Aluminum materials for fluxless CAB brazing

Abstract

An aluminum alloy brazing sheet is provided having a 3XXX, 1XXX or 6XXX core, a liner and a 4XXX brazing layer without added Mg. The liner has Bi and Mg, and the magnesium migrates to the surface of the brazing sheet during brazing and reduces the aluminum oxide to facilitate brazing without flux in a controlled inert atmosphere with reduced oxygen.

Description

[0001] Case information

[0002] This application is a divisional application of the invention patent application with application number 201880008613.6 filed on January 24, 2018 and invention name “Aluminum material for fluxless CAB brazing”.

[0003] CROSS-REFERENCE TO RELATED APPLICATIONS

[0004] This application claims the benefit of U.S. Provisional Application No. 62 / 452,090, filed on January 30, 2017, entitled “Aluminum Material for Fluxless CAB Brazing,” which is incorporated herein by reference in its entirety. Technical Field

[0005] The present invention relates to sheet metal, and more particularly, to sheet metal made of aluminum alloys for use in joining structures such as heat exchangers and heat exchanger components by controlled atmosphere brazing (CAB) in the absence of flux. Background Art

[0006] Brazing of metals is well known, wherein metal surfaces are brought into close proximity and heated in the presence of a filler metal, the filler metal is melted, flows into the interface between the adjoining parts by capillary action and hardens upon cooling to join the metal parts. In order for the brazing of aluminum parts to be successful, it is necessary to protect the surfaces to be joined and the filler metal from oxidation during the various stages in the brazing process. Vacuum brazing is a furnace joining technique that effectively removes most of the oxygen from the brazing chamber by a combination of evacuating the chamber and using an oxygen getter such as Mg to protect the parts from oxidation. The main method of furnace brazing at present is controlled atmosphere brazing (CAB), in which the parts are heated in a muffle furnace under a protective inert gas atmosphere (such as nitrogen) with a low O2 content. In CAB brazing, a flux is used to remove oxides from the parts to be joined and then protect the clean metal surfaces from oxidation due to residual O2 in the furnace atmosphere. One such flux currently in widespread use is Nocolok®. TM Flux. CAB brazing relies heavily on flux to deal with oxides on the parts and to control oxidation in the furnace, but there are several reasons to avoid using flux in CAB brazing. These reasons include environmental health and safety (EHS) concerns and problems caused by residual flux remaining on the parts after brazing. This has led to the development of materials that can be joined in a fluxless CAB brazing process.

[0007] International Patent Application Publication No. WO 2013 / 180630 (also U.S. Patent Application No. 14 / 404,093) describes a brazing sheet for fluxless CAB brazing comprising an aluminum alloy core material covered by an aluminum alloy interlayer comprising ≤1.0% Si, 0.1-2.5% Mg, the interlayer being covered by an Al-Si brazing alloy comprising 5-14% Si, 0.01-1.0% Bi, <0.8% Fe, <6% Zn, <0.1% Sn, <0.1% In, <0.3% Cu, ≤0.15% Mn and <0.05% Sr. The core material and the interlayer material have a higher melting temperature than the brazing alloy, for example, the melting point of the interlayer and the core may be >615C. The thickness of the interlayer may be 2.5% to 25% of the sheet thickness.

[0008] European patent EP 1430988B1 describes a method for brazing on the internal hollow part of a structure formed by an aluminum alloy material without applying a flux. The brazing is carried out in an inert atmosphere and the sheet used to form the hollow structure has an aluminum alloy core, which is coated with an Al-Si based brazing alloy with a thickness of "a" microns on one or both sides. The core contains X% Mg (≥0.1% Mg) and the brazing alloy contains Y% Mg, wherein the corresponding compositions of the two satisfy the following relationship: (X+Y)≤a / 60+0.5 and X>Y. A 4-layer brazing sheet structure is also disclosed, which introduces a diffusion-proof layer between the core layer and the filler layer on the outside of the formed hollow part. Despite this, alternative brazing methods and materials remain interesting. Summary of the invention

[0009] The disclosed subject matter relates to a sheet material for fluxless CAB brazing, comprising: a core layer of a 3XXX, 1XXX or 6XXX series aluminum alloy; a lining layer having 0.25 to 1.7 wt. % Mg, 0.3-1.1 wt. % Si, 0.09-0.5 wt. % Bi and aluminum; a brazing backing layer of a 4XXX aluminum alloy, wherein the lining layer is disposed between the core layer and the brazing backing layer, the core layer, the lining layer and the brazing backing layer being combined together to form the sheet material.

[0010] In another embodiment, the lining layer further comprises up to 1.8 wt% Mn, up to 0.9 wt% Cu, up to 0.7 wt% Fe, up to 0.18 wt% Ti, up to 3.0 wt% Zn, up to 0.25 wt% Cr, and up to 0.15 wt% Zr.

[0011] In another embodiment, the braze backing layer has a composition of Mg≤0.05 wt%.

[0012] In another embodiment, the braze backing layer has a composition of Bi<0.010 wt%.

[0013] In another embodiment, the core layer has 0.08-1.1 wt % Si, 0.15 to 0.7 wt % Fe, 0.05-1.0 wt % Cu, 0.4-1.8 wt % Mn, up to 0.5 wt % Mg, up to 2 wt % Zn, up to 0.25 wt % Cr, and up to 0.15 wt % Zr.

[0014] In another embodiment, the braze backing layer has 5-12 wt% Si, up to 0.7 wt% Fe, up to 3 wt% Zn, aluminum, and incidental impurities.

[0015] In another embodiment, the core has 60% to 90% of the total thickness of the sheet material, the lining layer has 3% to 20% of the total thickness, and the braze backing layer has 3% to 20% of the total thickness.

[0016] In another embodiment, the backing layer is a first backing layer and further includes a second backing layer having a composition similar to that of the first backing layer, the second backing layer being disposed on the core opposite the first backing layer.

[0017] In another embodiment, the braze backing layer is a first braze backing layer and further includes a second braze backing layer disposed on the second lining layer distal from the core.

[0018] In another embodiment, an additional aluminum alloy layer is disposed on the core opposite the liner layer, wherein the additional alloy layer is a 3XXX alloy, a 3XXX+Zn alloy, a 1XXX alloy, a 7XXX alloy, or a 4XXX alloy.

[0019] In another embodiment, a structure comprises: a first portion made of aluminum; a second portion made of the above-mentioned sheet material, the first portion and the second portion are joined together by a brazed joint formed at least in part by a braze backing layer of the second portion.

[0020] In another embodiment, the structure is part of a heat exchanger, such as an oil cooler or radiator.

[0021] In another embodiment, the heat exchanger has an interior hollow portion that is free of flux residue.

[0022] In another embodiment, Mg is present in the liner layer composition at 0.25 to .95 wt%.

[0023] In another embodiment, Mg is present in the liner layer composition at 1.0 to 1.7 wt%.

[0024] In another embodiment, Si is present in the backing layer composition at 0.3 to 0.65 wt%.

[0025] In another embodiment, Si is present in the backing layer composition at 0.7 to 1.1 wt%.

[0026] In another embodiment, Bi is present in the backing layer composition at 0.05 to 0.20 wt%.

[0027] In another embodiment, Bi is present in the backing layer composition at 0.25 to 0.50 wt%.

[0028] In another embodiment, a method for brazing includes: providing a first aluminum alloy material; providing a second aluminum alloy material, wherein the second aluminum alloy material has a core layer of a 3XXX, 1XXX or 6XXX series aluminum alloy, a lining layer of aluminum having 0.25 to 1.7 wt. % Mg, 0.3-1.1 wt. % Si, 0.09-0.5 wt. % Bi, and a brazing backing layer of a 4XXX aluminum alloy having less than 0.05% Mg and less than 0.010% Bi, wherein the lining layer is disposed between the core layer and the brazing backing layer, and the core layer, the lining layer and the brazing backing layer are combined to form a sheet material; contacting the first material with the second material, with the brazing backing layer of the second sheet facing the first sheet; and brazing the first material to the second material in an inert atmosphere brazing furnace without using a flux.

[0029] In another embodiment, the brazing step is performed in a controlled atmosphere wherein the oxygen level is reduced to a level in the range of 1 ppm to about 35 ppm.

[0030] In another embodiment, the first aluminum alloy material has the same composition as the second aluminum alloy material.

[0031] In another embodiment, the sheet material has: a core layer of a 3XXX series aluminum alloy; a lining layer of 0.25 to 1.7 wt % Mg, 0.3–1.1 wt % Si, 0.09–0.5 wt % Bi, up to 1.8 wt % Mn, up to 0.9 wt % Cu, up to 0.7 wt % Fe, up to 0.18 wt % Ti, up to 3.0 wt % Zn, up to 0.25 wt % Cr and up to 0.15 wt % Zr, with the remainder being aluminum and impurities; a brazing backing layer of a 4XXX aluminum alloy, wherein the lining layer is disposed between the core layer and the brazing backing layer, and the core layer, the lining layer, and the brazing backing layer are combined together to form the sheet material. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more fully understand the present disclosure, refer to the attached Figure 1 The following detailed description of exemplary embodiments is contemplated.

[0033] Figure 1 is a cross-section of a brazing structure according to an exemplary embodiment of the present disclosure.

[0034] Figure 2 Reason Figure 1 The enlarged fragment is indicated by the circle labeled 2.

[0035] Figure 3 is a perspective view of a brazing structure according to an exemplary embodiment of the present disclosure.

[0036] Figure 4 is a diagrammatic view of a sheet material according to the present disclosure.

[0037] Figure 5 is a diagrammatic view of one sheet material according to the present disclosure positioned adjacent to another sheet material according to the present disclosure prior to brazing. DETAILED DESCRIPTION

[0038] Figure 1 A cross section of a brazed structure 10 is shown having a pair of opposed shallow drawn cup-shaped members 12, 14 formed of sheet metal 12M, 14M such as an aluminum alloy, brazed along a circular seam formed along the mating tracks of the cups, shown at joints 16, 18 to form the structure 10 having an internal hollow portion 20. Although Figure 1 Two joints 16, 18 are shown, but these are different areas of a single continuous joint between the components 12, 14. In the exemplary structure 10 shown, the components 12, 14 are symmetrical and similar in shape, so that the sheet metal 12M, 14M can have the same composition and thickness. In other applications, for example, when joining a tube structure to a sheet metal header (not shown), the sheet metal of the header will have a different structural shape and may have a different composition and / or thickness. A plurality of fins 22 are attached to the opposing components 12, 14, for example by brazing, and span the hollow portion 20. Since the components 12, 14 are cup-shaped in cross-section, they can be referred to as "cups" and the overall structure 10 is referred to as a "cup / cup structure". The peripheral flange portions 12F, 14F of the components 12, 14 brazed together at the joints 16, 18 can be referred to as "tracks". This particular sample geometry is used as a convenient tool for material evaluation during product development.

[0039] In commercial applications, this product may be used to produce a tube sheet structure that can be used in a stacked plate oil cooler or as a tubular structure, such as a tube in an automobile radiator. The test structure 10 is only a very simple example of a structure that can be formed by brazing sheet metal according to the present disclosure. The sheet metal 12M, 14M of each member 12, 14 has two surfaces 12S1, 12S2 and 14S1, 14S2, respectively. In the structure 10 shown, 12S1, 14S1 form the surface outside the hollow portion 20, while 12S2, 14S2 form the internal surface, wherein 12S2 and 14S2 form brazed joints 16, 18 with each other and with the fin 22. For this reason, the surfaces 12S2, 14S2 intended to form a brazed joint may have a specific composition to support brazing. In another alternative, the surface 12S1 and / or 14S1 may also be intended to be brazed to another element such as an adjacent tube, an external fin or a collecting tank (not shown) and may also be dedicated to brazing.

[0040] Figure 2 An enlarged fragment of the structure 10 is shown, in which the filler metal 24 making the joint 18 is seen bridging between the components 12, 14. As the components 12, 14 diverge on either side of the joint 18, the balance between the self-attraction of the liquid filler metal 24 and the attraction of the filler metal to the surfaces 12S2 and 14S2 pulls the filler metal into the radius RE (the radius outside the hollow 20) and RI (the radius inside the hollow 20). These radii are a quantifiable measure of the effectiveness of the joint. Another quantifiable measure of the quality of the joint is the width of the joint 18W. As will be explained below, the components 12, 14 are provided in a pre-brazed state, in which the discrete layers have different compositions and include a brazing backing layer on the surfaces 12S2, 14S2, which will melt the filler metal 24 and provide it to the joint 18.

[0041] Figure 3 A structure 100 is shown having end plates 110, 112 brazed to a U-shaped intermediate member 114 at joints 116, 118. The brazed joints 116, 118 have filler metals 116M, 118M that "wet" the inner and outer surfaces 114I, 114E of the intermediate member 114 and whose ends (at joints 116 and 118) are in contact with the members 110 and 112 at the inner surface of 110 (not visible in this view) and the inner surface of 112, i.e., 112I. In the structure 100, the surfaces 112I and 110I are covered by a brazing pad that provides filler metal to the joint. Optionally, one or more of the surfaces 114E, 114I and the surface of the member 110 in contact with the intermediate member 114 may be provided with a brazing pad, as described below with reference to Figure 4 described.

[0042] Figure 4A metal sheet 200 having a plurality of layers 210, 212, 214, 216, 218 is shown, which may be used as a material for manufacturing a structure, such as Figure 1 The cup-shaped structure 10 of the present invention is a brazing structure 10, or any other structure formed by brazing a plurality of separate metal parts, wherein at least one of the metal parts is a part made of a metal sheet 200. Since the sheet 200 is suitable for making a structure by brazing, it can be referred to as a "braze sheet" and can be used for fluxless CAB brazing. The core 210 (also marked as "C") is generally composed of a 3XXX series aluminum alloy. The liner layer 212 (also marked as "IA") is bonded to the core 210. In one example, the liner 212 is an aluminum alloy having 0.25 wt% to 1.7 wt% Mg, 0.3 wt% to 1.1 wt% Si, and 0.09 wt% to 0.5 wt% Bi. The liner 212 may also contain up to 1.8% Mn, up to 0.9% Cu, up to 0.7% Fe, up to 3% Zn, up to 0.18% Ti, up to 0.20% Cr, and the remainder is aluminum and incidental impurities. A brazing backing 214 (also labeled "BLA") composed of a 4XXX series aluminum alloy having typically 5% to 12% Si, up to 0.7% Fe, the remainder being aluminum and incidental impurities, is bonded to the liner 212 distal to the core 210. Up to 3% Zn may be introduced into the 4XXX series alloy of the brazing backing 214. The core 210, liner 212, and brazing backing 214 layers may be bonded by stacking of hot rolled layers and then cold rolling and heat treating the materials to produce a final laminate structure having a desired internal structure and condition, with a thickness ranging from 0.100 mm to 4.0 mm, with the core accounting for 60% to 94% of the total thickness, the liner 212 accounting for 3% to 20%, and the brazing backing 214 accounting for 3% to 20%.

[0043] In alternative embodiments according to the present disclosure, the ranges given for the compositions of the liner, core, and brazing backing include all intermediate values. For example, for a liner composition having an aluminum alloy of 0.25 wt % to 1.7 wt % Mg, 0.3 wt % to 1.1 wt % Si, and 0.09 wt % to 0.5 wt % Bi, the balance being Al and impurities, the ranges of composition may include amounts of 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.0, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.50, 1.60, 1.70, 1.80, 1.90, 2.11, 2.12, 2.13, 2.14, 2.15 %, or any intermediate value; and Bi in an amount of 0.09, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.0, or 1.1 % by weight, or any intermediate value.

[0044] In another example of an alternative embodiment according to the present disclosure, for a liner 212 that also includes up to 1.8% Mn, up to 0.9% Cu, up to 0.7% Fe, up to 3% Zn, up to 0.18% Ti, up to 0.20% Cr, the balance being aluminum and incidental impurities, these composition ranges may include amounts of 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 10, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 70, 71, 72, 73, 74, 75 8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7 or 1.8 wt % or any intermediate value of Mn; 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9 wt % or any intermediate value of Cu; 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9 wt % or any intermediate value of % by weight or any intermediate value; Zn in an amount of 0.0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, % Ti; and 0.0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19 or 0.20 wt % or any intermediate value.

[0045] In yet another example of an alternative embodiment according to the present disclosure, a braze backing 214 comprised of a 4XXX series alloy typically having 5% to 12% Si, up to 0.7% Fe, up to 3.0 wt % Zn, the balance being aluminum and other incidental impurities, may include Si in an amount of 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, 11.5 or 12.0 wt %, or any intermediate value; Fe in an amount of 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 or 0.7 wt %, or any intermediate value; and Zn in an amount of 0.0, 0.5, 1.0, 1.5, 2.0, 2.5 or 3.0 wt %, or any intermediate value.

[0046] As mentioned above, brazing sheet such as sheet 200 can be expected to be brazed to adjacent structures on one or both sides.Sheet 200 shows optional lining layer 216 and brazing backing layer 218 with dotted lines and is marked as "IB" and "BLB" to represent the optional properties of these layers, and these layers will be provided if the sheet is to be brazed on the side of these optional layers.Core 210 and layer 212 (IA), 214 (BLA) can be referred to as "A side" of sheet 200, wherein core 210 and layer 216 (IB), 218 (BLB) form "B side" of sheet 200.Or, optional layer IB and BLB can be replaced by one or more other aluminum alloy layers, and the aluminum alloy layer is designed to give specific performance attributes to the surface after brazing, such as corrosion resistance.For example, they can be replaced by another 3XXX layer, 3XXX+Zn layer, 1XXX layer, 7XXX layer or 4XXX layer.

[0047] Figure 5 Two brazing sheets 340, 342 are illustrated positioned adjacent to each other prior to brazing, with the A side of each brazing sheet facing each other at interface I. When placed in a CAB furnace having a low ambient oxygen level and subjected to heating, the opposing brazing backing layers BLA of the sheets 340, 342 will melt and combine upon solidification to form a bond at interface I that bonds the sheets 340, 342 into structure 350. Optionally, the sheets 340, 342 may be oriented so that the A side of one sheet (e.g., 340) faces the B side of the other sheet (e.g., 342). As yet another option, the B side brazing backing layer 218 ( Figure 4 ) and / or the B-side liner layer 216 layer may not be present on one or both of the sheets 340, 342, such that the brazing pad 214 of one sheet is positioned adjacent to the B-side liner layer 216 or core layer 210 of the other sheet prior to brazing. As yet another alternative, the A-side of one sheet (e.g., 340) with or without a B-side may be adjacent to a sheet 200 (e.g., 340) without a B-side. Figure 4 ) layer structure and / or another metal structure composed of the layer structure and / or the composition is positioned and brazed thereto. That is, the A side or the B side (if any) of the sheet material 200 disclosed in the present application can be brazed to the A side or the B side (if any) of another sheet material 200 as defined in the present disclosure or to other materials not described herein.

[0048] The core layer 210 is most commonly a 3XXX series aluminum alloy. The composition of the core alloy is not particularly limited. A wide range of 3XXX core alloys can be used. The permissible composition of the 3XXX core alloy includes 0.08 to 1.1 wt % Si, 0.15 to 0.7 wt % Fe, 0.05 to 1.0 wt % Cu, 0.4% to 1.8 wt % Mn, up to 0.5 wt % Mg, up to 2 wt % Zn, up to 0.25 wt % Cr, up to 0.15 wt % Zr. As described above with respect to the liner, the composition amount of the alternative embodiment of the core can gradually change within the composition range of each element. It should be noted that other core alloys can be effective in this structure. If strength is not important, 1XXX alloys can be used. For some applications requiring high strength, 6XXX alloys can be used as core alloys.

[0049] The one or more lining layers 212, 216 that help promote fluxless brazing contain Mg, which will diffuse to the sheet surface by the molten filler metal and reduce the aluminum oxide at the surface. The Mg content of the lining alloy is between 0.25 wt% and 1.7 wt%. If the Mg is less than 0.25 wt%, it is not enough to promote brazing, but no additional benefit is found above 1.7% Mg. Si is also an important component of the one or more linings 212, 216 because it helps control the solidus temperature of the lining. The Si content of the lining 212, 216 is between 0.3 wt% and 1.1 wt%. Bismuth is also an important component of the lining because it helps promote wetting of the filler metal. If Bi is less than about 0.09 wt%, its effect on brazing is not significant, but no additional benefit is found above about 0.5 wt%. Other elements can be introduced into the lining alloy to improve post-braze strength or enhance corrosion resistance. These elements include up to 1.8 wt% Mn, up to 0.9 wt% Cu, up to 0.7 wt% Fe, up to 0.18 wt% Ti, up to 3 wt% Zn, up to 0.25 wt% Cr, and up to 0.15 wt% Zr. The liner thickness may range from 3% to 20% of the thickness of the final composite.

[0050] The brazing filler metal is a typical CAB brazing alloy such as AA4343, AA4045, AA4047, etc., without intentional Mg or Bi additions. Up to 3 wt. % Zn may be introduced into the brazing backing to provide corrosion protection to the final brazed product. The thickness of the brazing backing may range from 3% to about 20% of the final composite thickness.

[0051] This disclosure uses standard abbreviations for elements appearing in the periodic table, such as Mg (magnesium), O (oxygen), Si (silicon), Al (aluminum), Bi (bismuth), Fe (iron), Zn (zinc), In (indium), Cu (copper), Mn (manganese), Sr (strontium), Ti (titanium), Zr (zirconium), etc.

[0052] The accompanying drawings constitute a part of this specification and include illustrative embodiments of the present disclosure and illustrate various objects and features thereof. In addition, any measurements, specifications, and the like shown in the drawings are intended to be illustrative rather than limiting. Therefore, the specific structural and functional details disclosed herein should not be understood as limiting, but merely as a representative basis for teaching those skilled in the art to utilize the present invention in different ways.

[0053] Among those benefits and improvements that have been disclosed, other objects and advantages of the present invention will become apparent from the following description in conjunction with the accompanying drawings. Detailed embodiments of the present invention are disclosed herein; however, it should be understood that the disclosed embodiments are merely illustrative of the various forms in which the present invention may be implemented. In addition, each embodiment given in conjunction with the various embodiments of the present invention is intended to be illustrative and not limiting.

[0054] Throughout the specification and claims, unless the context clearly dictates otherwise, the following terms take the meanings explicitly associated herein. As used herein, the expressions "in one embodiment" and "in some embodiments" do not necessarily refer to the same or the same embodiments, although they may refer to the same or the same embodiments. In addition, as used herein, the expressions "in another embodiment" and "in some other embodiments" do not necessarily refer to different embodiments, although they may refer to different embodiments. Therefore, as described below, various embodiments of the present invention can be easily combined without departing from the scope or spirit of the present invention.

[0055] In addition, unless the context clearly dictates otherwise, as used herein, the term "or" is an inclusive "or" operator and is equivalent to the term "and / or". Unless the context clearly dictates otherwise, the term "based on" is not exclusive and allows for being based on other factors not described. In addition, throughout the specification, the meaning of "a", "an" and "the" includes plural references. The meaning of "in..." includes "in..." and "on...".

[0056] Examples and test results

[0057] To determine the efficacy of the sheet 200 described above for promoting brazing, tests were conducted. Two internal tests were conducted to measure the effectiveness of the material in fluxless CAB brazing. The first was called a cup / cup brazing test, in which two sheet metal structures that had been stamped into shallow cup-shaped articles were brazed together in CAB brazing. The brazing furnace used typically had about 50 ppm of O2 in a muffle furnace atmosphere over the critical brazing temperature range (577° to 600°C). Figure 1A cross section of a typical cup / cup brazed sample structure 10 is shown. To evaluate the quality of the joints 16, 18 (actually continuous peripheral joints), the peripheral track / track joints of these samples were sectioned at 5 or 6 different locations and various parameters of the brazed joint were measured, including the internal fillet radius (RI), external fillet radius (RE) and joint width (see Figure 2 ). In addition, a qualitative rating was given to the quality of the internal joint between the exposed 3003 fins 22 and the inner surfaces 12S2, 14S2 of the cup.

[0058] The second test involved placing the U-bend 114 ( Figure 3 ) are flux-free brazed to two sheets 110, 112 of the test material. Figure 3 A representative brazed coupon structure 100 is shown. The brazing is performed in a quartz furnace where a controlled amount of oxygen (O2) can be introduced into a nitrogen (N2) atmosphere. The quality of the joint is quantified by visual inspection and the amount of good joint length is measured relative to the amount of total possible joint length. The assumption is that "better quality" or more efficient materials can produce acceptable joints at higher O2 contamination levels than "lower quality" materials.

[0059] Some tests are described below which illustrate the brazing properties of the inventive material. Table 1 below lists the compositions of the core and liner alloys used in this work. The brazing backing in all cases was AA4045 with compositional limitations as described in the Aluminum Association's Teal Sheets.

[0060] Table 1: Core and liner alloy compositions used in the tests

[0061]

[0062]

[0063] Test 1

[0064] In one set of tests, the brazing properties of various laboratory made experimental materials were evaluated. Prior to brazing, the materials were all in the O-temperature and are described in Table 2. The coverage of the braze backing and liner is shown in parentheses as a percentage of the sheet thickness.

[0065]

[0066] Cup / cup samples were brazed in a CAB furnace using each of the above materials. For the first two materials, cup / cup samples were brazed with and without flux. Table 3 reports the average fillet size measured for each material.

[0067]

[0068] From Table 3 we can see that in standard CAB brazing (with flux), R I and R E Roughly equal, both are fairly large fillet radii and the joint widths for this geometry sample are in the 3000-3500 micron range. These fillet dimensions represent the "target" we would like to approach, but without the use of flux. In the absence of flux, the Mg-free materials 13-242-2 and 14-157-3 do not support joint formation. For material 15-128-2, where Mg, Si, and Bi were introduced into the liner between the core and the braze pad, the internal fin / cup joint is good, with R I Good, while R E The fillet width is better than that of the unlined material, although still smaller than that of the joint with flux.

[0069] Test 2

[0070] The second test was conducted with the laboratory made O-state materials listed in Table 4. Four of these were asymmetric composites.

[0071]

[0072] In all cases, when stamping and brazing cups from asymmetric materials, we brazed side A against side A or side B against side B. The results of the cup / cup brazing tests are shown in Table 5.

[0073]

[0074]

[0075] From Table 5 we see that the material incorporating a Bi-free liner (14-120-3) gives significantly smaller fillet radius and fillet length despite having high filler metal coverage. Other materials containing Mg, Si, and Bi all in the liner produce better fillets.

[0076] Test 3

[0077] A third test was conducted using the laboratory made O-state material listed in Table 6.

[0078]

[0079] These materials were brazed to bare 3003 U-bend strip in a quartz furnace with different O2 levels in a N2 atmosphere. The quality of the joint was evaluated and quantified. The results are reported in Table 7. Blank indicates that this material / atmosphere combination was not tested.

[0080]

[0081]

[0082] The quality % rating represents the percentage of good joints formed. The rating has two parts. Part A is worth 20% and is determined only by the length of the joint between the 3003 U-bend and the brazing sheet piece. The potential joint length is 80mm, so if there is no gap between the U-bend and the sheet, Part A scores 20%. Part B is worth 80% and is concentrated on the fillet radius along the joint. It is only the ratio of the length of a good fillet radius divided by the total possible fillet radius length (160mm). Therefore, if both the top and bottom parts are brazed to the U-bend and have a 130mm good fillet radius length, then the score is (80 / 80)*20%+(130 / 160)*80%=85%. The data in Table 7 clearly show the benefits of the Al-Mg-Si-Bi lining located between the core and the brazing pad in an inert atmosphere with low to medium O2 content in the absence of flux to promote good joint formation.

[0083] The sheet material according to the present disclosure can allow heat exchanger manufacturers to produce brazed heat exchangers with high internal cleanliness levels to meet the needs of their customers, especially automotive OEMs. Although vacuum brazing is a way to produce very clean internal units, not all heat exchanger manufacturers have vacuum brazing equipment. Most have CAB brazing furnaces and prefer to use them because they are easy to operate and maintain. However, the flux commonly used in CAB brazing can cause residues to be present throughout the heat exchanger after brazing. For many mass-produced heat exchangers, it is believed that the acceptable level of flux residue is decreasing. Therefore, it is desirable to have a material that can be brazed in an inert furnace atmosphere without the need for flux. Eliminating the flux also brings cost savings and increases the cleanliness of the brazing furnace area by eliminating the fluxing operation and reduces the maintenance time of the brazing muffle furnace, belts and fixtures. The sheet material according to the present disclosure can also lead to a reduction in EHS problems because the flux may cause health problems due to inhalable fine particulate material.

[0084] Although several embodiments of the present invention have been described, it should be understood that these embodiments are illustrative only and not limiting, and that various modifications may be apparent to those skilled in the art. In addition, the various steps may be performed in any desired order (and any desired steps may be added and / or any desired steps may be eliminated). All such changes and modifications are intended to be included within the scope of the claims.

Claims

1. A sheet material for flux-free CAB brazing, the sheet material comprising: A core layer, wherein the core layer is composed of a 3XXX, 1XXX or 6XXX series aluminum alloy; A lining layer consisting of 0.3 to 1.7 wt % Mg, 0.3-0.9 wt % Si, 0.1-0.5 wt % Bi and aluminum; A brazing backing layer is comprised of a 4XXX aluminum alloy, wherein the lining layer is disposed between the core layer and the brazing backing layer.

2. A sheet material for flux-free CAB brazing, the sheet material comprising: A core layer, wherein the core layer is composed of a 3XXX, 1XXX or 6XXX series aluminum alloy; a lining layer consisting of 0.3 to 1.7 wt% Mg, 0.3 to 0.9 wt% Si, 0.1 to 0.5 wt% Bi, up to 1.8 wt% Mn, up to 0.9 wt% Cu, up to 0.7 wt% Fe, up to 0.18 wt% Ti, up to 3.0 wt% Zn, up to 0.25 wt% Cr and up to 0.15 wt% Zr, and aluminum; A brazing backing layer is comprised of a 4XXX aluminum alloy, wherein the lining layer is disposed between the core layer and the brazing backing layer.

3. The sheet material according to claim 1 or 2, wherein the brazing backing layer has a composition of Mg≤0.05 wt.%.

4. The sheet material according to claim 1 or 2, wherein the brazing backing layer has a composition of Bi ≤ 0.010 wt%.

5. The sheet material of claim 1 or 2, wherein the core layer comprises 0.08-1.1 wt% Si, 0.15 to 0.7 wt% Fe, 0.05-1.0 wt% Cu, 0.4-1.8 wt% Mn, up to 0.5 wt% Mg, up to 2 wt% Zn, up to 0.25 wt% Cr and up to 0.15 wt% Zr.

6. The sheet material according to claim 1 or 2, wherein the brazing backing layer comprises aluminum and incidental impurities, 5-12 wt% Si, up to 0.7 wt% Fe, up to 3 wt% Zn.

7. The sheet material of claim 1 or 2, wherein the core layer accounts for 60% to 90% of the total thickness of the sheet material, the lining layer accounts for 3% to 20% of the total thickness, and the brazing backing layer accounts for 3% to 20% of the total thickness.

8. The sheet material according to claim 1 or 2, wherein the lining layer is a first lining layer and further comprises a second lining layer, the composition of the second lining layer being the same as that of the first lining layer, the second lining layer being arranged on the core layer opposite to the first lining layer.

9. The sheet material of claim 8, wherein the braze backing layer is a first braze backing layer and further comprising a second braze backing layer disposed on the second liner layer distal from the core layer.

10. The sheet material of claim 1 or 2, further comprising an additional aluminum alloy layer disposed on the core layer opposite the lining layer, wherein the additional aluminum alloy layer is composed of one of a 3XXX alloy, a 1XXX alloy, a 7XXX alloy, and a 4XXX alloy.

11. The sheet material of claim 1 or 2, further comprising an additional aluminum alloy layer disposed on the core layer opposite the lining layer, wherein the additional aluminum alloy layer consists of a 3XXX alloy with Zn.

12. The sheet material according to claim 1 or 2, wherein the sheet material is formed as a first portion and further comprises: The second part is made of aluminum alloy, The first portion and the second portion are joined together by a brazed joint formed at least in part by a braze backing layer of the first portion.

13. The sheet material of claim 12, wherein the sheet material is part of a heat exchanger.

14. The sheet material according to claim 12, wherein the sheet material is part of a heat exchanger and / or wherein the first part is brazed to the second part in an inert atmosphere brazing furnace without the use of a flux and / or wherein the brazing is performed in a controlled atmosphere with an oxygen level in the range of 1 ppm to 35 ppm and / or wherein the first part has the same composition as the second part.

15. The sheet material of claim 13, wherein the heat exchanger has an interior hollow portion free of flux residue.

16. The sheet material according to any one of claims 13 to 15, wherein the heat exchanger is an oil cooler or a radiator.

17. The sheet material according to claim 1 or 2, wherein Mg is present in the lining layer in an amount of 0.3 to 0.95 wt%.

18. The sheet material of claim 1 or 2, wherein Mg is present in the lining layer at 1.0 to 1.7 wt%.

19. The sheet material of claim 1 or 2, wherein Si is present in the backing layer in an amount of 0.3 to 0.65 wt%.

20. The sheet material of claim 1 or 2, wherein Si is present in the backing layer at 0.7 to 0.9 wt%.

21. The sheet material of claim 1 or 2, wherein Bi is present in the backing layer at 0.1 to 0.24 wt%.

22. The sheet material according to claim 1 or 2, wherein Bi is present in the backing layer at 0.25 to 0.50 wt%.

23. A sheet consisting of the sheet material according to any one of claims 1 to 22.

24. A method for brazing, the method comprising: (A) providing a first aluminum alloy material; (B) providing a second aluminum alloy material, wherein the second aluminum alloy material comprises: a core layer consisting of a 3XXX, 1XXX or 6XXX series aluminum alloy, a lining layer consisting of 0.3 to 1.7 wt% Mg, 0.3-0.9 wt% Si, 0.1-0.5 wt% Bi and aluminum, and a brazing backing layer comprised of a 4XXX aluminum alloy having less than 0.05 wt % Mg and less than 0.010 wt % Bi, wherein the lining layer is disposed between the core layer and the brazing backing layer; (C) contacting the first aluminum alloy material with the second aluminum alloy material, wherein the brazing backing layer of the second aluminum alloy material faces the first aluminum alloy material; (D) brazing the first aluminum alloy material to the second aluminum alloy material in an inert atmosphere brazing furnace without using a brazing flux.

25. The method of claim 24, wherein the brazing step is performed in a controlled atmosphere wherein the oxygen level is reduced to a level in the range of 1 ppm to 35 ppm.

26. The method of claim 24, wherein the first aluminum alloy material has the same composition as the second aluminum alloy material.

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