Multi-layer brazing sheet

Abstract

To provide a multilayer brazing sheet made of an aluminium alloy in order to improve its behavior in a severe corrosive environment.SOLUTION: The present invention relates to a brazing sheet comprising: a core layer made of a AA3xxx alloy comprising, in weight percentages: up to 0.70% Si, up to 0.70% Fe, 0.20 to 1.10% Cu, 0.70 to 1.80% Mn, up to 0.40% Mg, up to 0.30% Zn, up to 0.30% Ti, Zr and / or Cr and / or V each up to 0.30%, other elements less than 0.05% each and less than 0.15% in total, balance being Al; a brazing layer, made of a AA4xxx alloy which is present on at least one side of the core layer; and an interlayer, inserted between the core layer and the brazing layer, on at least one side of the core layer, which composition comprises, in weight percentages: from 1.5 to 2.3% Zn, from 0.2 to 0.45% Mn, up to 0.5% Fe, up to 0.5% Si, other elements less than 0.05% each and less than 0.15% in total, balance being Al.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an aluminum brazing sheet to be used in a heat exchanger system, such as a heat exchanger for an automobile. The brazing sheet is ideally used to fabricate tubes or plates of such heat exchangers. The heat exchanger can be, for example, an air intake cooler (CAC), an exhaust gas recirculation (EGR) cooler, an evaporator, a condenser or a radiator.

[0002] The present invention particularly relates to a new solution for a brazing sheet for charge air cooler (CAC) applications (see FIGS. 1 and 2). During use, the CAC heat exchanger is exposed to irritating acidic condensate from a mixture of compressed exhaust gas and air during cooling, which requires an aluminum brazing sheet with even higher corrosion resistance.

Background Art

[0003] Heat exchangers for the automotive industry are today mainly made of aluminum alloys, mainly because of their low density, which allows weight reduction, especially compared to copper alloys, while ensuring excellent heat conduction, ease of use and excellent corrosion resistance.

[0004] As will be apparent in the following description, all alloy and quality designations refer to the Aluminum Association designations in Aluminum Standards and Data and the Registration Records, published by the Aluminum Association of the United States, unless otherwise indicated.

[0005] A heat exchanger generally includes tubes or pairs of plates stacked vertically for the circulation of an internal fluid, fins for increasing heat transfer between the internal fluid and an external fluid, and any turbulators inside the tubes or pairs of plates that serve the same purpose as the fins. For CAC applications, the internal fluid can be a gas or refrigerant to be cooled, depending on the configuration. The internal fluid flows through the tubes or through the flow paths formed by the pairs of plates. The external fluid can be air or a gas to be cooled, depending on the configuration. The external fluid flows between the tubes or between the pairs of plates and also through any fins.

[0006] For radiator applications, the internal fluid is the fluid to be cooled and the external fluid is air.

[0007] For evaporator applications, the internal fluid is a refrigerant and the external fluid is air to be cooled for air conditioning.

[0008] The fabrication of a heat exchanger is carried out by mechanical assembly or brazing. The first step of the fabrication process is to manufacture a sheet, which is then used to obtain tubes or plates. Tubes are generally obtained by sheet roll forming and welding or brazing. Plates are generally obtained by punching the sheet. Two plates form a pair to create a flow path through which a fluid can flow.

[0009] The normal configuration of a brazing sheet is as follows. That is, a core layer generally made of an AA3xxx series aluminum alloy is clad on one or both sides with a so-called brazing layer of generally an AA4xxx series. The brazing layer has the advantage of melting at a temperature lower than the melting temperature of the core layer, so that by applying a brazing heat cycle, a bond between the two materials to be assembled can be created.

[0010] The three-layer structure is shown in Figure 3, where the core layer is labeled with reference numeral 2, and the brazing layer is labeled with reference numeral 1. The brazing layer may have the same or different compositions. The fins are positioned between different rows of tubes or between different rows of pairs of plates (i.e., outside the tubes or pairs of plates), are made of an AA3xxx series alloy, and the alloy may or may not be clad. Brazing of the fins to the tubes or pairs of plates is ensured by a brazing layer made of an AA4xxx series, which is positioned outside the tubes or pairs of plates. The AA3xxx series alloy used for the core layer of the tubes or plates is in most cases made of a so-called "long life" alloy, i.e., an alloy with excellent resistance to external corrosion by salt.

[0011] However, the general three-layer brazing sheet solution is generally not suitable for CAC type heat exchangers due to rapid corrosion penetration into the core layer of the sheet.

[0012] Generally, to improve the corrosion resistance of the brazing sheet, the solution lies in inserting an intermediate layer made of an AA1xxx series or AA7xxx series alloy between the core layer of the tubes or plates and the brazing layer made of an AA4xxx series.

[0013] Such a configuration is schematically shown in Figure 4, where the core layer of the tubes or plates is labeled with reference numeral 2, the brazing layer (which may have a similar or different composition) made of an AA4xxx series alloy is labeled with reference numeral 1, and the intermediate layer generally made of an AA1xxx series or AA7xxx series alloy is labeled with reference numeral 3.

[0014] Such an intermediate layer improves the corrosion behavior by two mechanisms. First, the intermediate layer restricts the diffusion of components (such as silicon) from the brazing layer to the core layer of the tube or plate during brazing, and also restricts the diffusion of components (such as copper) from the core layer to the brazing layer. Second, the intermediate layer provides sacrificial anode protection when the corrosion potential of the intermediate layer is lower than that of the core layer, or has higher corrosion resistance than the core layer.

[0015] These multi-layer sheets are known to those skilled in the art and are described in particular in the following patent applications. Japanese Patent Application Laid-Open No. 2003-027166 of Kobe Steel, Ltd. and Kobe Steel Alcoa Transportation Materials Co., Ltd., Japanese Patent Application Laid-Open No. 2005-224851 of Kobe Steel Alcoa Transportation Materials Co., Ltd., International Publication Nos. 2006 / 044500 and 2009 / 142651 of Alcoa Inc., International Publication No. 2007 / 042206 of Corus Aluminium Walzprodukte GmbH, U.S. Patent Application Publication No. 2010 / 0159272 of Novelis, etc.

[0016] The use of this type of multi-layer sheet in an air intake cooler with an exhaust gas passage is described in International Publication No. 2008 / 063855 of Modine Mfg Co.

[0017] This use is also described in the publication "New Advanced Materials - New Opportunities for Brazed HX Folded Tubes & Hydro MultiClad Materials", Hartmut Janssen, 7th Aluminium Brazing Conference, 2012, and also in the following patent applications, International Publication No. 2009 / 128766 of "Sapa Heat Transfer AB", International Publication No. 03 / 089237 of "Alcoa Inc.", European Patent Application Publication No. 2065180, International Publication No. 2006 / 044500, International Publication No. 2007 / 042206 of "Corus Aluminium Walzprodukte GmbH" and French Patent Application Publication No. 2876606.

[0018] However, while such a configuration can improve the corrosion resistance of the tubes or plates, it may be insufficient under particularly severe corrosion conditions, as is the case for heat exchangers that receive exhaust gas recirculation characterized by a low pH.

[0019] As a solution, it is known to use an intermediate layer containing Zn to improve the corrosion resistance of these brazing sheets. A common intermediate layer is made of, for example, AA7072 alloy or AA3003 alloy containing Zn. The Zn-containing intermediate layer serves as a sacrificial anode and forces corrosion to attack the inner surface of the heat exchanger laterally rather than penetrating into the core layer by local pitting or intergranular corrosion.

[0020] Another solution is described, inter alia, in Aleris European Patent No. 1934013, where a four-layer brazing sheet solution using two 4xxx layers, a 3xxx core layer (containing 0.55 - 1% Cu), and a 3xxx intermediate layer containing 0.1 - 5% Zn and 0.5 - 1.5% Mn is described.

[0021] Moreover, hot rolling of a multi-layer sandwich structure with an intermediate layer having a low flow stress at high temperature is very difficult. In this case, the selection of the intermediate layer needs to be made carefully so that the bonding between the intermediate layer and the surrounding layers does not become difficult or even impossible.

[0022] A solution for facilitating rolling is to increase the flow stress of the intermediate layer at high temperature, particularly by adding hardening elements. This is the case for titanium at a maximum 0.3% level as mentioned in International Publication No. 2009 / 128766 of "Sapa Heat Transfer AB". Manganese is also cited as a hardening agent by solid solution.

[0023] The above application and International Publication No. WO 2009 / 142651 of "Alcoa Inc." claim an AA3xxx alloy intermediate layer. [Prior Art Documents] [Patent Documents]

[0024] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2003-027166 [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2005-224851 [Patent Document 3] International Publication No. WO 2006 / 044500 [Patent Document 4] International Publication No. WO 2009 / 142651 [Patent Document 5] International Publication No. WO 2007 / 042206 [Patent Document 6] Specification of US Patent Application Publication No. 2010 / 0159272 [Patent Document 7] International Publication No. WO 2008 / 063855 [Patent Document 8] International Publication No. WO 2009 / 128766 [Patent Document 9] International Publication No. WO 03 / 089237 [Patent Document 10] Specification of European Patent Application Publication No. 2065180 [Patent Document 11] Specification of French Patent Application Publication No. 2876606 [Patent Document 12] Specification of European Patent No. 1934013 [Non-Patent Documents]

[0025] [Non-Patent Document 1] "New Advanced Materials - New Opportunities for Brazed HX Folded Tubes & Hydro MultiClad Materials", Hartmut Janssen, 7th Aluminium Brazing Conference, 2012

Summary of the Invention

Problems to be Solved by the Invention

[0026] The main object of the present invention is to optimize the composition of a multilayer composite material or a multilayer brazing sheet made of an aluminum alloy, in particular the composition of the core layer and the intermediate layer, while allowing manufacturing conditions that have no excessive use of materials, no large weight, and are at least equivalent to the prior art solutions from the viewpoints of ease of implementation and cost, and to improve the behavior in a severe corrosive environment such as that created by the recirculation of automotive exhaust gases and, to a lower level, by the evaporator for air conditioning.

[0027] Another object of the present invention is to optimize the sacrificial properties of the intermediate layer and thus enhance the lateralization of corrosion on the surface of the sheet and thus delay the penetration of corrosion into the core layer as much as possible.

[0028] The corrosion behavior of the brazing sheet can be evaluated by a specific cyclic corrosion test using a synthetic acidic condensate, called the "CAC test". This test is described in the following examples.

[0029] As described above, the general three - layer brazing sheet solution is generally not suitable for CAC - type heat exchangers due to the rapid corrosion penetration into the core layer of the sheet. To meet the corrosion conditions of CAC, a four - layer solution has been developed in which a sacrificial intermediate layer is added between the 4xxx brazing layer and the core layer. However, it remains difficult to obtain a sheet that is corrosion - resistant and at the same time suitable for hot rolling.

Means for Solving the Problems

[0030] The applicant has developed a multi-layer brazing sheet that enables optimization of the sacrificial aspect of the intermediate layer compared to the core layer by adding Zn to the intermediate layer containing Mn. This newly developed intermediate layer contains sufficient Mn to enable hot rolling of the sheet and shows an improvement in corrosion resistance in the CAC test compared to existing solutions.

[0031] One object of the present invention is a brazing sheet comprising, preferably consisting essentially of, more preferably consisting of: - A core layer made of an AA3xxx alloy containing, by weight, up to 0.70% (preferably 0.10 - 0.30%) of Si, up to 0.70% (preferably up to 0.40%, more preferably up to 0.25%) of Fe, 0.20 - 1.10% (preferably 0.30 - 1.00%) of Cu, 0.70 - 1.80% (preferably 1.10 - 1.60%) of Mn, up to 0.40% (preferably up to 0.30%) of Mg, up to 0.30% (preferably up to 0.20%) of Zn, up to 0.30% (preferably up to 0.20%) of Ti, each up to 0.30% of Zr and / or Cr and / or V, each other element less than 0.05% and in total less than 0.15%, the balance being aluminum, - A brazing layer made of an AA4xxx alloy (e.g., AA4343 or AA4045, preferably containing 5 - 13% by weight of Si) on at least one side (preferably both sides) of the core layer, and - An intermediate layer inserted between the core layer and the brazing layer on at least one side (in one embodiment both sides) of the core layer, the composition of which, by weight, is 1.5% to 2.3% of Zn, 0.2% (preferably 0.3%) to 0.75% (preferably 0.45%) of Mn, up to 0.5% (preferably 0.4%) of Fe, up to 0.5% (preferably 0.4%) of Si, each other element less than 0.05% and in total less than 0.15%, the balance being aluminum (preferably consisting essentially of them, more preferably consisting of them).

[0032] Another object of the present invention is the use of the brazing sheet according to the invention for the manufacture of heat exchangers for motor vehicles, preferably charge air coolers (CAC), exhaust gas recirculation (EGR) coolers, evaporators, condensers or radiators.

[0033] Another object of the present invention is the use of the brazing sheet according to the invention for the manufacture of a heat exchanger, wherein the heat exchanger is a water-cooled charge air cooler comprising a flow path formed by a tube or a pair of plates through which the gas to be cooled flows outside, the tube or plate being made of the brazing sheet according to the invention with an intermediate layer located on the outside and fixed to the outside, and comprising fins made of an aluminum alloy having a Zn content of 1.25% to 3.00% by weight, and the Zn content of the intermediate layer being less than 120%, preferably less than 100%, of the Zn content of the fins.

[0034] Another object of the present invention is a motor vehicle heat exchanger, preferably a charge air cooler (CAC), an exhaust gas recirculation (EGR) cooler, an evaporator, a condenser or a radiator, more preferably a charge air cooler, characterized in that it is partially manufactured from the brazing sheet according to the invention.

[0035] Another object of the present invention is a heat exchanger as described above, wherein the heat exchanger is a water-cooled charge air cooler comprising a flow path formed by a tube or a pair of plates through which the gas to be cooled flows outside, the tube or plate being made of the brazing sheet according to the invention with an intermediate layer located on the outside and fixed to the outside, and comprising fins made of an aluminum alloy having a Zn content of 1.25% to 3.00% by weight, and the Zn content of the intermediate layer being less than 120%, preferably less than 100%, of the Zn content of the fins. BRIEF DESCRIPTION OF THE DRAWINGS

[0036]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

DETAILED DESCRIPTION OF THE INVENTION

[0037] [Core layer] The core layer is made of a 3xxx alloy.

[0038] The core layer preferably contains the following by weight %, more preferably consists essentially of the following: Si up to 0.70%, preferably 0.05 - 0.35%, more preferably 0.10 - 0.30%, Fe up to 0.70%, preferably up to 0.40%, more preferably up to 0.25%, Cu 0.20 - 1.10%, preferably 0.30 - 1.00%, more preferably 0.35 - 0.60%, Mn 0.70 - 1.80%, preferably 1.10 - 1.60%, more preferably 1.20 - 1.50%, Mg up to 0.40%, preferably up to 0.30%, more preferably up to 0.15%, even more preferably up to 0.10%, Zn up to 0.30%, preferably up to 0.20%, Ti of up to 0.30%, preferably up to 0.20%, more preferably 0.01 - 0.20%, even more preferably 0.02 - 0.15% Zr and / or Cr and / or V of up to 0.30% each, preferably 0.01 - 0.30%, more preferably 0.02 - 0.25% Other elements each less than 0.05% and in total less than 0.15% The balance is aluminum.

[0039] The core layer of the brazing sheet according to the present invention preferably contains 0.40 - 0.54% by weight, more preferably 0.45 - 0.51% by weight of Cu.

[0040] Three suitable core layer alloys according to the present invention are described in Table 1 below in % by weight.

[0041]

Table 1

[0042] According to one embodiment, a suitable core layer alloy according to the present invention is composed of, in % by weight, 0.05 - 0.35% of Si, up to 0.40% of Fe, 0.25 - 0.70% of Cu, 1.10 - 1.60% of Mn, up to 0.15% of Mg, 0.01 - 0.30% of Cr, up to 0.30% of Zn, 0.01 - 0.20% of Ti, other elements each less than 0.05% and in total less than 0.15%, and the balance is aluminum.

[0043] The temper of the core layer can be a recovered structure such as partially annealed H24, or a fully annealed temper O. As is generally known to those skilled in the art, the temper is defined, for example, in standard BS EN 515.

[0044] 〔Brazing layer〕 The Si content of the brazing layer is preferably 5 - 13% by weight.

[0045] The composition of the brazing layer is preferably AA4045 or AA4343.

[0046] The AA4045 composition contains, for example, by weight, 9-11% Si, up to 0.8% Fe, up to 0.30% Cu, up to 0.05% Mn, up to 0.05% Mg, up to 0.10% Zn, up to 0.20% Ti, other elements each less than 0.05% and in total less than 0.15%, and the balance aluminum.

[0047] The AA4343 composition contains, for example, by weight, 6.8-8.2% Si, up to 0.8% Fe, up to 0.25% Cu, up to 0.10% Mn, up to 0.05% Mg, other elements each less than 0.05% and in total less than 0.15%, and the balance aluminum.

[0048] According to one embodiment, the core layer is grade H24, and the brazing layer is present only on one side of the core layer, preferably on the intermediate layer side.

[0049] The brazing layer is preferably on both sides of the core layer, on top of the intermediate layer if present, or directly on the core layer otherwise, and both brazing layers have the same or different compositions.

[0050] 〔Intermediate layer〕 The intermediate layer according to the present invention contains the following by weight, is preferably substantially composed of the following, and more preferably is composed of the following: 1.5% to 2.3% Zn, 0.2% (preferably 0.3%) to 0.75% (preferably 0.45%) Mn, up to 0.5% (preferably 0.4%) Fe, up to 0.5% (preferably 0.4%) Si, other elements each less than 0.05% and in total less than 0.15%, and the balance aluminum.

[0051] The Mn content of the intermediate layer of the brazing sheet according to the present invention is preferably 0.3-0.4% by weight. The effect of this specific range of Mn in the intermediate layer is shown by the following examples.

[0052] The Zn content of the intermediate layer of the brazing sheet according to the present invention is preferably 1.5 to 2.3% by weight. The effects of this specific range of Zn in the intermediate layer are shown by the following examples.

[0053] The ratio of Zn / Mn in the intermediate layer is preferably from 2 to 11, more preferably from 3 to 7.

[0054] Ti may increase the corrosion potential and thus can make the sacrificial degree of the intermediate layer lower than that of the core layer. Therefore, the Ti content in the intermediate layer is preferably less than 0.05% by weight.

[0055] The thickness of the intermediate layer is preferably at most 65 μm, more preferably at most 55 μm.

[0056] According to one embodiment, the brazing sheet according to the present invention is used in a water-cooled air intake cooler, as shown, for example, in FIG. 2. In this specific embodiment, the intermediate layer is on the outside of the tube or pair of plates, and the fins are fixed to the outside. In this case, the outside of the tube or pair of plates is the side that contacts the gas to be cooled. In this embodiment, the Zn content of the intermediate layer is preferably less than the Zn content of the fins. This specific embodiment will be further described below.

[0057] [Sheet] The brazing sheet according to the present invention is preferably characterized in that the brazing layer and the intermediate layer each have a thickness of 3 to 30%, preferably 5 to 15%, more preferably 8 to 12% of the total thickness of the brazing sheet.

[0058] The present invention resides in the wise selection of the alloys of the core layer, the intermediate layer and the brazing layer for producing a multi-layer type brazing sheet adapted to the severe corrosion conditions that the material undergoes during use, particularly in an air intake cooler or an air-conditioning evaporator.

[0059] The concentration ranges imposed on the constituent elements of the alloy of the intermediate layer are explained, inter alia, by the following reasons: - Si has an adverse effect on pitting corrosion resistance and / or intergranular corrosion resistance. For this reason, its content must be less than 0.5% by weight, preferably less than 0.4% by weight. - Fe is generally considered an impurity for aluminum and also constitutes a preferential site for the initiation of pitting corrosion. For this reason, its content must be less than 0.5% by weight, more preferably less than 0.4% by weight. - Cu also raises the corrosion potential and thus reduces the sacrificial anode effect of the intermediate layer. Since its distribution within the alloy is not homogeneous, there is also a possibility of increasing the risk of galvanic corrosion, especially at the grain boundaries of Al 2 The presence of the Cu type of phase can also act favorably on intergranular corrosion. For this reason, its content must be limited to less than the impurity content, i.e., less than 0.05% by weight. - Mn is a hardening element and has a positive effect on the strength after brazing by hardening in solid solution and in the form of finely dispersed particles. Most importantly, Mn improves the hot flow stress of the alloy and greatly facilitates co-rolling. However, if there is too much Mn, the corrosion attack cannot be directed laterally and is not maintained at the intermediate layer level, and the core layer may be attacked by corrosion, so the corrosion resistance decreases in this regard. Moreover, if there is too much Mn, the sacrificial degree of the intermediate layer becomes lower than that of the core layer. - Mg has a positive effect on mechanical strength but is harmful to brazability because it moves to the surface of the brazed layer. Especially in the case of "Nocolok (registered trademark)" type controlled atmosphere brazing (CAB), it forms an oxide layer that modifies the brazing characteristics in an adverse direction. For such reasons, for such difficult fields of use, its content can be restricted to 0.02% or even 0.01%. - Zn affects the corrosion resistance. Its content must be balanced with the content of Mn. If there is too much Zn, the corrosion potential of the intermediate layer may be excessively low. In this case, the intermediate layer may deteriorate excessively rapidly, especially when the intermediate layer is located on the fin side, the intermediate layer may corrode faster than the fin (which is supposed to be protective). The content of Zn in the intermediate layer is therefore preferably from 1.5% to 2.3% by weight.

[0060] The presence of the intermediate layer makes it possible to create a decrease in the copper profile from the core layer to the brazing layer. As a result, the effect of zinc on the corrosion resistance is enhanced.

[0061] The core layer side on the side opposite to the intermediate layer side may be directly clad with a brazing layer made of an AA4xxx series alloy. The brazing layer may have the same or different compositions.

[0062] However, an advantageous variant of this configuration is a symmetric multilayer composite material, i.e., with intermediate layers on both sides of the core layer, one ensuring resistance to internal corrosion and the other ensuring resistance to external corrosion, which is very advantageous in the case of a CAC type heat exchanger. Also in this embodiment, the brazing layer may have the same or different compositions. This also applies to the two intermediate layers.

[0063] 〔Manufacturing process〕 The brazing sheet according to the invention may be manufactured using any known process. The process may generally include the following successive steps: - Casting various alloys to obtain blocks, - Scalping the blocks on both sides, - Optionally homogenizing the intermediate layer, - Preheating the blocks of the brazing alloy and the intermediate layer alloy at 400 - 550 °C, - Hot rolling the blocks of the brazing alloy and the intermediate layer alloy to the desired clad thickness to obtain the desired clad ratio, - Homogenize the ingots of the core layer alloy arbitrarily at 550 - 630 °C for at least 1 hour, preferably between 1 and 20 hours. - Assemble the ingots to obtain a sandwich structure. - Preheat the sandwich structure at 400 - 550 °C. - Hot roll the sandwich structure to an intermediate thickness, for example 2 - 4.5 mm. - Cold roll the hot - rolled sandwich structure to a desired final thickness, for example 0.15 - 1.20 mm, to obtain a brazing sheet. - Anneal at 250 - 450 °C for at least 30 minutes.

[0064] The goal of the annealing step is to achieve a desired quality classification, for example H24 or quality - sorted O.

[0065] Then the brazing sheet can be brazed to other sheets which may have the same or a different configuration. The brazing process preferably uses a flux, which is a known process called, for example, Nocolok®.

[0066] Such brazing sheets are particularly suitable for the manufacture of heat exchangers, preferably charge air coolers (CACs), exhaust gas recirculation (EGR) coolers, evaporators, condensers or radiators, more preferably charge air coolers (CACs), because of their excellent behavior, especially in punching, and significantly improved corrosion behavior, as shown in the following examples.

[0067] The present invention constitutes the best compromise between rolling formability and corrosion resistance. The present invention is different from the known prior art, at least in terms of the specific selection of the total amount of Mn and Zn in the intermediate layer.

[0068] [Usage] The brazing sheet according to the present invention can be used in the manufacture of automotive heat exchangers, preferably charge air coolers (CACs), exhaust gas recirculation (EGR) coolers, evaporators, condensers or radiators, more preferably charge air coolers (CACs). As is known, there are two main types of CACs, namely air-cooled CACs and water-cooled CACs.

[0069] The air-cooled CAC can be illustrated in FIG. 1. FIG. 1 shows a schematic longitudinal cross-sectional view of the tubes of an air-cooled charge air cooler (air-cooled CAC).

[0070] The tubes of the air-cooled CAC as illustrated in FIG. 1 are made of a four-layer brazing sheet. The brazing sheet includes two brazing layers 1 that may have the same or different compositions, a core layer 2, and an intermediate layer 3. Reference numeral 4 represents the fins. It is understood that according to another embodiment, the brazing sheet may include a second intermediate layer having the same or different composition on the opposite side compared to the first intermediate layer.

[0071] The gas 5 to be cooled flows through the inside 8 (= intermediate layer side) of the tube. Air 6 flows through the outside 9 (= opposite side of the intermediate layer) of the tube. The fins 4 are positioned on the outside 9 of the tube. The intermediate layer 3 is positioned on the inside 8 of the tube through which the gas 5 to be cooled flows.

[0072] The water-cooled CAC can be illustrated in FIG. 2. FIG. 2 shows a schematic longitudinal cross-sectional view of the tubes (or flow paths formed by a pair of plates) of a water-cooled charge air cooler (water-cooled CAC).

[0073] The tubes (or flow paths formed by a pair of plates) of the water-cooled CAC as illustrated in FIG. 2 are made of a four-layer brazing sheet. The brazing sheet includes two brazing layers 1 that may have the same or different compositions, a core layer 2, and an intermediate layer 3. Reference numeral 4 represents the fins. It is understood that according to another embodiment, the brazing sheet may include a second intermediate layer having the same or different composition on the opposite side compared to the first intermediate layer.

[0074] The coolant 7 flows inside 8 (opposite side of the intermediate layer) of the flow path formed by the tube or pair of plates. The gas 5 to be cooled flows outside 9 (intermediate layer side) of the flow path formed by the tube or pair of plates. The fins 4 are outside 9 of the flow path formed by the tube or pair of plates. The intermediate layer 3 is positioned outside 9 of the flow path formed by the tube or pair of plates through which the gas 5 to be cooled flows.

[0075] According to one embodiment, the brazing sheet according to the present invention can be used for the manufacture of a heat exchanger for an automobile, preferably an air intake cooler (CAC), an exhaust gas recirculation (EGR) cooler, an evaporator, a condenser or a radiator, preferably an air intake cooler (CAC).

[0076] According to another embodiment, the brazing sheet according to the present invention is a water-cooled air intake cooler in which the heat exchanger includes a flow path formed by a tube or a pair of plates through which the gas to be cooled flows outside, the tube or plate being made of the brazing sheet according to the present invention in which the intermediate layer is located on the outside and fixed to the outside, and includes fins made of an aluminum alloy having a Zn content of 1.25 wt% to 3.00 wt%, and the Zn content of the intermediate layer is less than 120%, preferably less than 100% of the Zn content of the fins, and can be used for the manufacture of a heat exchanger.

[0077] The fin alloy preferably includes a 3003 alloy to which Zn is added so that the total Zn content is 1.25 wt% to 3.00 wt%, and more preferably is composed of the alloy. The 3003 alloy generally contains, by weight, a maximum of 0.60% Si, a maximum of 0.70% Fe, 0.05% to 0.20% Cu, 1.00% to 1.50% Mn, a maximum of 0.10% Zn, other elements each less than 0.05% and a total of less than 0.15%, and the balance is aluminum.

[0078] The present invention will be better understood in its details by using the examples illustrated below, but these examples are not limiting.

[0079] All documents shown in this specification are hereby incorporated by reference in their entirety.

[0080] As used herein and in the following claims, articles such as "the", "a", and "an" can imply either the singular or plural form.

[0081] In this specification and in the following claims, for ranges of enumerated numerical values, such values are intended to refer to both the exact value and values close thereto that would amount to insubstantial variations from the recited value.

Examples

[0082] Figure 4 and Table 2 summarize the constitution and composition of the investigated materials (in weight %). All of the solutions were quality sorted with O before brazing and had a thickness of 400 microns. The thickness of the intermediate layer was 40 μm.

[0083] According to Figure 4, the brazing layer 1 was made of AA4343, occupied 7.5% of the total thickness, and was on both sides of the brazing sheet. The intermediate layer 3 occupied 10% of the total thickness, and the core layer 2 occupied 75% of the total thickness.

[0084]

Table 2

[0085] Several four-layer sheets using different core layer alloys and intermediate layer alloys were prototyped. For all of the prototyped sheets, AA4343 alloy was used as the brazing layer on both sides. The sheets shown as Example 1, Example 2, and Example 3 are according to the present invention. The sheets shown as Reference 1-Mn, Reference 2-Mn, Reference 3-Mn, and Reference-Zn are comparative examples.

[0086] The alloy of Core-1 had the following composition by weight%: Si: 0.18, Fe: 0.15, Cu: 0.65, Mn: 1.35, Ti: 0.08, other elements each less than 0.05 and in total less than 0.15, the balance being aluminum.

[0087] The alloy of Core-2 had the following composition by weight%: Si: 0.19, Fe: 0.13, Cu: 0.51, Mn: 1.33, Cr: 0.09, Zn: 0.02, Ti: 0.01, other elements each less than 0.05 and in total less than 0.15, the balance being aluminum.

[0088] The AA4343 alloy had the following composition by weight%: Si: 7.2, Fe: 0.15, Cu less than 0.1, Mn less than 0.1, Ti less than 0.05, other elements each less than 0.05 and in total less than 0.15, the balance being aluminum.

[0089] The manufacturing process of the brazing sheet was as follows: - Casting various alloys to obtain ingots, - Scalping the obtained ingots on both sides, - Preheating the ingots of the brazing alloy and the intermediate layer alloy at 500 °C, - Hot rolling the ingots of the brazing alloy and the intermediate layer alloy to the desired clad thickness to obtain the desired clad ratio, - Homogenizing the ingots of the core layer alloy at 620 °C for 8 hours, - Assembling the ingots to obtain a sandwich structure, - Preheating the sandwich structure at 500 °C, - Hot rolling the sandwich structure to a thickness of 3.5 mm, - Cold rolling to a thickness of 0.4 mm, and - Annealing at 350 °C for 1 hour to obtain Quality O.

[0090] Next, the sheet was subjected to a brazing cycle simulation involving a temperature increase to a maximum of 550 °C at a rate of 40 °C / min and then to a maximum of 600 °C at a rate of 20 °C / min. This temperature was maintained for 2 minutes. Next, cooling was carried out in the furnace at approximately -25 °C / min.

[0091] The obtained material was then subjected to a corrosion test.

[0092] 〔Corrosion Test〕 As a first rough assessment of the durability of the investigated materials in a corrosive environment, the ASTM G85A3 - SWAAT test is generally carried out in a climate chamber. The procedure is based on a cycle of 30 minutes of spraying + 90 minutes of immersion. A 5% synthetic seawater solution at pH 3 is used as the condensate. Although the SWAAT test is widely used to test heat exchangers, this procedure is associated with atmospheric corrosion and relates to the durability of the outside of heat exchangers such as evaporators for air conditioners.

[0093] For the specific case of an air intake cooler (CAC), the effect of the SWAAT test is very limited. Therefore, a specialized corrosion test was developed to simulate corrosion in the CAC heat exchanger. The exhaust gas circulating inside the CAC mainly consists of CO 2 , H 2 O, NO X and SO 2 (depending on the diesel - sulfur level). Since it has been found that when condensate formation occurs, strong acids (HNO 3 , H 2 SO 4) and low-corrosive organic acids are generated. The composition and dew point of the exhaust gas condensate depend on the fuel composition, combustion process, air ratio, engine load, treated exhaust gas, engine startup stage, etc. Moreover, the EGR (Exhaust Gas Recirculation) system will be frequently exposed to continuous wet and dry environments according to the engine speed and temperature. The state where the fluid acidic condensate remains on the components and can dry is critical. From these evaluations, a corrosion test called "CAC test" hereinafter based on a 3-step 4-hour cycle was established (see the following diagram). This corrosion test aims to evaluate the corrosion resistance seen during use, and it includes not only the spraying stage using a synthetic condensate made from an equimolar solution of sulfuric acid and nitric acid (H 2 SO 4 +HNO 3 ), but also drying and wetting cycles. The test was conducted at pH 2 and 1000 ppm Cl - for 6 weeks.

[0094] TIFF0007683063000003.tif54166

[0095] Samples of 45 mm (L) × 65 mm (TL) × 0.48 mm (TC) were cut from each reference (see Figure 5). The samples were degreased using acetone and then masked to expose only the front side to be tested. The edges and the back were protected with silicone and adhesive tape, respectively. Therefore, the test surface was about 40 mm (L) × 60 mm (TL), resulting in an exposure surface of about 2400 ± 100 mm 2 .

[0096] When the SWAAT test was completed, cross-sectional micrographs at the L-ST surface were taken to investigate the corrosion morphology of the exposed surface. As shown in Figure 6, four cross-sections of 40 mm (L) × 10 mm (TL) were cut and observed by optical microscopy using two different magnifications (i.e., ×50 and ×100) to obtain reliable photographs representing the attack mode.

[0097] The results of the observation by the optical microscope method are shown in Table 3 below.

[0098]

Table 3

[0099] In Table 3 above, “-” means the absence of lateralization of corrosion in the intermediate layer or the presence of severe corrosion in the core layer, “+” means the moderate presence of corrosion or lateralization in the core layer, and “++” means the sufficiently effective presence of lateralization of corrosion in the intermediate layer or the absence of corrosion in the core layer. The results are based on the observation of micrographs.

[0100] The results shown in Table 3 above support the lateralization of corrosion in the sacrificial intermediate layer while there is no penetration of the lower core layer for the composition according to the present invention.

Explanation of Signs

[0101] 1 Brazing layer 2 Core layer 3 Intermediate layer 4 Fin 5 Gas to be cooled 6 Air 7 Cooling liquid 8 Inside of the tube (flow path) 9 Outside of the tube (flow path)

Claims

1. Brazing sheets including: a core layer made of an AA3xxx alloy consisting of, in weight %, max 0.70% Si, max 0.70% Fe, 0.20-1.10% Cu, 0.70-1.80% Mn, max 0.40% Mg, max 0.30% Zn, max 0.30% Ti, max 0.30% Zr and / or Cr and / or V, less than 0.05% each and less than 0.15% in total of other elements, the balance being Aluminium; - a brazing layer made of an AA4xxx alloy, on at least one side of the core layer; and an intermediate layer inserted between the core layer and the brazing layer, on at least one side of the core layer, having a composition, in weight percent, of 1.5% to 2.3% Zn, 0.2% to 0.45% Mn, max 0.5% Fe, max 0.5% Si, other elements less than 0.05% each and less than 0.15% in total, the remainder being aluminum;

2. 2. The brazing sheet according to claim 1, wherein the core layer contains 0.45 to 0.51 wt % Cu.

3. 3. The brazing sheet according to claim 1, wherein the core layer is composed of, by weight percent, 0.05-0.35% Si, maximum 0.40% Fe, 0.25-0.70% Cu, 1.10-1.60% Mn, maximum 0.15% Mg, 0.01-0.30% Cr, maximum 0.30% Zn, 0.01-0.20% Ti, other elements each less than 0.05% and less than 0.15% in total, and the remainder being aluminum.

4. 4. A brazing sheet according to claim 1, characterized in that a brazing layer is present on both sides of the core layer, both brazing layers having the same or different composition.

5. 5. The brazing sheet according to claim 1, wherein the intermediate layer has a Mn content of 0.30 to 0.40% by weight.

6. 6. The brazing sheet according to claim 1, wherein the brazing layer and the intermediate layer each have a thickness of 3 to 30% of the total thickness of the brazing sheet.

7. 7. The brazing sheet according to claim 1, wherein the Zn / Mn ratio in the intermediate layer is from 2 to 11.

8. 8. A brazing sheet according to claim 1, characterized in that the thickness of the intermediate layer is at most 65 μm.

9. 9. Use of a brazing sheet according to any one of claims 1 to 8 for the manufacture of a heat exchanger for an automobile.

10. A heat exchanger for an automobile, characterized in that it is partially manufactured from a brazing sheet according to any one of claims 1 to 8.

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