HK1191678A - Alloys for a heat exchanger tube having an inner protective cladding and brazed disrupter - Google Patents

Description

Alloy for heat exchanger tubes with internal protective cladding and brazed turbulators

Technical Field

The present invention relates to brazing sheets for heat exchanger tubes made of aluminum alloy, particularly those used for cooling or optimizing engine efficiency, and passenger compartment thermal and air conditioning.

This is particularly applicable to heat exchanger tubes that are subjected to severe corrosive environments, such as charge air cooler (charge air cooler) tubes that perform exhaust gas recirculation, and which typically have turbulators designed to improve heat exchange by increasing exchange surface area and disrupting internal fluid circulation.

Background

Aluminum alloys are used for the manufacture of most automotive heat exchangers due to their low density, which enables weight reduction, especially compared to copper alloys, while having good thermal conductivity, ease of use and good corrosion resistance.

All Aluminum alloys referred to below are named using the names defined by the Aluminum Association in the periodically published Registration Record Series, unless otherwise specified.

The exchanger comprises tubes and fins or baffles for internal fluid circulation and may comprise turbulators to improve the heat transfer between the internal fluid and the external fluid, and it is made by mechanical assembly or by brazing.

In the case of charge air coolers, known to those skilled in the art as CAC, core plates (commonly referred to as tube strips) configured as constituent tubes, typically made of an AA3xxx aluminum alloy, are coated on the outer and inner surfaces with an alloy, commonly known as a braze alloy, of the AA4 xxx-series. This has the advantage that: which melts at a temperature below the melting point of the core and, by applying a thermal brazing cycle, can create a connection between the two materials to be assembled (in other words, be brazed), or can join a tube strip to itself to close the tube by brazing, another option being welding.

This configuration is shown in fig.1, with the core of the tube strip being referred to as designation 2 and the inner and outer braze alloy cladding being referred to as designation 1. The separators placed between the different tube rows consist of uncoated AA3xxx alloys. Similarly, the turbulators inserted into the tubes may also be made of AA3xxx alloys and be unclad. The insert is brazed to the tube by a4xxx cladding on the outer surface of the tube. The turbulators are brazed into the tube by a4xxx cladding on the inner surface of the tube. The AA3xxx alloys used for the baffles and turbulators may be the same or different. AA3xxx alloys for pipe cores are commonly referred to as "long life" alloys, in other words, they have good resistance to external brine corrosion.

Figure 2 shows a schematic diagram of a turbulator tube, designated as numeral 1, turbulator 3 and braze alloy cladding 2.

An example is given in application EP0283937a1 to Nihon Radiator co.ltd.

There are currently engine designs that reinject exhaust gas into the charge air cooler to mix it with clean air and return it to the intake, with the ultimate aim of reducing the pollutant emissions of the vehicle.

In this configuration, the off-gases that can condense can create a particularly severe corrosive environment in the cooler, characterized in particular by a low pH (which can be significantly lower than 3).

In the case of the prior art tube configurations described above, the silicon contained in the AA4xxx alloy of the cladding diffuses significantly to the core alloy forming the core of the tube during the brazing operation, thus degrading its corrosion resistance.

One solution known to those skilled in the art involves the insertion of an intermediate cladding made of AA1xxx or AA7xxx alloys between the tube core alloy and its internal coating made of AA4xxx braze alloy during the co-rolling process.

This configuration is schematically shown in fig. 3, the core being referred to as mark 3, the outer coating made of an AA4xxx alloy being referred to as mark 4, the inner coating also made of an AA4xxx alloy being referred to as mark 1, and the intermediate coating made of an AA1xxx or AA7xxx alloy being referred to as mark 2.

The coating acts by limiting the diffusion of silicon from the inner cladding to the core during brazing, thereby improving its corrosion resistance.

Sacrificial alloys common in the AA7xxx series are also used as the intermediate cladding alloy.

These "multi-coated" sheets are known to the person skilled in the art and are disclosed in particular in JP2003027166A of the application Kobe Steel ltd. Shinko Alcoa, JP2005224851A of Shinko AlcoaKizai KK, WO2006/044500a2 and WO2009/142651a2 of Alcoa Inc, WO2007/042206a1 of cornus alumium Walzprodukte GmbH, US2010/0159272a1 of novlis, etc.

The use of such "multi-clad" sheets in charge air coolers through which exhaust gases pass is disclosed in application WO2008/063855 to Modine Mfg co.

Applications EP1762810a1 and US2007/0051503a1 by Behr America inc. disclose another solution, including the formation of "brown bands" known to those skilled in the art, between the AA3xxx alloy core of the turbulator and its cladding consisting of an AA4xxx alloy (typically AA 4045) during a conventional type brazing process inside the tube. The tube is also typically made of an AA3xxx alloy having AA4xxx cladding on both sides thereof. In a highly preferred embodiment, the tube and the turbulator are made of substantially the same material.

However, although this configuration may slightly improve the corrosion resistance of the tubes, it is not sufficient under particularly severe load conditions, which is the case when the heat exchanger is subjected to exhaust gas recirculation, characterized in particular by a low pH.

Another solution consists of a surface treatment after brazing to improve the internal corrosion resistance of the tube. This is the case of the solution disclosed in application FR2916525a1 by Valeo Syst mes Thermiques, which recommends a resin-based coating. Another example of a surface treatment is given by application WO2010/019664, here an electro-ceramic deposition. Application FR2930023 by Valeo Syst mes Thermiques mentions the possibility of boehmite the whole exchanger. Finally, the solution disclosed in application EP1906131a2 to International transport comprises applying a Ni or Co based metal surface treatment on the inner surface of the tube and turbulators.

Finally, another solution is to use a combination of different materials, in particular aluminum and stainless steel. Application WO2008/095578 to behr gmbh & co, thus claims the use of stainless steel for turbulators, the tube being made of aluminum, whereas application EPI906127 to International Truck discloses an aluminum tube having a stainless steel coating on the inner surface, still having stainless steel turbulators.

However, these options are too expensive to provide an industrially satisfactory product.

Technical problem

The present invention aims to optimize the choice of materials made of aluminium alloy or brazing sheet for the preparation of heat exchanger tubes with brazed turbulators to increase the resistance in heavily corrosive environments, such as those resulting from automotive exhaust gas cycles, without increasing the number of materials used or the size or weight, the manufacturing conditions (ease of use and cost) starting from brazing sheet being at least equivalent to the solutions of the prior art.

Object of the Invention

The present invention is directed to an assembly of two brazing sheets, the first sheet consisting of AA3xxx alloy clad on one side with an AA1xxx alloy, and the second sheet consisting of AA3xxx aluminum alloy clad on both sides with an AA4xxx alloy, the two sheets being assembled with each other by brazing to form a closed channel or tube with internal turbulators inside which exhaust gases, especially from automobiles, pass alone or in combination with another fluid, usually air, the channel surface exposed to these gases or this mixture being the surface of the first sheet forming the channel coated with the 1xxx alloy, the second sheet forming the internal turbulators.

According to a preferred embodiment, the second brazing sheet consists of an aluminium alloy having the following composition (wt%):

0.3-1.0Fe <1.0Cu 0.3-1.0Mn 0.3-2.0Mg 0.3-3.0Zn <6.0Ti <0.1Zr <0.3Cr <0.3Ni <2.0Co <2.0Bi <0.5Y <0.5, other elements each <0.05 and the sum <0.15, the remainder being aluminum,

both surfaces of which are covered with an aluminium brazing alloy containing 4 to 15% silicon and 0.01 to 0.5% of at least one of the elements Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or misch metal, said two sheets being assembled to each other by fluxless brazing under a protective atmosphere.

According to an even more preferred embodiment, the second sheet forming the turbulator is constituted by an aluminium alloy having the following composition (wt%): 0.3-1.0Fe <0.5Cu 0.35-1.0Mn 1.0-2.0Mg 0.35-0.7Zn <0.2Ti <0.1Zr <0.3Cr <0.3Ni <1.0Co <1.0Bi <0.5Y <0.5, other elements each <0.05 and the sum <0.15, the remainder being aluminum,

both surfaces of which are covered with an aluminium brazing alloy containing 4 to 15% silicon and 0.01 to 0.5% of at least one of the elements Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or misch metal, said two sheets being assembled together by fluxless brazing under a protective atmosphere.

Furthermore, the first brazing sheet forming the channels or tubes may have fins or spacers on its outer surface, which fins or spacers themselves are made of an aluminium alloy core sheet having the following composition (in weight%):

0.3-1.0Fe <1.0Cu 0.3-1.0Mn 0.3-2.0Mg 0.3-3.0Zn <6.0Ti <0.1Zr <0.3Cr <0.3Ni <2.0Co <2.0Bi <0.5Y <0.5, other elements each <0.05 and the sum <0.15, the remainder being aluminum, both surfaces of which are covered with an aluminum brazing alloy containing 4 to 15% silicon and 0.01 to 0.5% of at least one element Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or misch elements, and assembled on the channel or tube by fluxless brazing under a protective atmosphere.

Preferably, the fins or spacers are made of a core sheet made of an aluminium alloy having the following composition (in wt%):

0.3-1.0Fe <0.5Cu 0.35-1.0Mn 1.0-2.0Mg 0.35-0.7Zn <0.2Ti <0.1Zr <0.3Cr <0.3Ni <1.0Co <1.0Bi <0.5Y <0.5, other elements each <0.05 and the sum <0.15, the remainder being aluminum, both surfaces of which are covered with an aluminum brazing alloy containing 4 to 15% silicon and 0.01 to 0.5% of at least one element Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or misch elements, and assembled on the channel or tube by fluxless brazing under a protective atmosphere.

According to another variant, the brazing sheet forming the channels or tubes is coated on the outer surface of said channels or tubes with a coating made of an AA4xxx alloy and fitted with fins or spacers on this coating, assembled by brazing.

Furthermore, the channels or tubes may be made of a core sheet made of an aluminium alloy having the following composition (wt%):

0.3-1.0Fe <1.0Cu 0.3-1.0Mn 0.3-2.0Mg 0.3-3.0Zn <6.0Ti <0.1Zr <0.3Cr <0.3Ni <2.0Co <2.0Bi <0.5Y <0.5, other elements each <0.05 and the sum <0.15, the remainder being aluminum, the outer surface of which is covered with an aluminum brazing alloy containing 4 to 15% silicon and 0.01 to 0.5% of at least one element Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or misch, and on which fins or spacers are assembled by fluxless brazing under a protective atmosphere.

Also preferably, the channels or tubes may be made of a core sheet made of an aluminium alloy having the following composition (wt%):

0.3-1.0Fe <0.5Cu 0.35-1.0Mn 1.0-2.0Mg 0.35-0.7Zn <0.2Ti <0.1Zr <0.3Cr <0.3Ni <1.0Co <1.0Bi <0.5Y <0.5, other elements each <0.05 and the sum <0.15, the remainder being aluminum, the outer surface of which is covered with an aluminum brazing alloy containing 4 to 15% silicon and 0.01 to 0.5% of at least one element Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or misch elements, and on which fins or spacers are assembled by fluxless brazing under a protective atmosphere.

Finally, these brazing sheets can be advantageously used in the composition of the turbulator tubes in heat exchangers, in particular of the type known under the term EGRC (Exhaust Gas Recirculation Cooler), in which only Exhaust gases from automobiles circulate; or EGR (exhaust gas Recirculation) circuit, of the type known under the term CAC (charge air cooler), inside which a mixture of fresh air and exhaust gases from the vehicle circulates.

The invention is also applicable to the type of heat exchanger tubes made of said brazing sheet, in which the exhaust gases, in particular car exhaust gases, are circulated alone or together with another fluid, usually air, and also to heat exchangers containing at least one such tube.

Drawings

Fig.1 shows a brazing sheet with three layers, the core sheet being labelled 2 and the brazing alloy (also called cladding) present on each face of the core being labelled 1.

Fig.2 schematically shows a tube 1 with turbulators 3, outside which fins or baffles (not shown) may be assembled to the outer surface of the tube by brazing. Similarly, the turbulators may be assembled to the inner surface of the tube by brazing. To achieve this, both surfaces of the tube are coated with a material known as a brazing material or a cladding material (typically AA4 xxx-series, labelled 2 in the figures).

Fig. 3 schematically illustrates a brazing sheet for the tube of fig.2, but with an intermediate cladding made of an AA1xxx or AA7xxx alloy interposed between the tube core alloy and its inner coating made of an AA4xxx brazing alloy.

The die portion is labeled 3, the exterior coating made of AA4xxx alloy is labeled 4, the interior coating made of AA4xxx alloy is labeled 1, and the middle coating made of AA1xxx or AA7xxx is labeled 2.

Figure 4 schematically shows a tube 1 with turbulators 4 of the present invention, which are themselves made of brazing sheet clad, and which tube 1 is also made of brazing sheet comprising a core sheet, typically made of AA3xxx alloy, with the inner surface of the tube coated with a clad 3 made of AA1xxx alloy and the outer surface coated with an AA4xxx brazing alloy layer 2, on which the uncoated fin is brazed.

Detailed Description

The invention comprises selecting the most suitable aluminium alloy forming the brazing sheet for the preparation of channels or tubes for heat exchangers with turbulators, more particularly for exchanger tubes with a severely corrosive environment, such as in particular tubes through which automotive recirculating exhaust gases pass.

Turbulators placed inside the tubes can be precisely designed to interfere with internal fluid circulation and improve heat exchange with external media.

At least within the scope of the present invention, the turbulators are generally composed of sheets arranged in a wavy manner along their length, similar to exchanger fins or baffles, which embodiments are well known to the person skilled in the art, as mentioned in the "prior art" section.

Still for factors considered within the scope of the invention, the tubes and turbulators are prepared by bending and assembling brazing sheet using common methods known to those skilled in the art.

The turbulators are assembled inside the tube by brazing. For this purpose, the brazing sheet forming the turbulator is made of a core sheet made of an AA3xxx alloy, coated on both surfaces with a cladding made of an AA4xxx brazing alloy.

The tube itself is composed of additional brazing sheet consisting of a core sheet made of an AA3xxx alloy, the invention including in particular forming the lining by cladding the inner surface of the tube, an AA1xxx alloy being chosen for this purpose.

According to the invention, the tube may have its outer surface coated with a coating made of an AA4xxx alloy to enable brazing of uncoated fins (also called separators) to this outer surface of the tube, or to enable brazing of the tube itself.

The different alloy clad-layers constituting the brazing sheet can usually be prepared by co-rolling, a commonly used method known to the person skilled in the art.

The applicant's published patent EP1687456B1 discloses a brazing sheet composition consisting of a core sheet made of an AA3xxx alloy coated on one or both surfaces with an AA4xxx brazing alloy, which can be subjected to a controlled atmosphere (also called protective atmosphere) (typically nitrogen and/or argon) in order to be usedThe method uses a standard furnace for flux-free brazing.

The brazing sheet consists of a core sheet made of an aluminium alloy having the following composition (wt%):

0.3-1.0Fe <1.0Cu 0.3-1.0Mn 0.3-2.0Mg 0.3-3.0Zn <6.0Ti <0.1Zr <0.3Cr <0.3Ni <2.0Co <2.0Bi <0.5Y <0.5, other elements each <0.05 and the sum <0.15, the remainder being aluminum,

at least one surface is covered with an aluminum brazing alloy containing 4 to 15% silicon and 0.01 to 0.5% of at least one element of Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or misch metals.

An even more preferred composition for the core alloy is as follows (in weight%): 0.3-1.0Fe <0.5Cu:0.35-1.0Mn:1.0-2.0Mg:0.35-0.7Zn <0.2Ti <0.1Zr <0.3Cr <0.3Ni <1.0Co <1.0Bi <0.5Y <0.5, other elements each <0.05 and the sum <0.15, the remainder being aluminum and the coating remaining unchanged.

According to two preferred embodiments of the invention, the first type of sheet and more advantageously the second type of sheet coated on both surfaces are chosen for the preparation of the turbulators, and can thus be assembled inside the tube by fluxless brazing under a protective atmosphere, thus resulting in a considerable cost reduction and preventing any risks related to possible entrainment of residual flux to the circulation.

Similarly, these two alloy compositions of the same coating configuration on both surfaces may be advantageously used for the preparation of fins or separators and their assembly achieved by flux-free brazing on the uncoated outer surface of the tube or channel, in other words directly brazed on the core AA3xxx alloy of the tube, in contact with the AA4xxx alloy of the fin according to the above-mentioned preferred composition.

Obviously, still according to the invention, it is also possible to coat the outside of the tubes or channels with a coating of an AA4xxx brazing alloy, so that standard fins or spacers, coated or uncoated, can be assembled by brazing.

Furthermore, the two types of sheet material with the above composition can be advantageously used for the production of the tubes or channels themselves, which are always coated on the inner surface with a coating made of an AA1xxx alloy and on the outer surface with an AA4xxx brazing alloy, said AA4xxxx enabling flux-free brazing of standard fins under a protective atmosphere.

It is evident that the invention is useful in particular for heat exchangers comprising such tubes, more particularly heat exchangers known to the person skilled in the art as EGRC (exhaust gas recirculation cooler), in which only exhaust gases from a motor vehicle are passed; or in EGR (exhaust gas recirculation) circuits of the type known as Charge Air Coolers (CAC), by means of a mixture of fresh air and vehicle exhaust gases, which in both cases is a particularly corrosive medium.

The details of the invention will be better understood on reading the following non-limiting examples.

Examples

Some sheets with 3916 core alloy and AA4045 braze alloy were cast while using AA1050 alloy sheets and sheets of each of alloys 3920 and 4945.

The 3916 alloy has the following composition (in weight%):

si 0.18Fe 0.15Cu 0.65Mn 1.35Ti 0.08 other elements are each <0.05 and the sum is <0.15, the remainder being aluminum,

the 3920 alloy has the following composition (in weight%):

si 0.5Fe 0.15Cu 0.5Mn 1.65Mg 0.5Ti 0.08 other elements each <0.05 and the sum <0.15, the remainder being aluminum,

4945 the alloy is AA4045 alloy which also contains 0.15% Bi.

The assembly from these sheets was carried out to obtain at the end of the transformation the coating percentages (total thickness%) shown in table 1 below.

These assemblies were hot and then cold rolled to produce 0.40mm thick clad strips for the tubes and 0.20mm thick clad strips for the turbulators. These strips were then subjected to a recovery treatment at 280 ℃ for 2 hours after a temperature increase at a rate of 45 ℃/h.

The tube model was fitted with turbulators and used for numbers 1 to 3 in Table 1Method brazing, using fluxless brazing for number 4, the temperature was increased at a rate of about 40 ℃/min up to 600 ℃, held at 600 ℃ for 2 minutes at constant temperature and then decreased at a rate of about 50 ℃/min, all at a nitrogen flow rate of 8 l/min.

The tested configurations are shown in table 1 below.

Configuration 1 is suitable for simple tubes made of 3916 core alloy coated on both sides with AA4045 braze alloy and turbulators made of AA3003 alloy.

Configuration 2 is identical except for an additional AA1050 alloy intermediate layer between the core and the AA4045 internal braze alloy.

Configuration 3 of the present invention uses a tube made of 3916 core alloy with AA4045 braze alloy coated on the outer surface and AA1050 braze alloy coated on the inner surface and a turbulator made of 3916 core alloy with AA4045 braze alloy coated on both sides.

The three cases of brazing using a fluxThe method is carried out.

Configuration 4 of the present invention uses a tube made of 3916 core alloy coated on the outside with AA4045 braze alloy and coated on the inside with AA1050 alloy and a turbulator made of an AA3920 core alloy coated on both faces with 4945 braze alloy (containing 0.15% Bi) according to the above preferred composition.

In this case, brazing is performed without flux under a protective atmosphere according to the above-mentioned patent filed by the applicant.

Table 1: configuration of model in corrosion test

The corrosion resistance of the tubes was tested by means of a corrosion test with alternate immersion and extraction in order to reproduce the conditions applied to a CAC (charge air cooler) type exchanger in an EGR (exhaust gas recirculation) low-pressure circuit. The detailed test conditions used are set forth in tables 2 and 3 below.

In practice, the test cycle consists of two repetitions of steps 1, 2 and 3 and three subsequent repetitions of steps 4, 5 and 6 and the complete cycle is repeated four thousand times.

Table 2: corrosion test parameters

Sulfate ion	Nitrate radical ion	Acetic acid	Formic acid	Propionic acid	Chloride ion	pH
							320	52	590	3167	474	20	2.5

Table 3: l1 composition (in ppm) for Corrosion testing

Sulfate ions are introduced in the form of sulfuric acid, nitrate ions are introduced in the form of acetic acid and chloride ions are introduced in the form of hydrochloric acid.

For each test configuration, corrosion resistance was evaluated by metallographic observation of the cross-section of the tube and turbulators.

The results obtained from the characterization of the samples after 300h are summarized in table 4 below.

Table 4: corrosion test characterization after 300h

The tubes of configurations 1 and 2 had severe corrosion that could lead to severe degradation of the perforations and some of the brazed joints between the tubes and the turbulators. The uncoated turbulators associated with this type of tube corroded only slightly.

On the other hand, configurations 3 and 4 of the present invention have very little pipe corrosion, typically limited to cladding. Corrosion of the brazed joint is also limited. The turbulators associated with this type of tube corrode severely. However, this situation is considered significantly better.

A single perforation of the tube causes leakage throughout the heat exchanger cycle. The leakage of the turbulators causes a reduction in the heat exchange quality of the exchanger.

It is therefore easy to understand that maintaining the integrity of the tube is more important than the integrity of the turbulators.

The claims (modification according to treaty clause 19)

1. An assembly of two brazing sheets characterized by:

-the first sheet consists of an AA3xxx alloy having a coating of an AA1xxx alloy on one side,

-the second sheet consists of an AA3xxx aluminum alloy having a coating of an AA4xxx alloy on both sides,

the two sheets are assembled to each other by brazing to form a closed channel or tube with internal turbulators inside which the exhaust gases, in particular from the automobile, pass alone or in combination with another fluid, usually air,

the channel surface exposed to the gases or the mixture is the surface of the first sheet forming the channel coated with the 1xxx alloy, the second sheet forming the internal turbulator.

2. An assembly of two brazing sheets according to claim 1, characterized in that the second brazing sheet consists of an aluminium alloy having the following composition (in weight%):

0.3-1.0Fe <1.0Cu 0.3-1.0Mn 0.3-2.0Mg 0.3-3.0Zn <6.0Ti <0.1Zr <0.3Cr <0.3Ni <2.0Co <2.0Bi <0.5Y <0.5, other elements each <0.05 and the sum <0.15, the remainder being aluminum,

both surfaces of which are covered with an aluminum brazing alloy containing 4 to 15% silicon and 0.01 to 0.5% of at least one element of Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or misch metal,

the two sheets are assembled to each other by fluxless brazing under a protective atmosphere.

3. An assembly of two brazing sheets according to claim 2, characterized in that the second sheet consists of an aluminium alloy having the following composition (in weight%):

0.3-1.0Fe <0.5Cu 0.35-1.0Mn 1.0-2.0Mg 0.35-0.7Zn <0.2Ti <0.1Zr <0.3Cr <0.3Ni <1.0Co <1.0Bi <0.5Y <0.5, other elements each <0.05 and the sum <0.15, the remainder being aluminum,

both surfaces of which are covered with an aluminum brazing alloy containing 4 to 15% silicon and 0.01 to 0.5% of at least one element of Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or misch metal,

the two sheets are assembled together by fluxless brazing under a protective atmosphere.

4. Assembly of two brazing sheets according to any one of claims 1 to 3, characterized in that it has fins or spacers on the outer surface of the first sheet forming the channels, which fins or spacers are themselves made of an aluminium alloy core sheet having the following composition (in weight%):

0.3-1.0Fe <1.0Cu 0.3-1.0Mn 0.3-2.0Mg 0.3-3.0Zn <6.0Ti <0.1Zr <0.3Cr <0.3Ni <2.0Co <2.0Bi <0.5Y <0.5, other elements each <0.05 and the sum <0.15, the remainder being aluminum, both surfaces of which are covered with an aluminum brazing alloy containing 4 to 15% silicon and 0.01 to 0.5% of at least one element Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or misch elements, and assembled on the channel by fluxless brazing under a protective atmosphere.

5. Assembly of two brazing sheets according to any one of claims 1 to 4, characterized in that it has fins or spacers on the outer surface of the first sheet forming the channels, which fins or spacers are themselves made of an aluminium alloy core sheet having the following composition (in weight%):

0.3-1.0Fe <0.5Cu 0.35-1.0Mn 1.0-2.0Mg 0.35-0.7Zn <0.2Ti <0.1Zr <0.3Cr <0.3Ni <1.0Co <1.0Bi <0.5Y <0.5, other elements each <0.05 and the sum <0.15, the remainder being aluminum, both surfaces of which are covered with an aluminum brazing alloy containing 4 to 15% silicon and 0.01 to 0.5% of at least one element Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or misch elements, and assembled on the channel by fluxless brazing under a protective atmosphere.

6. Assembly of two brazing sheets according to any one of claims 1 to 3, characterized in that the channels are coated on the outer surface with a coating made of AA4 xxx-alloy and on this coating are fitted fins or spacers, assembled by brazing.

7. An assembly of two brazing sheets according to any one of claims 1 to 3, characterized in that the channels are made of a core sheet made of an aluminium alloy having the following composition (in weight%):

0.3-1.0Fe <1.0Cu 0.3-1.0Mn 0.3-2.0Mg 0.3-3.0Zn <6.0Ti <0.1Zr <0.3Cr <0.3Ni <2.0Co <2.0Bi <0.5Y <0.5, other elements each <0.05 and the sum <0.15, the remainder being aluminum,

the outer surface of which is covered with an aluminum brazing alloy containing 4 to 15% silicon and 0.01 to 0.5% of at least one element of Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or misch metal, and on which layer fins or spacers are assembled by fluxless brazing under a protective atmosphere.

8. An assembly of two brazing sheets according to any one of claims 1 to 3, characterized in that the channels are made of a core sheet made of an aluminium alloy having the following composition (in weight%):

0.3-1.0Fe <0.5Cu 0.35-1.0Mn 1.0-2.0Mg 0.35-0.7Zn <0.2Ti <0.1Zr <0.3Cr <0.3Ni <1.0Co <1.0Bi <0.5Y <0.5, other elements each <0.05 and the sum <0.15, the remainder being aluminum,

the outer surface of which is covered with an aluminum brazing alloy containing 4 to 15% silicon and 0.01 to 0.5% of at least one element of Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or misch metal, and on which layer fins or spacers are assembled by fluxless brazing under a protective atmosphere.

9. An assembly of two brazing sheets according to any one of claims 1 to 8, characterized in that it constitutes a component of a heat exchanger.

10. An assembly of two brazing sheets according to claim 9, characterized in that it constitutes a component of a heat exchanger, termed by the term EGRC (exhaust gas recirculation cooler), in which only exhaust gases from a motor vehicle are circulated.

11. An assembly of two brazing sheets according to claim 9, characterized in that it constitutes a component of a heat exchanger in an EGR (exhaust gas recirculation) circuit, termed by the term CAC (charge air cooler), inside which a mixture of fresh air and exhaust gases from a car is circulated.

12. Heat exchanger tube made of a brazing sheet according to any one of claims 1 to 8, inside which exhaust gases, in particular automotive exhaust gases, are circulated alone or together with another fluid, usually air.

13. Heat exchanger, characterized in that it comprises at least one tube according to claim 12.

Claims (13)

1. An assembly of two brazing sheets characterized by:

-the first sheet consists of an AA3xxx alloy having a coating of an AA1xxx alloy on one side,

-the second sheet consists of an AA3xxx aluminum alloy having a coating of an AA4xxx alloy on both sides,

the two sheets are assembled to each other by brazing to form a closed channel or tube with internal turbulators inside which the exhaust gases, in particular from the automobile, pass alone or in combination with another fluid, usually air,

the channel surface exposed to the gases or the mixture is the surface of the first sheet forming the channel coated with the 1xxx alloy, the second sheet forming the internal turbulator.

2. An assembly of two brazing sheets according to claim 1, characterized in that the second brazing sheet consists of an aluminium alloy having the following composition (in weight%):

0.3-1.0Fe <1.0Cu 0.3-1.0Mn 0.3-2.0Mg 0.3-3.0Zn <6.0Ti <0.1Zr <0.3Cr <0.3Ni <2.0Co <2.0Bi <0.5Y <0.5, other elements each <0.05 and the sum <0.15, the remainder being aluminum,

both surfaces of which are covered with an aluminum brazing alloy containing 4 to 15% silicon and 0.01 to 0.5% of at least one element of Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or misch metal,

the two sheets are assembled to each other by fluxless brazing under a protective atmosphere.

3. An assembly of two brazing sheets according to claim 2, characterized in that the second sheet consists of an aluminium alloy having the following composition (in weight%):

0.3-1.0Fe <0.5Cu 0.35-1.0Mn 1.0-2.0Mg 0.35-0.7Zn <0.2Ti <0.1Zr <0.3Cr <0.3Ni <1.0Co <1.0Bi <0.5Y <0.5, other elements each <0.05 and the sum <0.15, the remainder being aluminum,

both surfaces of which are covered with an aluminum brazing alloy containing 4 to 15% silicon and 0.01 to 0.5% of at least one element of Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or misch metal,

the two sheets are assembled together by fluxless brazing under a protective atmosphere.

4. Assembly of two brazing sheets according to any one of claims 1 to 3, characterized in that it has fins or spacers on the outer surface of the first sheet forming the channels, which fins or spacers are themselves made of an aluminium alloy core sheet having the following composition (in weight%):

0.3-1.0Fe <1.0Cu 0.3-1.0Mn 0.3-2.0Mg 0.3-3.0Zn <6.0Ti <0.1Zr <0.3Cr <0.3Ni <2.0Co <2.0Bi <0.5Y <0.5, other elements each <0.05 and the sum <0.15, the remainder being aluminum, both surfaces of which are covered with an aluminum brazing alloy containing 4 to 15% silicon and 0.01 to 0.5% of at least one element Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or misch elements, and assembled on the channel by fluxless brazing under a protective atmosphere.

5. Assembly of two brazing sheets according to any one of claims 1 to 4, characterized in that it has fins or spacers on the outer surface of the first sheet forming the channels, which fins or spacers are themselves made of an aluminium alloy core sheet having the following composition (in weight%):

0.3-1.0Fe <0.5Cu 0.35-1.0Mn 1.0-2.0Mg 0.35-0.7Zn <0.2Ti <0.1Zr <0.3Cr <0.3Ni <1.0Co <1.0Bi <0.5Y <0.5, other elements each <0.05 and the sum <0.15, the remainder being aluminum, both surfaces of which are covered with an aluminum brazing alloy containing 4 to 15% silicon and 0.01 to 0.5% of at least one element Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or misch-metals, without flux brazing under a protective atmosphere.

6. Assembly of two brazing sheets according to any one of claims 1 to 3, characterized in that the channels are coated on the outer surface with a coating made of AA4 xxx-alloy and on this coating are fitted fins or spacers, assembled by brazing.

7. An assembly of two brazing sheets according to any one of claims 1 to 3, characterized in that the channels are made of a core sheet made of an aluminium alloy having the following composition (in weight%):

0.3-1.0Fe <1.0Cu 0.3-1.0Mn 0.3-2.0Mg 0.3-3.0Zn <6.0Ti <0.1Zr <0.3Cr <0.3Ni <2.0Co <2.0Bi <0.5Y <0.5, other elements each <0.05 and the sum <0.15, the remainder being aluminum,

the outer surface of which is covered with an aluminum brazing alloy containing 4 to 15% silicon and 0.01 to 0.5% of at least one element of Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or misch metal, and on which layer fins or spacers are assembled by fluxless brazing under a protective atmosphere.

8. An assembly of two brazing sheets according to any one of claims 1 to 3, characterized in that the channels are made of a core sheet made of an aluminium alloy having the following composition (in weight%):

0.3-1.0Fe <0.5Cu 0.35-1.0Mn 1.0-2.0Mg 0.35-0.7Zn <0.2Ti <0.1Zr <0.3Cr <0.3Ni <1.0Co <1.0Bi <0.5Y <0.5, other elements each <0.05 and the sum <0.15, the remainder being aluminum,

the outer surface of which is covered with an aluminum brazing alloy containing 4 to 15% silicon and 0.01 to 0.5% of at least one element of Ag, Be, Bi, Ce, La, Pb, Pd, Sb, Y or misch metal, and on which layer fins or spacers are assembled by fluxless brazing under a protective atmosphere.

9. An assembly of two brazing sheets according to any one of claims 1 to 8, characterized in that it constitutes a component of a heat exchanger.

10. An assembly of two brazing sheets according to claim 9, characterized in that it constitutes a component of a heat exchanger, termed by the term EGRC (exhaust gas recirculation cooler), in which only exhaust gases from a motor vehicle are circulated.

11. An assembly of two brazing sheets according to claim 9, characterized in that it constitutes a component of a heat exchanger in an EGR (exhaust gas recirculation) circuit, termed by the term CAC (charge air cooler), inside which a mixture of fresh air and exhaust gases from a car is circulated.

12. Heat exchanger tube made of a brazing sheet according to any one of claims 1 to 8, inside which exhaust gases, in particular automotive exhaust gases, are circulated alone or together with another fluid, usually air.

13. Heat exchanger, characterized in that it comprises at least one tube according to claim 12.