EP4087704A1

EP4087704A1 - Method for manufacturing a multilayer aluminium alloy strip or sheet for making brazed heat exchangers

Info

Publication number: EP4087704A1
Application number: EP21704845.3A
Authority: EP
Inventors: Benoît BRUN; Didier MAURIN; Armelle Danielou
Original assignee: Constellium Neuf Brisach SAS
Current assignee: Constellium Neuf Brisach SAS
Priority date: 2020-01-07
Filing date: 2021-01-05
Publication date: 2022-11-16
Also published as: FR3105933B1; FR3105933A1; WO2021140296A1; WO2021140296A9; US20230055410A1

Abstract

Disclosed is a method for manufacturing a multilayer strip or sheet, comprising the consecutive steps of: - casting a brazing aluminum alloy in the form of a cast plate; - sawing the cast plate to obtain sawn brazing alloy layers; - assembling a core aluminum alloy layer with at least one sawn brazing aluminum alloy layer to obtain a multilayer assembly; - preheating the multilayer assembly; - hot-rolling the multilayer assembly to obtain a multilayer strip or sheet, the first hot-rolling pass inducing a reduction in the thickness of the multilayer assembly greater than or equal to 0.5% of the thickness of the multilayer assembly before said hot-rolling pass.

Description

Title: Manufacturing process of a multi-layer aluminum alloy strip or sheet for the manufacture of brazed heat exchangers

Technical area

The present disclosure falls within the field of thin strips or sheets (of thickness generally comprised from 0.05 to 3.5 mm, preferably from 0.15 to 2.5 mm) used for alloy heat exchangers aluminum, and preferably with a core alloy of aluminum-manganese alloy (3xxx series according to the nomenclature of the Aluminum Association), plated on one or both sides with a layer of brazing alloy, preferably with 'aluminum-silicon alloy (4xxx series according to the nomenclature of the Aluminum Association), obtained by sawing and possibly an intermediate alloy, generally placed between the core and the brazing alloy. These strips or sheets are intended in particular for the manufacture of elements, such as tubes, plates and collectors, used in heat exchangers assembled by brazing. These exchangers are found in particular in engine cooling and air conditioning systems in automobile interiors. The techniques for brazing aluminum alloys are described for example in the article by JC Kucza, A. Uhry and JC Goussain "Strong 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 may especially be used in brazing techniques in ovens in a controlled atmosphere CAB (controlled atmosphere brazing) with a flow of for example NOCOLOK ^® kind or without flow, or else in brazing furnaces empty.

Prior art

[0002] The properties required for the strips or sheets of aluminum alloy used for the manufacture of brazed exchangers are in particular sufficient formability for easy shaping of the tubes, plates and collectors, before brazing, good suitability for brazing , high mechanical strength after brazing, and good resistance to corrosion after brazing. Of course, it is important that the alloys chosen are easy to cast and roll and / or co-roll and that the cost of manufacturing the strips or sheets is compatible with the requirements of the automotive industry. During the co-rolling step of multi-layer strips or sheets, it is important to have good cohesion between the different layers of core alloy, brazing alloy and possibly intermediate alloy without there being any blistering formations visible to the naked eye on the surface of strips or sheets.

[0003] It is known in particular from European patents EP 1200253 B2 of Hydro, EP 1 992441 B1 or EP 2428 306 B1, of the manufacturing processes of an aluminum alloy composite material in which a covering alloy layer is clad on at least one side of a core layer and wherein the clad core layer is subjected to multiple rolling passes. In these patents, the cover layer is produced by sawing. EP 1992441 B1 and EP 2428 306 B1 teach the need for high requirements on the surface of sawn cover sheets to obtain "an optimum bond between the core layer and the cover layer". The covering alloy layers are then necessarily subjected to a step of smoothing the surface prior to the rolling step and / or have a roughness Ra of between 0.05 and 1.0 μm. It should be noted that the measurement filters are not specified.

summary

The present disclosure improves the situation.

There is proposed a method of manufacturing a strip or multilayer sheet, comprising a layer of core aluminum alloy plated, on one or both main faces, with an alloy layer of brazing aluminum, characterized in that it comprises the successive steps of: a. casting of a brazing aluminum alloy in the form of a casting plate, preferably having a thickness of 400 to 700 mm, more preferably of 500 to 650 mm; preferably a width of 1500 to 2000 mm, preferably 1600 to 1850 mm; preferably a length of 2500 to 6000 mm, preferably 3000 to 4500 mm; b. optionally, stress relieving of the casting plate by heat treatment; vs. sawing of the casting plate to obtain layers of brazing alloy sawn in a plane parallel to the plane of at least one of the main faces of said casting plate; d. assembly of a layer of core aluminum alloy, which may or may not be homogenized, withat least one layer of sawn brazing aluminum alloy, to obtain a multilayer assembly; e. preheating of the multilayer assembly, preferably to a temperature of 440 to 540 ° C, preferably with a hold at the maximum temperature for less than 30 hours, preferably less than 24 hours, more preferably less than 20 hours, preferably with a duration of temperature rise of less than 24 hours, preferably less than 20 hours, more preferably less than 15 hours; f. hot rolling of the multilayer assembly to obtain a strip or multilayer sheet, the first hot rolling pass inducing a reduction in thickness of the multilayer assembly greater than or equal to 0.5% of the thickness of the multilayer assembly before said hot rolling pass; the thickness of the multilayer strip or sheet obtained after all the hot rolling passes preferably being from 2 to 5.5 mm; g. optionally, cold rolling of the strip or multilayer sheet. to the desired thickness, the thickness of the strip or sheet after cold rolling preferably being 0.15 to 3 mm and h. optionally annealing, preferably at a temperature of 230 to 450 ° C., preferably with a maintenance at the maximum temperature for 1 minute to 15 hours, preferably for 1 minute to 5 hours.

According to another aspect, there is proposed a strip or sheet, intended for the manufacture of brazed heat exchangers, obtained according to the process of the present invention in which the casting plate made of brazing aluminum alloy:

- is not subjected, prior to the sawing step, to homogenization; and

- either is not subjected, prior to the sawing step, to stress relieving, or is subjected, prior to the sawing step, to stress relieving at a temperature below 400 ° C, preferably below 380 ° C , more preferably less than 355 ° C and even more preferably less than or equal to 350 ° C, preferably for a period of less than 10 h, more preferably less than 5 h; the strip or sheet with final thickness before brazing having at least one of the brazing layers which is obtained by sawing and which has a size of the silicon particles with a surface area greater than or equal to 0.011 μm ² (measured in the L-TC plane ) such that the average equivalent diameter of these particles is less than 1.6 µm, preferably less than 1.5 µm, preferably less than 1.4 µm. According to another aspect, there is proposed a heat exchanger produced at least in part from a strip or sheet obtained according to the method of the invention.

According to another aspect, there is proposed 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 corrosion resistance without degradation of the heat exchanger. mechanical strength or solderability with respect to a strip or sheet having an identical configuration but comprising at least one brazing layer obtained by rolling.

[0008] The characteristics set out in the following paragraphs can optionally be implemented. They can be implemented independently of each other or in combination with each other:

[0009] Preferably, the brazing alloy layer or layers represent from 4 to 15%, preferably from 4 to 12% in thickness of the total thickness of the multilayer assembly before any rolling step.

Preferably, the brazing aluminum alloy casting plate is subjected, prior to the sawing step, to stress relieving, preferably thermal, at a temperature below 400 ° C, preferably below 380 ° C, more preferably less than 355 ° C and even more preferably less than or equal to 350 ° C, advantageously for a period of less than 24 hours, preferably less than 10 hours and more preferably still less than 3 hours.

[0011] According to one variant, the casting plate made of brazing aluminum alloy is not subjected, prior to the sawing step, to stress relieving, for example thermal. [0012] Preferably, the multilayer strip or sheet further comprises at least one interlayer aluminum alloy layer placed between the core aluminum alloy layer and a brazing layer of an aluminum alloy.

Preferably, the core alloy layer is subjected to a homogenization step prior to the plating step, preferably at a temperature of 560 to 630 ° C, preferably for 10 minutes to 18 hours.

According to one variant, the core alloy layer is not subjected to a homogenization step prior to the plating step.

Preferably, the brazing alloy layer is made of 4xxx alloy, preferably of an alloy chosen from the alloys AA4045, AA4343, AA4004 and AA4104, more preferably in an alloy (for example 4xxx, AA4045, AA4343, AA4004 and / or AA4104) comprising an amount of Zn less than 0.05% by mass.

Preferably, the brazing alloy layer has, after sawing and before rolling, a surface roughness as defined in standard NF EN ISO 4287 of December 1998:

- Ra less than 14 μm, preferably less than 11 μm, preferably less than 10 μm and preferably greater than 1 μm, preferably greater than 2 μm, preferably greater than 5 μm, measured with a Gaussian filter of 0, 8 mm wavelength in the direction perpendicular to the saw cuts; and or

- Ra less than 50 μm, preferably less than 40 μm, more preferably less than 32 μm, even more preferably less than 20 μm, and preferably greater than 3 μm, preferably greater than 5 μm, preferably greater than 15 μm, measured with a Gaussian filter of 8 mm wavelength in the direction perpendicular to the saw cuts; and or

- Rt less than 250 μm, preferably less than 200 μm, preferably less than 180 μm and preferably greater than 25 μm, preferably greater than 30 μm, preferably greater than 50 μm, measured with a Gaussian filter of 0, 8 mm wavelength in the direction perpendicular to the saw cuts; and or

- Rt less than 400 μm, preferably less than 350 μm, more preferably less than 280 μm, and preferably greater than 15 μm, preferably greater than 35 μm, measured with a Gaussian filter of 8 mm wavelength in the direction perpendicular to the saw cuts.

Preferably, the core alloy layer comprises, in percentages by weight:

- Si: at most 0.8%, preferably at most 0.6%, more preferably at most 0.5%; and even more preferably at most 0.25%;

- Fe: at most 0.5%, preferably at most 0.4%, more preferably at most 0.3%;

- Cu: from 0.20 to 1.2%, preferably from 0.25 to 1.1%, more preferably from 0.3 to 1.0%, even more preferably from 0.5 to 0.8%, even more preferably from 0.55 to 0.75%;

- Mn: from 0.8 to 2.2%, preferably from 0.9 to 2.1%, more preferably from 1.0 to 2.0%, even more preferably from 1.0 to 1.5%, even more preferably from 1.25 to 1.45%;

- Mg: at most 0.6%, preferably at most 0.35%, more preferably at most 0.20%, even more preferably less than 0.05%;

- Zn: at most 0.30%, preferably at most 0.25%, more preferably at most 0.20%, and even more preferably less than 0.05%;

- Ti: at most 0.30%, preferably at most 0.25%, more preferably at most 0.20%, even more preferably at most 0.14%, and even more preferably at most 0.12%; preferably at least 0.05%;

- remainder of aluminum and impurities.

Brief description of the figures

Other characteristics, details and advantages will become apparent on reading the detailed description below and on analyzing the appended figures.

[0019] [Fig. 1] is a photo showing the sample used for the example soldering tests.

[0020] [Fig. 2] is a diagram describing the perforation analysis during the corrosion resistance test of the examples.

Description of the embodiments

In the context of the present description, the following definitions should be specified.

Unless otherwise stated, all indications concerning the chemical composition of the alloys are expressed as a percentage by weight based on the weight of the alloy. The designation of the alloys is made in accordance with the rules of the Aluminum Association. The definitions of metallurgical states are given in European standard EN 515.

In the present application, the terms "controlled atmosphere" mean an atmosphere having a majority gas, for example nitrogen or argon, and having a limited amount of O 2, preferably comprising less than 150 ppm, more preferably less than 100 ppm, even more preferably less than 50 ppm, and even more preferably less than 20 ppm of oxygen.

According to one embodiment, the present invention relates to a method of manufacturing a strip or multilayer sheet. The strip or multilayer sheet comprises a layer of core aluminum alloy plated, on one or both main faces, with a layer of brazing aluminum alloy, preferably of type 4xxx and comprises optionally one or two aluminum alloy layers interposed between the core aluminum alloy layer and the brazing aluminum alloy layer. After assembly of the various layers and before lamination, we speak of multilayer assembly. After rolling the multilayer assembly, a multilayer strip or sheet is obtained.

Multilayer tape or sheet

The strip or multilayer sheet is obtained by rolling, hot and optionally cold, of the multilayer assembly. The total thickness of the strip or sheet is advantageously from 0.05 to 3.5 mm, preferably from 0.15 to 2.5 mm, more preferably from 0.18 to 1 mm.

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

The configuration with two layers comprises a plated core with a brazing layer on one side only.

The configuration with three layers includes:

- Either a core layer plated on both sides with a brazing layer;

- Either a core layer plated on a single face with an intermediate layer and a brazing layer;

- Or a core layer plated on a first face with a brazing layer and on the other face with a protective layer to improve corrosion resistance, for example made of lxxx, 3xxx or 7xxx type alloy.

The configuration with four layers includes:

- Either a core layer plated on a first face with an intermediate layer and a brazing layer and on the other face with a brazing layer;

- either a core layer plated on a first face with an intermediate layer and a brazing layer and on the other face with a protective layer to improve corrosion resistance, for example made of an alloy of type lxxx, 3xxx or 7xxx. Optionally, the protective layer can be obtained by sawing.

The configuration with five layers comprises a core layer plated on both sides with an interlayer and a brazing layer.

Core Aluminum Alloy According to one embodiment, the core aluminum alloy layer is made of a 3xxx type alloy.

According to one embodiment, the core layer has been obtained by sawing.

According to one embodiment, the core aluminum alloy layer comprises, in percentage by weight,:

- Fe: at most 0.5%, preferably at most 0.4%, more preferably at most 0.3%;

- remainder of aluminum and impurities.

The composition limits of the base alloy used as the core can be justified as follows. A limited iron content is favorable to corrosion resistance and to formability, but it is not necessary to go down to very low contents (for example <0.10%) which would lead to high cost prices. Copper is a hardening element which contributes to the mechanical resistance, but above 1.2%, coarse intermetallic compounds can be formed on casting which adversely affect the homogeneity of the metal and constitute sites of initiation of corrosion, or cracks in the tray during casting. Manganese contributes to mechanical strength. A limited addition of zinc can have a beneficial effect on corrosion resistance, by modifying the electrochemical potentials, especially for alloys with the highest copper content. However, it must remain below 0.3% to avoid too high a susceptibility to generalized corrosion.

Aluminum alloy brazing

According to an advantageous embodiment, the brazing alloy layer or layers represent from 4 to 15%, preferably from 4 to 12% in thickness of the total thickness of the multilayer assembly before rolling.

According to a preferred embodiment, the brazing aluminum layer is made from an alloy of the 4xxx family, preferably from an alloy chosen from the alloys AA4045, AA4343, AA4004 and AA4104, more preferably from an alloy (for example 4xxx, AA4045, AA4343, AA4004 and / or AA4104) comprising an amount of Zn less than 0.05% by mass.

Aluminum alloy interlayer

According to one embodiment, the strip or multilayer sheet further comprises at least one intermediate aluminum alloy layer placed between the core aluminum alloy layer and a brazing aluminum alloy layer. .

According to one embodiment, the interlayer has been obtained by sawing.

Preferably, the intermediate aluminum alloy of the strip or sheet according to the present invention is of the 3xxx or lxxx type, for example AA3003, AA3207 or AA1050, more preferably of the 3xxx type, for example AA3003 or AA3207.

By way of illustration, the intermediate aluminum alloy of the strip or sheet according to the present invention can comprise (% by mass):

- AA3003: less than 0.6% Si; less than 0.7% Fe; from 0.05 to 0.20% Cu; from 1.0 to 1.5% Mn; less than 0.10% Zn, impurities less than 0.05% each and less than 0.15% in total; remains Al; or

- AA3207: less than 0.30% Si; less than 0.45% Fe; less than 0.10% Cu; from 0.40 to 0.8% Mn; less than 0.10% Mg; less than 0.10% Zn, impurities less than 0.05% each and less than 0.15% in total; remains Al; or

- AA1050: less than 0.25% Si; less than 0.40% Fe; less than 0.05% Cu; less than 0.05% Mn; less than 0.05% Mg; less than 0.05% Zn, less than 0.03% Ti; less than 0.05% V; impurities less than 0.03% each; at least 99.50% Al.

Preferably, the intermediate aluminum alloy of the strip or sheet according to the present invention comprises (% by mass): Si <0.25%, preferably <0.18%; Fe <0.2%; Cu <0.1%; Mn from 0.6 to 0.8%; Mg <0.02%; other elements <0.05% each and <0.15% in total, remainder aluminum.

Manufacturing process of a strip or multilayer sheet

The method according to the present invention comprises the successive steps of: a. casting of a brazing alloy in the form of a casting plate, preferably having a thickness of 400 to 700 mm, more preferably of 500 to 650 mm; preferably a width of 1500 to 2000 mm, preferably 1600 to 1850 mm; preferably a length of 2500 to 6000 mm, preferably 3000 to 4500 mm; b. optionally, stress relieving of the casting plate by heat treatment; vs. sawing of the casting plate to obtain layers of brazing alloy sawn in a plane parallel to the plane of at least one of the main faces of said casting plate; d. assembling a layer of core aluminum alloy, which may or may not be homogenized, with at least one sawn brazing aluminum alloy layer to obtain a multilayer assembly; e. preheating of the multilayer assembly, preferably to a temperature of 440 to 540 ° C, preferably with a hold at the maximum temperature for less than 30 hours, preferably less than 24 hours, more preferably less than 20 hours, preferably with a duration of temperature rise of less than 24 hours, preferably less than 20 hours, more preferably less than 15 hours; f. hot rolling of the multilayer assembly to obtain a strip or multilayer sheet, the first hot rolling pass inducing a reduction in thickness of the multilayer assembly greater than or equal to 0.5% of the thickness of the assembly multilayer before said hot rolling pass; the thickness of the multilayer strip or sheet after all the hot rolling passes preferably being 2 to 5.5 mm; g. optionally, cold rolling of the strip or multilayer sheet. to the desired thickness, the thickness of the strip or sheet after cold rolling preferably being 0.15 to 3 mm and h. optionally annealing, preferably at a temperature of 230 to 450 ° C., preferably with a maintenance at the maximum temperature for 1 minutes to 15 hours, preferably for 1 minutes to 5 hours. Before the assembly of step d), the core alloy is generally cast in the form of a casting plate. This plateau is generally scalped on at least the two main faces.

According to the present invention, the brazing aluminum alloy layer is cast and then sawn in a plane parallel to the plane of at least one of the main faces of said brazing alloy layer. The sawing step is carried out on one, preferably the two main faces of the brazing aluminum alloy layer. Reducing the thickness of the brazing layer by sawing rather than rolling has many advantages. In particular, the manufacturing process is simplified and has a lower manufacturing cost. However, if such a sawing step is known from the prior art, it is in no way specified in the prior art how to avoid the formation of visible blisters on the surface of the final strip or sheet. On the other hand, according to certain documents of the prior art presented above, this sawing step is necessarily followed by a surface preparation step, in particular a polishing step in order to reduce the surface roughness of the layer. and allow good cohesion of the layers of the strip or multilayer sheet during the co-rolling step. Cleaning after sawing does not constitute a surface preparation step and is therefore not excluded from the present invention.

Completely surprisingly, the method of the present invention makes it possible to dispense with such a step of preparing the surface of the sawn brazing layer and in particular a polishing step. Thus, at the end of the sawing step, the brazing alloy layer may have, according to a roughness measurement after sawing and before rolling, a maximum difference between peaks and valleys over a length of 150 mm in the direction perpendicular to the saw cuts of less than 0.55 mm and preferably less than 0.3 mm.

According to an embodiment compatible with the previous one, the brazing alloy layer may have, after sawing and before rolling, a surface roughness as defined in standard NF EN ISO 4287 of December 1998:

- Ra less than 50 pm, preferably less than 40 pm, more preferably less at 32 mih and more preferably less than 20 μm, and preferably greater than 3 μm, preferably greater than 5 μm, preferably greater than 15 μm, measured with a Gaussian filter of 8 mm wavelength in the perpendicular direction saw cuts; and or

- Rt less than 400 μm, preferably less than 350 μm, more preferably less than 280 μm, and preferably greater than 15 μm, preferably greater than 35 μm, measured with a Gaussian filter of 8 mm wavelength in the direction perpendicular to the saw cuts

The roughness profile after sawing and before rolling of the brazing alloy layers was measured with a perthometer, over a distance of 150 mm, in the direction perpendicular to the saw cuts. The start and end of the profile have been removed (12.5 mm on each side). The profile was straightened with a second degree polynomial. The maximum-minimum difference between peaks and valleys was deduced from this. The values of Ra and Rt as defined in standard NF EN ISO 4287 of December 1998 were then calculated with two Gaussian filters of respective wavelength 0.8 mm and 8 mm over a distance of 125 mm. The roughness Ra (in pm) is the arithmetic mean of the profile. The roughness Rt (in pm) is the total height of the roughness profile.

The sawn brazing alloy layer is then plated on the core aluminum alloy layer to obtain a multilayer assembly. Optionally, at least one interlayer aluminum alloy layer is placed between the brazing alloy layer and the core alloy layer.

According to an advantageous embodiment, the brazing aluminum alloy casting plate is subjected, prior to the sawing step, to stress relieving, preferably thermal, at a temperature below 400 ° C, preferably less than 380 ° C, more preferably less than 355 ° C and even more preferably less than or equal to 350 ° C, advantageously for a period of less than 24 hours, preferably less than 10 hours and more preferably still less than 3 hours. According to another embodiment, the casting plate, prior to the sawing step, is on the contrary not subjected to stress relieving.

According to one embodiment, the core alloy layer is subjected to a homogenization step prior to the plating step, preferably at a temperature of 560 to 630 ° C, preferably for 10 minutes at 18 hours. According to another embodiment, the casting plate made of brazing aluminum alloy is preferably not subjected to a homogenization step prior to the sawing step. Likewise, according to another embodiment, the brazing alloy layer is preferably not subjected to a homogenization step prior to the plating step.

The multilayer assembly comprising a sawn brazing alloy layer is subjected to a specific hot rolling step making it possible to dispense with the step of surface preparation of the sawn brazing alloy layer. Thus, the first hot rolling pass of the multilayer assembly induces a reduction in thickness of the multilayer assembly greater than or equal to 0.5% of the thickness of the multilayer assembly before said hot rolling pass. Surprisingly, such a hot rolling step allows good cohesion between the different layers of core alloy, brazing alloy and possibly intermediate alloy without there being any visible blistering. on the surface of the strip or sheet, even when the brazing alloy layer (s) have not undergone surface preparation such as polishing prior to plating. Preferably, the total thickness of the strip or sheet after all the hot rolling passes is preferably 2 to 5.5 mm.

Optionally, the strip or multilayer sheet is subjected to a cold rolling step following that of hot rolling, in order to obtain a strip or sheet of the desired final thickness. The thickness of the strip or sheet after cold rolling is preferably 0.15 to 3 mm.

According to one embodiment, the strip or multilayer sheet can then be subjected to an annealing step, preferably at a temperature of 230 to 450 ° C. Advantageously, the maximum annealing temperature is maintained for 1 minute to 15 hours, preferably for 1 minute to 5 hours.

The strip or sheet according to the invention can be used for the manufacture of different parts of a heat exchanger, for example tubes, plates, collectors, etc. More particularly, the strip or sheet obtained according to the present invention is intended for the manufacture of brazed heat exchangers.

The strip or sheet obtained according to the method of the present invention advantageously comprises at least one brazing layer obtained by sawing and of which the average equivalent diameter of the silicon particles with a surface area greater than or equal to 0.011 μm ² (measured in the plane L-TC) is less than 1.6 µm, preferably less than 1.5 µm, preferably less than 1.4 µm. The average equivalent diameter of the silicon particles is obtained by image analysis from photographs taken with an optical microscope at magnification x50 in the plane [(rolling direction) x (short transverse direction)]. It should be noted that the short transverse direction corresponds to the thickness of the strip or sheet. The minimum particle surface area analyzed is 0.011 µm ² , measured in the L-TC plane. From the total area of each particle, an equivalent diameter is defined, which corresponds to that of a circular particle with the same area. Then an average is carried out with all the determined equivalent diameters.

The present inventors have in particular demonstrated a non-degradation, or even an improvement in the corrosion resistance of the strips or sheets comprising such brazing layers.

Another subject of the invention is a heat exchanger produced at least in part from a strip or sheet according to the present invention.

A subject of the invention is also 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 corrosion resistance without degradation of the resistance. mechanical or solderability with respect to a strip or sheet having an identical configuration but comprising at least one brazing layer obtained by rolling.

The strips or sheets according to the present invention can be used in the manufacture of radiators, in particular of automobiles, such as engine cooling radiators, oil radiators, heating radiators and air coolers. supercharging, as well as in air conditioning systems (especially evaporators and condensers), and battery cooling in the case of electric vehicles.

Examples Example 1

Industrial tests were carried out as follows:

Two AA4045 brazing alloys (see the compositions in Table 1 below, in percentages by weight) were cast in the form of a plate 560 mm thick. The AA4045 alloy trays were sawn on both sides in a plane parallel to one of the main sides of the tray, in layers 64mm thick each. Prior to the sawing step, the plates of tests 4 to 6 were not subjected to stress relieving while those of tests 1 to 3 were subjected to stress relieving by heating at 350 ° C. for 2 hours. [0062] [Table 1]

Multilayer assemblies were formed by assembling a layer of core alloy (see the compositions Alloy A and Alloy C in Table 1 above, in percentages by mass) of thickness 480-540 mm and a layer AA4045 brazing alloy (see compositions 4045-1 and 4045-2 in Table 1 above, in percentages by weight). The brazing alloy was AA4045-1 for tests 1 to 5 and AA4045-2 for test 6. The core alloy was Alloy A for tests 1 to 5 and Alloy C for test 6 The thickness of the multilayer assemblies before rolling is detailed in Table 2 below. The core alloy layer was scalped prior to the assembly step. None of the layers of the assembly have been homogenized. The assembly was preheated to a temperature of 480 to 520 ° C with a total time of 13 to 27 hours (see Table 2 below) and a temperature rise time of less than 15 hours, then hot rolled to 'to 2-3 mm of total thickness. The reduction in thickness of the first hot rolling pass is detailed in Table 2 below. Hot-rolled assemblies made it possible to obtain multilayer strips which were then subjected to cold rolling to a total thickness of 0.24 mm. The rolled strips were finally subjected to an annealing step at a temperature of 250-320 ° C for a holding time of less than 12 hours, the final strip was in a H24 metallurgical state.

The roughness profile after sawing and before rolling of the AA4045 brazing alloy layers was measured with a perthometer, over a distance of 150 mm, in the direction perpendicular to the saw cuts. The start and end of the profile have been removed (12.5 mm on each side). The profile was straightened with a second degree polynomial. The maximum-minimum difference between peaks and valleys was deduced from this. The values of Ra and Rt as defined in standard NF EN ISO 4287 of December 1998 were then calculated with two Gaussian filters of respective wavelengths 0.8 mm and 8 mm over a distance of 125 mm. The roughness Ra (in pm) is the arithmetic mean of the profile. The roughness Rt (in pm) is the total height of the roughness profile. The maximum-minimum difference, Ra and Rt are reported in Table 2 below.

The presence of blisters after hot rolling at the surface of the multilayer strip was evaluated by observing the strips with the naked eye after hot rolling. A blister corresponds to a blistering of the metal due to an internal detachment at the interface between the brazing layer and the layer below said brazing layer, and is of a dimension greater than 1 mm in the direction of rolling. The result of this evaluation is presented in Table 2 below. [0066] [Table 2]

It is observed that there are no blisters when the first hot rolling pass results in a reduction in thickness greater than 2 mm (Tests 1, 4 and 5: 5 mm and Test 6: 3 mm ). The average equivalent diameter of the silicon particles with a surface area greater than or equal to 0.011 μm ² (measured in the L-TC plane) was measured after final annealing according to the method described above in [0056] for 2 samples: the one corresponding to the configuration of Test 1 and for an almost identical configuration except that the brazing layer was hot rolled and not sawn before assembly with the core layer. In the case of the configuration with the sawn solder layer, the average equivalent diameter of silicon particles with a surface area greater than or equal to 0.011 µm ² (measured in the L-TC plane) was 1.37 µm. In the case of the configuration with the rolled solder layer, the average equivalent diameter of silicon particles with a surface area greater than or equal to 0.011 µm ² (measured in the L-TC plane) was 1.74 µm. Example 2 The brazing quality was analyzed using mini prototypes with different amounts of brazing flux.

Two configurations of multilayer bands were tested:

- Strips comprising a layer of AA4045-1 brazing alloy representing 10% in thickness of the total thickness of the strip and a core layer of Alloy A (see Table 1 of Example 1) in the metallurgical state H24 and 0.24 mm thick; and

- strips comprising two layers of AA4045-1 brazing alloy, each representing 10% in thickness of the total thickness of the strip, placed on each of the two main faces of a core layer of Alloy B (see Table 1 of Example 1) in the H24 metallurgical state and 0.4 mm thick.

Said bands were obtained according to the following process:

- casting of a brazing alloy AA4045-1 in the form of a casting plate 560 mm thick;

- Obtaining a brazing alloy layer by: either stress relieving the casting plate for 2 hours at 350 ° C then sawing on the two main faces; either hot rolling;

- assembly of the layers to obtain a multilayer assembly according to the configurations described above and in Table 4 below;

- preheating the assembly to a temperature of 480 to 520 ° C with a total time of 13 to 27 hours and a temperature rise time of less than 15 hours;

- hot rolling of the assembly up to 2-3 mm total thickness, with a reduction in thickness of the first rolling pass of 5 mm, to obtain a multilayer strip;

- cold rolling of the strip to a total thickness of 0.24 mm or 0.41 mm;

- annealing of the strip at a temperature of 250-320 ° C for a holding time of less than 10 hours. The final strip was in a H24 metallurgical condition.

The two configurations are summarized in Table 4 below.

[0073] [Table 4]

Each configuration was then tested from the point of view of its brazing quality, according to the following protocol, which makes it possible to simulate the brazing of stamped parts. To do this, sheets of 50 mm x 60 mm were cut from the multilayer strips and then stamped to add two longitudinal lines as shown in Figure 1. After stamping, the sheets were degreased with an acetone solution and then air-dried. Each stamped sheet was then attached to a flat sheet having the same composition as the stamped sheet, which was previously flattened using a press. The two sheets were fixed together using stainless steel pins, as shown in Figure 1. In Figure 1, Reference 1 corresponds to a stamped sheet, reference 2 to a flat sheet, reference 3 to two stamped lines and the reference 4 with pins. The sheets thus assembled were brazed with 5 g / m ² of Nocolok ^® flow under an atmosphere having an amount of oxygen maintained at less than 25 ppm. The brazing cycle was as follows:

- first temperature rise to about 575-580 ° C with a ramp of about 25 ° C / min;

- second temperature rise to about 600 ° C with a ramp of about 2.5 ° C / min;

- hold for 3 minutes at 600 ° C +/- 2 ° C;

- cooling down to about 400 ° C with a ramp of about 25 ° C / min.

The length of each brazing joint was then measured. For each configuration, three samples were taken. For each sample, two measurements were made at the two stamped longitudinal lines. The configurations tested as well as the results of the brazing test are presented in Table 5 below.

The length of the seal for the Conf.l to Conf.4 configurations is presented in Table 5 below.

[0077] [Table 5]

Brazing is just as good for sawn brazing layers as it is for rolled brazing layers.

Example 3

Samples Conf.l 'to Conf.4' were prepared under the same conditions as the samples Conf.l to Conf.4 of Example 2 above, except that the brazing was carried out without flux on A4 formats placed in a vertical position in the brazing furnace. Corrosion resistance was determined using the following protocol:

- prepare for each configuration a sample of dimensions 126 mm (L direction) x 90 mm (TL direction), previously degreased with white absorbent paper soaked in acetone;

- protect the untested face as well as the four edges over a width of approximately 0.5 cm with a transparent vinyl adhesive (for example of the 3M vinyl 764 type);

- clean the face to be tested with absorbent paper soaked in acetone:

- place the samples thus prepared on a rack with an inclination of about 60 ° from the horizontal;

- Carry out for each sample a SWAAT (Sea Water Acidified Acetic Test) cyclic test according to the ASTM G85 A3 standard, comprising in particular an alternation of fog phases of 30 min and of wet phases of 1h30 at a temperature of 49 ° C.

The number of piercings was recorded each day for each sample throughout the duration of the test, ie 3 or 9 days. The piercings were visible on the back of each sample as they blistered in the adhesive applied to the untested face, as shown in Figure 1. In Figure 2, the reference 6 corresponds to the sample; reference 7 corresponds to the adhesive; the reference 8 corresponds to a perforation; reference 9 corresponds to a blister formed by a perforation. The results of the monitoring of the number of piercings are presented in Table 6 below.

[0082] [Table 6] The corrosion resistance of bands comprising a sawn brazing alloy layer is at least as good as that of bands comprising a rolled brazing alloy layer, and even improved after 3 days for thin bands (about 240 μm ) and 9 days for thick bands (around 410 µm).

Claims

[Claim 1] A method of manufacturing a multilayer strip or sheet, comprising a layer of plated core aluminum alloy, on one or both main faces, with a layer of brazing aluminum alloy , characterized in that it comprises the successive steps of: a. casting of a brazing aluminum alloy in the form of a casting plate, preferably having a thickness of 400 to 700 mm, more preferably of 500 to 650 mm; preferably a width of 1500 to 2000 mm, preferably 1600 to 1850 mm; preferably a length of 2500 to 6000 mm, preferably 3000 to 4500 mm; b. optionally, stress relieving of the casting plate by heat treatment; vs. sawing of the casting plate to obtain layers of brazing alloy sawn in a plane parallel to the plane of at least one of the main faces of said casting plate; d. assembling a layer of core aluminum alloy, which may or may not be homogenized, with at least one sawn brazing aluminum alloy layer to obtain a multilayer assembly; e. preheating of the multilayer assembly, preferably to a temperature of 440 to 540 ° C, preferably with a hold at the maximum temperature for less than 30 hours, preferably less than 24 hours, more preferably less than 20 hours, preferably with a duration of temperature rise of less than 24 hours, preferably less than 20 hours, more preferably less than 15 hours; f. hot rolling of the multilayer assembly to obtain a strip or a multilayer sheet, the first hot rolling pass inducing a reduction in thickness of the multilayer assembly greater than or equal to 0.5% of the thickness of the multilayer assembly before said hot rolling pass; the thickness of the multilayer strip or sheet after all the hot rolling passes preferably being 2 to 5.5 mm; g. optionally, cold rolling of the strip or multilayer sheet. to the desired thickness, the thickness of the strip or sheet after cold rolling preferably being 0.15 to 3 mm and h. optionally annealed, preferably at a temperature of 230 to 450 ° C, preferably with a maintenance at the maximum temperature for 1 minute to 15 hours, preferably for 1 minute to 5 hours.

[Claim 2] A method of manufacturing a strip or multilayer sheet according to claim 1, in which the brazing alloy layer (s) represent from 4 to 15%, preferably from 4 to 12% in thickness of the total thickness of the multilayer assembly before any rolling step.

[Claim 3] A method of manufacturing a multi-layered strip or sheet according to any one of the preceding claims, wherein the brazing aluminum alloy casting plate is subjected, prior to the sawing step, to stress relief. at a temperature less than 400 ° C, preferably less than 380 ° C, more preferably less than 355 ° C and even more preferably less than or equal to 350 ° C, advantageously for a period of less than 24 hours, preferably less than 10 hours and more preferably still less than 3 hours.

[Claim 4] A method of manufacturing a multi-layer strip or sheet according to any one of claims 1 or 2, wherein the aluminum alloy brazing casting plate is not subjected, prior to the step of sawing, to a stress relieving.

[Claim 5] A method of manufacturing a multi-layered strip or sheet according to any preceding claim, wherein the multi-layered strip or sheet further comprises at least one intermediate aluminum alloy layer placed between the aluminum alloy layer. core aluminum and a brazing layer of an aluminum alloy.

[Claim 6] A method of manufacturing a multilayer strip or sheet according to any one of the preceding claims, in which the core alloy layer is subjected to a homogenization step prior to the plating step, preferably at a temperature of 560 to 630 ° C, preferably for 10 minutes to 18 hours.

[Claim 7] A method of manufacturing a multilayer strip or sheet according to any one of claims 1 to 5, wherein the core alloy layer is not subjected to a homogenization step prior to the process. plating step.

[Claim 8] A method of manufacturing a strip or multilayer sheet according to any one of the preceding claims, in which the brazing alloy layer is made from 4xxx alloy, preferably from an alloy chosen from alloys AA4045, AA4343, AA4004 and AA4104, more preferably in an alloy (for example 4xxx, AA4045, AA4343, AA4004 and / or AA4104) comprising an amount of Zn less than 0.05% by mass.

[Claim 9] A method of manufacturing a multilayer strip or sheet according to any one of the preceding claims, in which the brazing alloy layer has, after sawing and before rolling, a surface roughness as defined in the standard. NF EN ISO 4287 of December 1998:

- Ra less than 14 μm, preferably less than 11 μm, preferably less than 10 μm and preferably greater than 1 μm, preferably greater than 2 μm, measured with a Gaussian filter with a wavelength of 0.8 mm in the direction perpendicular to the saw cuts; and or

- Ra less than 50 μm, preferably less than 40 μm, more preferably less than 32 μm, even more preferably less than 20 μm, and preferably greater than 3 μm, preferably greater than 5 μm, measured with a Gaussian filter of 8 mm wavelength in the direction perpendicular to the saw cuts; and or

- Rt less than 250 μm, preferably less than 200 μm, preferably less than 180 μm and preferably greater than 25 μm, preferably greater than 30 μm, measured with a Gaussian filter of 0.8 mm wavelength in the direction perpendicular to the saw cuts; and or

[Claim 10] A method of manufacturing a multilayer strip or sheet according to any one of the preceding claims wherein the core alloy layer comprises, in percentages by weight:

- Fe: at most 0.5%, preferably at most 0.4%, more preferably at most 0.3%;

- remainder of aluminum and impurities.

[Claim 11] Strip or sheet, intended for the manufacture of brazed heat exchangers, obtained according to the method of at least one of claims 1 to 10, in which the casting plate made of brazing aluminum alloy:

- is not subjected, prior to the sawing step, to homogenization; and

- either is not subjected, prior to the sawing step, to stress relieving, or is subjected, prior to the sawing step, to stress relieving at a temperature below 400 ° C, preferably below 380 ° C , more preferably less than 355 ° C and even more preferably less than or equal to 350 ° C, preferably for a period of less than 10 h, more preferably less than 5 h; the strip or sheet with final thickness before brazing having at least one of the layers of brazing which is obtained by sawing and which has a size of the silicon particles with a surface greater than or equal to 0.011 μm ² (measured in the L-TC plane) such that the average equivalent diameter of these particles is less than 1.6 μm, preferably less than 1.5 µm, more preferably less than 1.4 µm.

[Claim 12] Heat exchanger produced at least in part from a strip or sheet obtained according to the process of any one of claims 1 to 10.

[Claim 13] Use of a strip or sheet according to claim 11, for the manufacture of a heat exchanger, said strip or sheet exhibiting improved corrosion resistance without degradation of mechanical strength or solderability with respect to a strip or sheet having an identical configuration but comprising at least one brazing layer obtained by rolling.