WO2018184806A1

WO2018184806A1 - Aluminium brazing sheet material suitable for fluxless brazing in a controlled atmosphere

Info

Publication number: WO2018184806A1
Application number: PCT/EP2018/056441
Authority: WO
Inventors: Steven Kirkham; Achim BÜRGER; Bernd JACOBY
Original assignee: Aleris Rolled Products Germany Gmbh
Priority date: 2017-04-04
Filing date: 2018-03-14
Publication date: 2018-10-11
Also published as: AT521441A2; AT521441B1; DE112018001845T5; AT521441A5

Abstract

The invention relates to an aluminium alloy brazing sheet product comprising a covering aluminium material layer comprising 0.5-5% Zn, an aluminium core material layer, and an Al-Si alloy brazing material layer as an intermediate material interposed between said covering aluminium material layer and said aluminium core material layer, wherein said aluminium core material layer comprising of an aluminium alloy having a solidus temperature higher than the liquidus temperature of said Al-Si alloy brazing material layer, and wherein said Al-Si alloy brazing material layer contains 0.01-1% Mg.

Description

Aluminium brazing sheet material suitable for fluxless brazing in a controlled atmosphere

FIELD OF THE INVENTION

The present invention relates to an aluminium alloy rolled brazing sheet product comprising a covering material layer, a core material layer, and further an Al-Si alloy brazing material layer as an intermediate material interposed between the covering material layer and the core material layer.

The invention further relates to a brazed assembly manufactured in a brazing operation, ideally a CAB operation without the use of a brazing flux material, the brazed assembly comprising various components and at least one component being made from the aluminium alloy rolled brazing sheet according to this invention.

BACKGROUND TO THE INVENTION

Substrates of aluminium or aluminium alloy in the form of sheet or extrusion, are used to make shaped or formed products. In some of these processes, parts of (shaped) aluminium substrates are interconnected. One end of a substrate may be interconnected with the other end, or one substrate may be assembled with one or more other substrates. This is commonly done by brazing. In a brazing process, a brazing filler metal or brazing alloy or a composition producing a brazing alloy upon heating is applied to at least one portion of the substrate to be brazed. After the substrate parts are assembled, they are heated until the brazing metal or brazing alloy melts. The melting point of the brazing material is lower than the melting point of the aluminium substrate or aluminium core sheet. Brazing sheet products find wide applications in heat exchangers and other similar equipment. Conventional brazing products have a core of rolled sheet, typically, but not exclusively an aluminium alloy of the 3xxx-series, having on at least one surface of the core sheet an aluminium clad layer. The aluminium clad layer is made of a 4xxx-series alloy comprising silicon in an amount in the range of 4% to 20%. The aluminium clad layer may be coupled or bonded to the core alloy in various ways known in the art, for example by means of roll bonding, spray-forming or semi-continuous or continuous casting processes. These 4xxx-series aluminium clad layers have a liquidus temperature typically in the range of about 540°C to 610°C.

There are various brazing processes in use for the industrial scale manufacturing of brazed assemblies such as heat exchangers.

There is vacuum brazing which is carried out at very low atmosphere pressure. To obtain the optimum conditions for joining to take place, Al-Si brazing alloys com- monly used for vacuum brazing contain purposive additions of about 1 % Mg or more. The believed mechanism is that Mg disrupts the hard oxide film of the filler alloy when it evaporates from the brazing sheet during brazing, and further, the evaporated Mg plays a role to reduce oxygen and moisture remaining in the vacuum brazing furnace.

Patent document US 3,917,151 (Kaiser Aluminum) discloses a process of vacuum brazing aluminium parts using a vacuum brazing sheet comprising an aluminium alloy core, clad to said core a brazing alloy consisting essentially of 5 to 15% Si, 0.5-5% Mg, up to 0.8% Fe, up to 0.25% Cu, up to 0.20% Zn, up to 0.20% Mn, other elements up to 0.1 % each, balance aluminium, and clad to said brazing alloy a Mg-free aluminium alloy, i.e. no more than 0.1 % Mg, with a melting point of at least 1 100°F (593°C). The Mg in the brazing alloy acts as an Mg source to facilitate the vacuum brazing process. The Mg-free alloy and the core alloy should contain less than 5% Zn, 0.8% Fe, 1 % Si, 3% Mn, 0.5% Cr, 0.05% Ti and other elements 0.10% each. Disclosed suitable alloys for the core and Mg-free alloy are 1 100 and 3003 aluminium alloys. Aluminium alloys 6951 and 7005 can also be used are core alloys. To facilitate cladding, interliners of thin, relatively pure aluminium, e.g., 1 100 alloy, may be disposed between the various layers. Another brazing process is controlled atmosphere brazing ("CAB") which is carried out in a dry oxygen-limited atmosphere, preferably using an inert environment, for example, nitrogen or argon can be used. To facilitate brazing, a non-corrosive brazing flux, e.g., a fluoride based flux as is well-known in the art, is applied prior to brazing on the pieces to be joined. This brazing flux removes or disturbs during the brazing operation the oxide layer to allow the molten filler to come into contact with bare metal to form the joint. The aluminium alloys used for CAB should be minimized in Mg because Mg can inhibit the brazing flux action. In complex shaped assemblies, the application of the non-corrosive brazing flux prior to brazing at the interior of the assemblies is often considered problematic.

Yet another brazing process is CAB without using a brazing flux, and this process is in particular being used for joining by means of brazing of surfaces inside a heat exchanger which are very difficult to flux and on an industrial scale is more cost effective than a vacuum brazing operation, as vacuum brazing is a batch process and requires considerable capital equipment costs.

There is a need for further improved brazing sheet materials and brazing processes in which at least the interior side of an assembly does not have to be provided with a non-corrosive brazing flux. DESCRIPTION OF THE INVENTION

As will be appreciated herein below, except as otherwise indicated, aluminium alloy designations and temper designations refer to the Aluminium Association designations in Aluminium Standards and Data and the Registration Records, as published by the Aluminium Association in 2016 and well known to the person skilled in the art.

For any description of alloy compositions or preferred alloy compositions, all references to percentages are by weight percent unless otherwise indicated. The term "up to" and "up to about", as employed herein, explicitly includes, but is not limited to, the possibility of zero weight-percent of the particular alloying component to which it refers. For example, up to 0.3% Cu may include an alloy having no Cu, and thus, there may be an absence of such element. And for the purpose of this invention, and as used hereinafter, the term "controlled atmosphere brazing" or "CAB" refers to a brazing process which utilizes an inert atmosphere, for example nitrogen or argon, in the brazing of the various alloy articles, and is distinct from vacuum brazing in particular in that with CAB the brazing atmosphere in the furnace during the brazing operation is at about atmospheric pressure, although a slight under-pressure (for example working at a pressure of 0.1 bar or more) or a slight over-pressure can be used to facilitate the control of the inert atmosphere and to prevent an influx of oxygen into the brazing furnace. "Core" means an aluminium alloy which is the structural support for the aluminium alloy used as the filler. "Filler" means an aluminium-silicon alloy which is used to braze the core or other aluminium articles. "Fillet" means a concave joint between two surfaces.

It is an object of the invention to provide an aluminium alloy brazing sheet ma- terial that can be applied in a CAB process without applying a non-corrosive brazing flux.

This and other objects and further advantages are met or exceeded by the present invention providing an aluminium alloy brazing sheet product comprising a covering aluminium material layer comprising 0.5% to 5% Zn, an aluminium core material layer, and an Al-Si alloy brazing material layer as an intermediate material interposed between said covering aluminium material layer and said aluminium core material layer, wherein said aluminium core material layer comprising of an aluminium alloy having a solidus temperature higher than the liquidus temperature of said Al-Si alloy brazing material layer, and wherein said Al-Si alloy brazing material layer contains from 0.01 % to 1 % Mg.

In an embodiment, the covering aluminium material layer is a thin covering material layer which is Mg-free, and the Al-Si alloy brazing material layer as an intermediate material is interposed between said thin covering material layer and said core material layer, and wherein said thin covering material layer and said core material layer comprised of aluminium alloys having a solidus temperature higher than a liquidus temperature of said Al-Si alloy brazing material so that the brazing material interacts with said covering material layer when the brazing material is molten in a brazing operation.

In accordance with the invention, it has been found that a brazing sheet product having a multi-layered structure having a covering aluminium material layer containing a purposive addition of Zn onto an Al-Si brazing material layer can be applied very successfully in a flux-free CAB operation. As the thickness of the covering layer with respect to the Al-Si alloy brazing material layer is preferably relatively small, the total amount of Zn in the fillet formed is still low and has no adverse effect on brazing and the performance of the brazed component. The presence of a small amount of Zn in this layer design may even contribute in providing sacrificial protection to the core alloy by enhancing corrosion resistance.

In an embodiment of the brazing sheet product, the covering aluminium material layer or top layer contains at least 0.7% Zn. In an embodiment of the brazing sheet product, the top layer contains at most 3.0% Zn, and preferably at most 2.5% Zn.

In patent document EP 1 306 207 B1 , it is reported that in order to achieve successful CAB brazing without the use of a brazing flux material, it is required that both the top layer and the aluminium core material layer should have a solidus tem- perature higher than the liquidus temperature of the intermediate brazing material layer. In this way, the molten brazing material during a subsequent brazing operation at a temperature between the liquidus temperature and the solidus temperature is to cause the Al-Si alloy brazing material layer to melt down while keeping the thin covering material layer solid to prevent oxidation of the brazing material being melted, and then cause the Al-Si alloy brazing material to, due to volumetric expansion, seep through segregation portions of the thin covering material layer onto a surface of the thin covering material layer and spread over the surface of the thin covering material to form an emerging surface resulting in a brazed joint. However, in EP-1306207-B1 there is no disclosure about the purposive addition of Zn to the top layer to facilitate the fluxless CAB operation.

In the brazing sheet material according to the invention, the core material layer is made for an aluminium alloy. The core alloys are preferably from the 2xxx-, 3χχχ-, 5χχχ-, or 6xxx-series aluminium alloys, in particular, from an 3xxx- or 6xxx- series aluminium alloys, such as AA3003, AA3103, AA3005, AA3105, AA6060, AA6063 or AA6951 -type alloy, or modifications thereof.

The Al-Si alloy brazing material layer is preferably made from an Al-Si alloy having 5% to 15% of Si and a purposive addition of Mg in a range of 0.01 % to 1 % to facilitate CAB brazing in the absence of a flux material. Preferably, there is at least 0.02% Mg present, more preferably at least about 0.05%, and more preferably at least about 0.09%. At most, the Mg content is 1 .0% and preferably at most about 0.25%.

In an embodiment, the Al-Si alloy brazing material layer contains further a purposive addition of Zn in a range of about 0.05% to 2%.

In an embodiment of the invention, the Al-Si brazing filler material layer has the following composition, consisting of,

Si 5% to 15% , preferably 6% to 14% ,

Mg 0.01 % to 1 %, preferably 0.05% to 1 .0%,

Fe up to 0.8%,

Cu up to 0.3%,

Mn up to 0.8%, preferably up to 0.2%,

Zn up to 2%,

Ti up to 0.3%,

balance aluminium, and unavoidable impurities each <0.05%, total <0.2%. In an embodiment, the Al-Si alloy brazing material layer further contains one or more wetting elements, or elements modifying the surface tension of a molten Al- Si filler material. Preferably, the elements are selected from the group comprising Bi, Y, Pb, Li, Na, Sb, Sr, and Th, and wherein the total amount of the wetting elements) is in a range of about 0.01 % to 0.8%. In a preferred embodiment, the upper- limit for the total amount of wetting element(s) is 0.5%.

In a preferred embodiment, the element Bi is selected from the defined group of wetting elements and is in a range of about 0.01 % to 0.8%, and preferably in a range of about 0.01 % to 0.5%, as being the most efficient wetting element for this purpose in this alloy system during a brazing operation. The brazing sheet product according to the invention has a typical thickness at final gauge in the range of about 0.1 mm to 10 mm, a preferably in a range of about 0.1 mm to 5 mm.

In an embodiment, the thin covering material layer has a thickness which is about 0.1 % to 10% of the entire thickness of the aluminium alloy brazing sheet, and the Al-Si alloy brazing material layer has a thickness which is about 3% to 30%, preferably about 4% to 20%, of the entire thickness of the aluminium alloy brazing sheet.

Further, in a preferred embodiment, the thickness ratio of the Al-Si alloy braz- ing material layer and the thin covering material layer is 3 or more to 1 , preferably 4 or more to 1 , for example the thickness ratio is 3 to 1 , or 3.5 to 1 , or 4 to 1 .

In an embodiment, the covering material layer is free of wetting elements or elements modifying the surface tension of a molten Al-Si filler material, selected from the group of Ag, Be, Bi, Ce, La, Li, Na, Pb, Se, Sb, Sr, Th, and Y. With "free" is meant that no purposeful addition of Ag, Be, Bi, Ce, La, Li, Na, Pb, Se, Sb, Sr, Th, or Y is made to the chemical composition but that due to impurities and/or leaking from contact with manufacturing equipment, trace quantities of may nevertheless find their way into the covering material layer. In practice, this means that the amount present, if present, is up to about 0.005%, typically less than about 0.001 %.

The covering material layer is preferably free from Mg, meaning that the level is below 0.05%, and preferably below about 0.03%, and more preferably below about 0.01 %. With "free" is meant that no purposeful addition of Mg is made to the chemical composition but that due to impurities and/or leaking from contact with manufacturing equipment, trace quantities of may nevertheless find their way into the covering material layer.

In an embodiment, the thin covering material layer is a Mg-free aluminium alloy comprising,

Fe 0 to 0.6%,

Si 0 to 4%, preferably 0 to 2%, more preferably 0 to 1 %,

Mn 0 to 1 .0%, preferably 0 to 0.4%,

Cu 0 to 0.5%, preferably 0 to 0.15%, more preferably 0 to 0.05%,

Zn 0.5% to 5%, preferably 0.7% to 3.0%, Ti 0 to 0.1 %,

inevitable impurities, each <0.05%, total <0.15%,

balance aluminium, and with preferred narrower compositional ranges as herein described and claimed.

In an embodiment, the thin covering material layer is a Mg-free aluminium alloy consisting of,

Fe 0 to 0.6%,

Si 0 to 4%, preferably 0 to 2%, more preferably 0 to 1 %,

Mn 0 to 1 .0%, preferably 0 to 0.4%,

Cu 0 to 0.5%, preferably 0 to 0.15%, more preferably 0 to 0.05%, Zn 0.5% to 5%, preferably 0.7% to 3.0%,

Ti 0 to 0.1 %,

other elements and inevitable impurities, each <0.05%, total <0.15%, balance aluminium, and with preferred narrower compositional ranges as herein described and claimed.

In another embodiment, the thin covering material layer is a Mg-free aluminium alloy, and next to the purposive addition of Zn having a composition within the range of AA1000-series aluminium alloys, and preferably an aluminium alloy selected from the group comprising AA1050, AA1070, AA1 100, AA1 145, and AA1230.

In a further aspect of the invention, there is provided an article comprising at least two formed members joint by brazing, for example a heat-exchanger, incorporating at least the aluminium alloy brazing product according to this invention as one of the formed members. The aluminium alloy brazing sheet product can be used in all known automotive heat exchanger types, e.g. powertrain cooling and HVAC designs. A typical example of a heat-exchanger benefiting for the aluminium alloy brazing material according to this invention is an oil cooler, and whereby ideally at least the covering aluminium material layer and Al-Si alloy brazing material layer joints a hollow formed in the article. Another typical example is a folded tube, its configurations being well known to the skilled person, in which there is an inner surface which cannot be fluxed whereas on the outer surface fins should be joined to the tube. In another aspect of the invention, there is provided a method of manufacturing an assembly of brazed components, comprising the steps of:

(a) providing or forming the components of which at least one is made from an aluminium alloy brazing sheet product as set out above or claimed;

(b) assembling the components into an assembly; and preferably one side of the brazing sheet product of the invention having the covering material layer is being kept inside the assembly forming the brazing sheet to constitute a structure, preferably a hollow structure;

(c) brazing the assembly without applying brazing flux in an inert gas atmosphere at a brazing temperature, typically at a temperature in a range of about 540°C to 615°C, for example at about 590°C or at about 600°C, for a period long enough for melting and spreading of the aluminium brazing filler material, for example a dwell time of about 1 to 10 minutes, preferably 1 to 6 minutes, typically at around about 2 or 4 minutes, to form a fillet between the filler material and at least one other component; and wherein the oxygen content of the dry inert gas atmosphere is controlled to a level as low as possible, preferably below 200 ppm, and more preferably below 100 ppm, and more preferably below 40 ppm; and

(d) cooling of the brazed assembly, typically to below 100°C; e.g. to ambient temperature.

Ideally, when assembling the components into an assembly suitable for joining by brazing, one side of the brazing sheet product of the invention having the relative thin covering material layer is being kept inside the assembly forming the brazing sheet to constitute a structure. While using the brazing sheet product according to this invention there is no requirement to apply a brazing flux in order to obtain a good joint following the brazing operation.

In a preferred embodiment the brazing inert gas atmosphere during the brazing operation should be dry, meaning that the dew point is less than minus 40°C, and more preferably of minus 45°C or even lower.

Another aspect of the invention relates to the use or method of use of the aluminium alloy brazing sheet product as herein described and claimed in a fluxless CAB operation as herein described and claimed, and preferably wherein one side of the brazing sheet product of the invention having the covering material layer is being kept inside the assembly forming the brazing sheet to constitute a structure, preferably a hollow structure, for manufacturing an assembly of brazed components, preferably a heat exchanger, more preferably an oil cooler.

The invention will now be illustrated with reference to non-limiting figures and embodiments according to the invention.

Typical arrangements of the aluminium alloy brazing sheet product 4 according to the invention are illustrated in Figs. 1 A, 1 B, and 1 C.

The covering aluminium material layer 2 and the intermediate Al-Si alloy brazing material layer 1 can be applied on both sides of or on one side only of the core material layer 3 and wherein the covering material 2 forms the outer layer of the multi-layered brazing sheet product. When both sides are clad, the brazing sheet product has five layers including the core alloy layer as shown in Fig. 1 A. When one side is clad with the brazing material, the brazing sheet product has a three layer configuration as shown in Fig. 1 B.

In another embodiment, when one side is clad with the Al-Si alloy brazing material layer, on the other side of the core material layer an outerlayer 5 can be applied as shown in Fig. 1 C. The outerlayer or outerliner would generally be of an alloy tailored to provide high corrosion resistance or corrosion resistance combined with erosion resistance in the environment to which that face of the sheet is exposed. An example of a suitable outerliner would be an aluminum alloy having a purposive addition of Zn, such as for example an AA7072-series alloy.

In another embodiment (not shown), a further aluminium alloy layer can be interposed between the core material layer and the Al-Si alloy brazing clad material layer. For example, a further aluminium alloy layer may be applied for example to limit diffusion of alloying elements from the core layer to the Al-Si brazing layer or to further improve on the corrosion performance of the brazing sheet product. Exam- pies of a suitable further aluminium alloy layer include aluminium alloys of the 1 xxx-, 3xxx- or 5xxx-series alloys. In a further embodiment, the 1 xxx-series alloys may have a purposive addition of Mg in a range of 0.1 % to 1 .5%, and in another embodiment the 5xxx-series alloys may have 0.1 % to 1 .5% Mg.

Fig. 2 is an isometric view of a portion of a brazed heat exchanger assembly. As shown in Fig. 2, a brazed aluminium heat exchanger 12 in accordance with the present invention may include a plurality of fluid-carrying tubes 6 made from the brazing sheet material in accordance with this invention. The ends of the fluid-carrying tubes 6 are open to a header plate 8 and a tank 10 (one end of the fluid- carrying tubes 6, one header plate 8 and one tank 10 are shown in Fig. 2). Coolant is circulated from the tank 10, through the fluid-carrying tubes 6, and into another tank (not shown). As shown, a plurality of cooling fins 7 are disposed between the fluid-carrying tubes 6 in order to transfer heat away therefrom, thereby facilitating a heat exchange cooling the fluid therein.

Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made without departing from the spirit or scope of the invention as herein described.

Claims

An aluminium alloy brazing sheet product (4) comprising a covering aluminium material layer (2) comprising 0.5% to 5% Zn, an aluminium core material layer (3), and an Al-Si alloy brazing material layer (1 ) as an intermediate material interposed between said covering aluminium material layer (2) and said aluminium core material layer (3), wherein said aluminium core material layer (3) comprising of an aluminium alloy having a solidus temperature higher than the liquidus temperature of said Al-Si alloy brazing material layer (1 ), and wherein said Al-Si alloy brazing material layer (1 ) contains from 0.01 % to 1 % Mg.

An aluminium alloy brazing sheet product according to claim 1 , wherein the covering aluminium material layer (2) is a thin covering material layer which is Mg free, and the Al-Si alloy brazing material layer (1 ) as an intermediate material is interposed between said covering material layer (2) and said core material layer (3), and wherein said covering material layer (2) and said core material layer (3) comprised of aluminium alloys having a solidus temperature higher than a liquidus temperature of said Al-Si alloy brazing material so that the molten brazing material seeps onto a surface of said covering material layer when said brazing material is molten in a brazing operation.

The aluminium alloy brazing sheet product according to claim 1 or 2, wherein said covering material layer (2) has a thickness which is 0.1 % to 10% of the entire thickness of said aluminium alloy brazing sheet product, and said Al- Si alloy brazing material layer (1 ) has a thickness which is 3% to 30% of the entire thickness of said aluminium alloy brazing sheet product.

The aluminium alloy brazing sheet product according to any one of claims 1 to 3, wherein the thickness ratio between the Al-Si alloy brazing material layer (1 ) and the covering material layer (2) is 3 or more to 1 , and preferably 4 or more to 1 . The aluminium alloy brazing sheet product according to any one of claims 1 to 4, wherein the covering material layer (2) has Mg below 0.05%, preferably below 0.03%, more preferably below 0.01 %, and is more preferably Mg-free.

The aluminium alloy brazing sheet product according to any one of claims 1 to 5, wherein the covering aluminium layer (2) comprises:

Fe 0 to 0.6%,

Si 0 to 4%, preferably 0 to 2%, more preferably 0 to 1 %, Mn 0 to 1 .0%,

Cu 0 to 0.5%,

Zn 0.5% to 5%,

Ti 0 to 0.1 %,

impurities, each <0.05% total <0.15%, balance aluminium.

The aluminium alloy brazing sheet product according to any one of claiml to 6, wherein the covering aluminium alloy layer (2) is an Mg-free aluminium alloy having a composition within the range of an 1000-series aluminium alloy.

The aluminium alloy brazing sheet product according to any one of claims 1 to 7, wherein the covering aluminium alloy layer (2) has a Zn-content of at least 0.7%, and preferably at most 3.0%.

The aluminium alloy brazing sheet product according to any one of claims 1 to 8, wherein the Al-Si alloy brazing material layer (1 ) consists of,

Si 5% to 15%,

Mg 0.01 % to 1 %,

Fe up to 0.8%,

Cu up to 0.3%,

Mn up to 0.8%,

Zn up to 2%, Ti up to 0.3%,

balance aluminium and unavoidable impurities.

10. The aluminium alloy brazing sheet product according to any one of claims 1 to 9, wherein the Al-Si alloy brazing material layer (1 ) further contains one or more wetting elements selected from the group consisting of Bi, Y, Pb, Li, Na, Sb, Sr, and Th, and wherein the total amount of the wetting element(s) is in a range of 0.01 % to 0.8%.

1 1 . The aluminium alloy brazing sheet product according to any one of claims 1 to 10, wherein the Al-Si alloy brazing material layer (1 ) has a Mg content in the range of 0.02% to 1 .0%, and preferably in the range of 0.05% to 1 .0%, and more preferably in the range of 0.09% to 0.25%.

12. A method of manufacturing an assembly of brazed components, comprising the steps of:

i. providing the components of which at least one is made from an aluminium alloy brazing sheet product according to any one of claims 1 to 1 1 ;

ii assembling the components into an assembly;

iii. brazing the assembly without applying flux in an inert gas atmosphere at a brazing temperature for a period long enough for melting and spreading of the filler material;

iv. cooling the brazed assembly.

13. Use of an aluminium brazing sheet product according to any one of claims 1 to 1 1 in manufacturing an assembly of brazed components in a flux-free controlled atmosphere brazing operation.

14. A brazed assembly incorporating an aluminium alloy brazing sheet according to any one claims 1 to 1 1 .

15. A brazed assembly according to claim 14, wherein the brazed assembly is an automotive heat exchanger.

16. A brazed assembly according to claim 14, wherein the brazed assembly is an oil cooler or a folded tube.