15 to 3 mm, and - annealing at a temperature from 240 to 450°C, preferably from 240 to 400°C, preferably from 280 to 370°C, with maintenance at the maximum temperature for 10 minutes to 15 hours, preferably for 20 minutes to 3 hours.

9. A heat exchanger made at least partially from a strip or sheet according to any one of claims 1 to 7.

10. A use of a strip or sheet according to any one of claims 1 to 7, for the manufacture of a heat exchanger.