EP3934908A1

EP3934908A1 - Strip of aluminum alloy for manufacturing brazed heat exchangers

Info

Publication number: EP3934908A1
Application number: EP20719682.5A
Authority: EP
Inventors: Lionel PEGUET; Bechir CHEHAB
Original assignee: Constellium Neuf Brisach SAS
Current assignee: Constellium Neuf Brisach SAS
Priority date: 2019-03-04
Filing date: 2020-02-27
Publication date: 2022-01-12
Also published as: DE20719682T1; JP2022522881A; US11932922B2; FR3093451A1; FR3093450A1; KR20210135271A; US20220145432A1; FR3093451B1

Abstract

The invention relates to a strip intended for use in the manufacture of brazed heat exchangers, comprising a core made of an alloy with the following composition (in mass %): Si: 0.10 – 0.30%, preferably 0.15 – 0.25%; Fe: < 0.20%; Cu: 0.75 – 1.05%, preferably 0.75 – 1.02%, more preferably 0.75 – 1.0%; Mn: 1.2 – 1.7 %, preferably 1.2 – 1.55 %, more preferably 1.25 –1.4 %; Mg: < 0.03%, preferably < 0.025%, more preferably < 0.015%; Zn: < 0.1%; Ti: < 0.15%; other elements: < 0.05% each and < 0.15% in total; remainder aluminium.

Description

DESCRIPTION

Title: Aluminum alloy strip for the manufacture of brazed heat exchangers

Field of the invention

The invention relates to thin strips (of thickness generally between 0.05 to 3 mm, preferably 0.15 to 2.5 mm) of aluminum-manganese core alloy (3000 series according to the nomenclature of the Aluminum Association), optionally plated on one or both sides of a cover alloy, most often an aluminum-silicon brazing alloy (4000 series according to the Aluminum Association nomenclature) and / or an intermediate alloy, placed between the core and the possible brazing alloy, in aluminum-manganese alloy (3000 series according to the Aluminum Association nomenclature). These bands are intended in particular for the manufacture of elements, such as tubes, collectors and plates, of 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 "The strong brazing of aluminum and its alloys", published in Soudage et Techniques Connexes, Nov.- Dec. 1991, pp. 18-29. The strips according to the invention can be used in brazing techniques with non-corrosive flux of NOCOLOK ^® kind or CAB (controlled atmosphere brazing), or, alternatively, in brazing techniques without flux.

State of the art

The properties required for the aluminum alloy strips used for the manufacture of brazed exchangers are in particular good brazability, high mechanical strength after brazing, so as to use thicknesses as low as possible, formability sufficient for easy shaping of tubes, manifold fins and plates, before brazing, and good corrosion resistance. Of course, it is important that the alloy chosen is easy to cast and roll, and that the cost of manufacturing the strips is compatible with the requirements of the automotive industry.

An alloy used is 3003 with the composition (% by weight according to standard EN 573-3):

Si <0.6% Fe <0.7% Cu: 0.05 - 0.20% Mn: 1.0 - 1.5% Zn <0.10% other elements <0.05% each and <0, 15% in total, aluminum balance. Numerous alloys have been proposed to improve one or the other of the use properties mentioned above, more particularly the resistance to corrosion, hence the name of “long-life” alloys which is sometimes given to them. in the profession.

US Patent 5,125,452 (Sumitomo Light Métal Industries and Nippondenso) describes plated bands whose base alloy has the following composition:

Si <0.1 Fe <0.3 Cu: 0.05 - 0.35 Mn: 0.3 - 1.5 Mg: 0.05 - 0.5

Ti: 0.05 - 0.35 with Cu - 0.2 <Mg <Cu + 0.2.

Patent EP 0326337 (Alcan International) describes a plated strip whose base alloy has the composition:

Si <0.15 Fe <0.4 Cu: 0.1 - 0.6 Mn: 0.7 - 1.5 Mg <0.8.

The low Si content, preferably <0.05%, allows the formation of a dense layer of Mn precipitates, which can act as a barrier to the diffusion of the silicon of the coating alloy, and increases the strength. corrosion. WO 94/22633 is a variant of the previous one which differs only by a higher Cu content (0.6 - 0.9%).

US Patent 5,350,436 (Kobe Alcoa and Nippondenso) describes a base alloy of composition: Si: 0.3 - 1.3 Cu <0.2 Mn: 0.3 - 1.5 Mg <0.2 Ti: 0, 02 - 0.3 Fe not mentioned.

Without being bound by theory, it would seem that the high Si content (0.8% in the examples) makes it possible to compensate for the absence of Cu and Mg for mechanical strength, the presence of Ti contributes to good resistance to corrosion. corrosion and the absence of Mg promotes good solderability.

Patent EP 0718072 (Hoogovens Aluminum Walzprodukte) describes a base alloy of composition: Si> 0.15 Fe <0.8 Cu: 0.2 - 2 Mn: 0.7 - 1.5 Mg: 0.1 - 0 , 6 with

Cu + Mg <0.7 and possible addition of Ti, Cr, Zr or V. The examples show Si contents of 0.5%.

JP 2000167688 (Sumitomo Light Métal Ind) discloses an aluminum core alloy comprising, in weight percentages, from 0.5 to 2.0% Mn, 0.1 to 1.0% Cu, <= 0.1% Si, <= 0.3% Fe, 0.06-0.35% Ti, <= 0.04% Mg and unavoidable impurities, the rest being aluminum.

If we want to summarize the teaching of the state of the art for this type of alloy, we see that a first category of alloys has a very low Si content (<0.15 and preferably <0.05 %) with or without a low Fe content, but, in all cases, less demanding than for Si. These very low Si contents (<0.05%) can only be obtained starting from bases pure, which increases manufacturing costs. A second category of alloys, by questioning the need for a very low Si content to obtain good corrosion resistance, on the contrary has a rather high Si content (0.5 to 0.8%), possibly for compensate for the loss of mechanical strength linked to low contents of Mg and Cu hardening elements. In fact, for soldering with flux, it is known that the Mg content must be reduced, in order to limit the migration of Mg to the surface of the cladding layer, which leads to the formation of a thick layer of MgO oxide. . The presence of this oxide makes it necessary to increase the quantity of flux on the surfaces to be brazed, which increases the cost of the assembly and deteriorates the surface appearance. Still other references relate to an intermediate Si content (see for example EP1075935, EP1413427, EP2969308, or else US 9,546,829).

As for the element Cu, its influence on corrosion resistance seems controversial. Certain references encourage not to use an excessively high quantity of Cu (see in particular US patent 6,019,939 to Alcan International Limited).

In the face of increasing market demand, there remains a need for a new core alloy having improved corrosion resistance over existing alloys, without degradation in strength or solderability. Such a core alloy could make it possible to meet the ever-present demand for reducing the thickness of the products.

Object of the invention

Surprisingly, the Applicant has determined a range of composition making it possible to improve corrosion resistance without degrading mechanical strength or solderability.

The subject of the invention is thus a strip, intended for the manufacture of brazed heat exchangers, having an aluminum alloy core of composition (% by mass):

Si: 0.10 - 0.30%, preferably 0.15 - 0.25%

Fe <0.20%

Cu: 0.75 - 1.05%, preferably 0.75 - 1.02%, more preferably 0.75-1.0%

Mn: 1.2 - 1.7%, preferably 1.2 - 1.55%, more preferably 1.25 - 1.4%

Mg <0.03% preferably <0.025%, more preferably <0.015%

Zn <0.1%

Ti <0.15%

other elements <0.05% each and <0.15% in total,

remains aluminum. The subject of the invention is also a method of manufacturing a strip, comprising the successive steps of:

- casting of a core alloy plate;

- optional plating with at least one brazing aluminum alloy and optionally at least one intermediate aluminum alloy;

- preheating to a temperature of 450 to 520 ° C, preferably with a maintenance at the maximum temperature for less than 12 hours, more preferably for less than 3 hours;

- hot rolling of this plate without prior homogenization at a temperature of 450 to 520 ° C to a thickness of 2 to 6 mm,

- cold rolling to the desired thickness, the thickness of the strip after cold rolling preferably being 0.15 to 3 mm and

- annealing at a temperature of 240 to 450 ° C, preferably 240 to 380 ° C, with maintenance at the maximum temperature for 10 minutes to 15 hours, preferably for 20 minutes to 3 hours.

According to one variant, the subject of the invention is also a method for manufacturing a strip according to the present invention, comprising the successive steps of:

- casting of a core alloy plate,

- homogenization of this plate between 580 and 630 ° C for 1 to 24 hours;

- hot rolling of the homogenized and possibly plated plate at a - - temperature of 450 to 520 ° C up to a thickness of 2 to 6 mm;

The subject of the invention is also a heat exchanger produced at least in part from a strip according to the present invention. A subject of the invention is also the use of a strip according to the present invention, for the manufacture of a heat exchanger, said strip exhibiting improved corrosion resistance without degradation of the mechanical resistance or of the solderability.

Description of figures

[Fig. 1] FIG. 1 represents the sectional micrographs of the bands after SWAAT test (ASTM G85A3) for the samples of Example 1, after four weeks of exposure. The deepest corrosion sites are shown. The mark A corresponds to the sample having a core alloy A (prior art). The mark B corresponds to the sample having a core alloy B (according to the invention). The mark C corresponds to the sample having a core C alloy (according to the invention).

[Fig. 2] FIG. 2 represents the sectional micrographs of the bands after SWAAT test for the samples of Example 2, after two weeks of exposure. The E mark corresponds to the sample having an E core alloy (according to the invention). The mark F corresponds to the sample having a core alloy F (prior art).

Description of the invention

In the description and the claims, unless otherwise indicated:

the designation of aluminum alloys conforms to the nomenclature of The Aluminum Association;

the contents of chemical elements are designated as percentages by mass.

The strip according to the present invention comprises an aluminum alloy core of composition (% by mass):

Si: 0.10 - 0.30%, preferably 0.15 - 0.25%

Fe <0.20%

Cu: 0.75 - 1.05%, preferably 0.75 - 1.02%, more preferably 0.75-1.0%

Mn: 1.2 - 1.7%, preferably 1.2 - 1.55%, more preferably 1.25 - 1.4%

Mg <0.03% preferably <0.025%, more preferably <0.015%

Zn <0.1%

Ti <0.15%

other elements <0.05% each and <0.15% in total,

remains aluminum.

The compositional limits of the core alloy can be justified as follows. A minimum silicon content of 0.10% makes it possible to avoid using a pure base, the cost of which is high. Furthermore, in alloys containing magnesium, silicon contributes to the mechanical strength by forming Mg2Si precipitates. Beyond 0.30%, silicon can have an unfavorable influence on corrosion resistance, due to the formation of manganese dispersoids AIMnSi and AIMnFeSi.

An iron content limited to less than 0.25% is also favorable to corrosion resistance and formability, but it is not necessary to go down to very low contents <0.15% which would lead to prices high cost.

Copper is a hardening element which contributes to the mechanical resistance, but above 1.1%, coarse intermetallic compounds are formed on casting which adversely affect the homogeneity of the metal and constitute sites of initiation of the metal. corrosion.

The manganese is within limits close to those of the alloy 3003; it contributes to mechanical strength and corrosion resistance.

A limited addition of zinc can have a beneficial effect on corrosion resistance, by modifying the electrochemical mechanisms, especially for the alloys with the highest copper content. However, it must remain below 0.2% to avoid too high a susceptibility to generalized corrosion.

Preferably, the core alloy comprises less than 0.1% Ti. Preferably, the core alloy comprises at least 0.05%, more preferably at least 0.06% Ti.

Aluminum alloy brazing

The strips according to the present invention have a thickness generally comprised from 0.05 to 3 mm, preferably 0.15 to 2.5 mm, depending on the type of part manufactured, and can be plated with a cover 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 a zinc alloy such as the AA7072 alloy.

According to a variant of the present invention, the brazing aluminum alloy does not include a deliberate addition of Zn, the Zn then preferably being present in an amount corresponding to the impurities, ie less than 0.05% by mass.

The brazing alloy is of the 4xxx family of alloys with a liquidus temperature sufficiently low compared to the solidus of the core alloy to have a sufficient temperature range for brazing, acceptable mechanical strength and good wettability. These alloys can contain addition elements, for example strontium.

Preferably, the strip according to the present invention is plated on one or both sides of a brazing aluminum alloy, preferably a 4xxx alloy comprising from 4 to 13%, preferably from 6 to 11% by mass of Si and up to 0.5%, preferably up to 0.3% by mass of Fe. Preferably, the brazing aluminum alloy comprises (% by mass):

Si: from 5 to 13%;

Fe: up to 1%;

Cu: up to 0.4%, preferably up to 0.1%;

Mn: up to 0.2%, preferably up to 0.1%;

Mg: up to 0.3%, preferably up to 0.1%;

Zn: up to 0.2%, preferably up to 0.1%;

Ti: up to 0.30%, preferably up to 0.1%;

other items: less than 0.05% each and less than 0.15% in total;

remains aluminum.

By way of example, composition AA4045 is an aluminum alloy which may be suitable as a brazing alloy according to the present invention. Its composition is, in% by mass: from 9 to 11% of Si, up to 0.8% of Fe, up to 0.30% of Cu, up to 0.05% of Mn, up to 0.05% Mg, up to 0.10% Zn, up to 0.20% Ti, other elements less than 0.05% each and less than 0.15% in total, the remainder being aluminum.

By way of example, the preceding composition preferably comprises up to 0.6% Fe.

By way of example, the preceding composition preferably comprises up to 0.1% Cu.

By way of example, composition AA4343 is an aluminum alloy which may be suitable as a brazing alloy according to the present invention. Its composition is, in% by mass: from 6.8 to 8.2% of Si, up to 0.8% of Fe, up to 0.25% of Cu, up to 0.10% of Mn , up to 0.05% Mg, other elements less than 0.05% each and less than 0.15% in total, the remainder being aluminum.

By way of example, the preceding composition preferably comprises up to 0.3% of Fe. By way of example, the preceding composition preferably comprises up to 0.1% of Cu. Preferably, the brazing alloy according to the present invention does not include Mg.

It is also possible to use as plating, on one of the faces, an aluminum alloy with a sacrificial anode effect, in particular an alloy containing zinc, such as the AA7072 alloy. Aluminum alloy interlayer

Preferably, the strip according to the present invention is plated on one or two faces of a so-called interlayer aluminum alloy, placed between the core and the possible brazing alloy, preferably comprising (in% by mass):

Si: up to 0.5%, more preferably up to 0.2%;

Fe: up to 0.7%, more preferably up to 0.3%, even more preferably up to 0.2%;

Mn: from 0.3 to 1.4%, more preferably from 0.6 to 0.8%, according to a variant between 1 and 1.3%;

Cu: up to 0.3%, preferably up to 0.1%, even more preferably up to 0.05%;

other elements <0.05% each and <0.15% in total;

remains aluminum.

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

Preferably, the intermediate aluminum alloy is an AA3xxx series alloy.

Bandaged

The strip according to the present invention is a so-called brazing strip, which can be used for the manufacture of different parts of a heat exchanger, for example tubes, plates, collectors, etc.

Process

The subject of the invention is also a method of manufacturing a strip, comprising the successive steps of:

- casting of a core alloy plate;

- hot rolling without prior homogenization at a temperature of 450 to 520 ° C up to a thickness of 2 to 6 mm;

- casting of a core alloy plate; - homogenization of this plate at a temperature of 580 to 630 ° C for 1 to 24 hours;

- hot rolling of the homogenized and possibly plated plate, at a temperature of 450 to 520 ° C to a thickness of 2 to 6 mm;

Preferably, there is no intermediate annealing in the processes according to the present invention.

When intended for parts with significant shaping, the strip can be used in the annealed state (O state) by carrying out a final annealing at a temperature between 320 and 380 ° C, in a continuous furnace or in batch oven. This annealing leads to the recrystallization of the alloy and improves the formability. In other cases, it is used in the hardened state, which leads to better mechanical resistance, for example an H14 or H24 state (according to standard NF EN 515), the latter state being obtained by a restoration annealing between 250 and 300 ° C, avoiding recrystallization

Prior to installing the plating material, the core alloy plate can be homogenized at a temperature of 580 to 630 ° C. This homogenization is favorable to the ductility of the rolled strip and it is recommended when the strip is used in the O state. It promotes the coalescence of the dispersoids with Mn.

use

The subject of the invention is also a heat exchanger produced at least in part from a strip according to the present invention.

A subject of the invention is also the use of a strip according to the present invention, for the manufacture of a heat exchanger, said strip exhibiting improved corrosion resistance without degradation of the mechanical resistance or of the solderability. The tapes 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 charge air coolers, as well as in air conditioning systems.

Examples

Example 1

Four alloys were cast, the compositions of which are given in Table 1 below in percentages by weight. Alloy A is a core alloy according to the prior art. Alloys B and C are core alloys according to the present invention. Alloy D is AA4343 brazing alloy.

[Table 1]

The alloys described in Table 1 above were used to form three-layer sandwiches having a total thickness of 220 µm, according to the following configuration:

brazing alloy (alloy D - 10% of total thickness)

core alloy (alloy A, B or C - 80% of total thickness)

brazing alloy (alloy D - 10% of total thickness).

After casting and assembling the layers, the sandwiches were preheated to 500 ° C. and hot rolled at this temperature to a total thickness of 3.5 mm. Then the sandwiches were cold rolled without intermediate annealing to a total thickness of 220 µm. Finally, the bands obtained were subjected to a restoration annealing to obtain a metallurgical state H24, at 240 ° C. for 2 hours.

Brazing was then carried out in a Camlaw oven for 2 minutes at 600 ° C.

On the sandwiches thus obtained, the puncture depth was determined using the SWAAT test (sea water acetic acid test) according to the ASTM G85A3 standard, followed by micrographic observation under an optical microscope (magnification x100) after four weeks of 'exposure. The results are shown in Figure 1.

FIG. 1 shows that the core alloys according to the present invention make it possible to improve the corrosion resistance compared to the core alloy according to the prior art. On the other hand, the mechanical strengths after brazing of the alloys A, B and C described in Table 1 above were measured according to the ISO 6892-1 standard. The results obtained are presented in Table 2 below.

[Table 2]

According to Table 2 above, the core alloy according to the present invention exhibits mechanical strengths of the same order of magnitude, or even improved, compared to the core alloy of the prior art.

Example 2

Three alloys were cast, the compositions of which are given in Table 3 below in percentages by weight. Alloy E is a core alloy according to the present invention. Alloy F is a core alloy according to the prior art. Alloy D is AA4343 brazing alloy.

[Table 3]

The alloys described in Table 3 above were used to form three-layer sandwiches having a total thickness of 400 µm, according to the following configuration:

brazing alloy (alloy D - 7.5% of total thickness)

core alloy (alloy E or F - 85% of total thickness)

brazing alloy (alloy D - 7.5% of total thickness).

After casting, homogenization and assembly of the layers, the sandwiches were preheated to 500 ° C and hot rolled at this temperature to a total thickness of 3.5 mm. Then the sandwiches were cold rolled without intermediate annealing to a total thickness of 400 µm. Finally, the strips obtained were subjected to annealing to obtain a metallurgical state 0 at 360 ° C. for 1 hour.

Brazing was then carried out in a Camlaw oven for 2 minutes at 600 ° C.

On the sandwiches thus obtained, the puncture depth was determined using the SWAAT test (sea water acetic acid test) according to the ASTM G85A3 standard, followed by an observation micrographic under optical microscope (magnification x100) after two weeks of exposure. The results are shown in Figure 2.

FIG. 2 shows that the core alloy according to the present invention (comprising in particular Cu from 0.75 to 1.05%) makes it possible to improve the corrosion resistance compared with the core alloy according to the prior art.

Claims

1. Strip, intended for the manufacture of brazed heat exchangers, having an aluminum alloy core of composition (% by mass):

Si: 0.10 - 0.30%, preferably 0.15 - 0.25%

Fe <0.20%

Cu: 0.75 - 1.05%, preferably 0.75 - 1.02%, more preferably 0.75-1.0%

Mn: 1.2 - 1.7%, preferably 1.2 - 1.55%, more preferably 1.25 - 1.4% Mg <0.03% preferably <0.025%, more preferably <0.015%

Zn <0.1%

Ti <0.15%

other elements <0.05% each and <0.15% in total,

remains aluminum.

2. Strip according to claim 1, characterized in that it is plated on one or both sides of a brazing aluminum alloy, preferably a 4xxx alloy comprising from 4 to 13%, preferably from 6 to 11% by mass of Si and up to 0.5%, preferably up to 0.3% by mass of Fe.

3. Strip according to claim 2, characterized in that the brazing aluminum alloy comprises (% by mass):

Si: from 5 to 13%;

Fe: up to 1%;

Cu: up to 0.4%;

Mn: up to 0.2%;

Mg: up to 0.3%;

Zn: up to 0.2%;

Ti: up to 0.30%;

other items: less than 0.05% each and less than 0.15% in total;

remains aluminum.

4. Strip according to any one of claims 1 to 3, characterized in that it is plated on one or both sides of an aluminum alloy called interlayer, placed between the core and the possible brazing alloy, preferably comprising (in% by mass):

Si: up to 0.5%, more preferably up to 0.2%;

Fe: up to 0.7%, more preferably up to 0.3%, even more

preferably up to 0.2%;

Cu: up to 0.3%, preferably up to 0.1%, even more preferably up to 0.05%;

other elements <0.05% each and <0.15% in total;

remains aluminum.

5. Strip according to claim 4, characterized in that the aluminum alloy

interlayer comprises (% by mass): Si <0.15%; Fe <0.2%; Cu <0.1%; Mn from 0.6 to 0.8%; Mg <0.02%; other elements <0.04% and <0.15% in total, remainder aluminum.

6. A method of manufacturing a strip according to any one of claims 1 to 5, comprising the successive steps of:

- casting of a core alloy plate;

- hot rolling of this plate without prior homogenization at a - temperature of 450 to 520 ° C to a thickness of 2 to 6 mm;

- annealing at a temperature of 240 to 450 ° C, with maintenance at the maximum temperature for 10 minutes to 15 hours.

7. A method of manufacturing a strip according to any one of claims 1 to 5, comprising the successive steps of:

- casting of a core alloy plate;

- homogenization of this plate at a temperature of 580 to 630 ° C for 1 to 24 hours;

- hot rolling of the homogenized and optionally plated plate at a temperature of 450 to 520 ° C to a thickness of 2 to 6 mm;

8. Heat exchanger produced at least in part from a strip according to any one of claims 1 to 5.

9. Use of a strip according to any one of claims 1 to 5, for the manufacture of a heat exchanger, said strip having improved corrosion resistance without degradation of mechanical strength or solderability.