EP3423607A1

EP3423607A1 - Rolled aluminium alloy for heat exchangers

Info

Publication number: EP3423607A1
Application number: EP17705918.5A
Authority: EP
Inventors: Aleksandar Lozanov DAVIDKOV; Henricus Matheus Van Der Donk
Original assignee: Aleris Rolled Products Germany GmbH
Current assignee: Novelis Koblenz GmbH
Priority date: 2016-02-29
Filing date: 2017-02-23
Publication date: 2019-01-09
Anticipated expiration: 2037-02-23
Also published as: CN109072357A; EP3423607B1; US20210033358A1; CN109072357B; WO2017148788A1

Abstract

The invention relates to a heat exchanger incorporating at least one component made from a rolled 6xxx-series aluminium alloy having a composition, in wt.%, of Si 0.2% to 1.3%, Mg 0.3% to 1.3%, Cu up to 0.80%, Fe 0.05% to 1.0%, Mn 0.05% to 0.70%, optionally one or two elements selected from the group 0.05-0.35% Zr and 0.04-0.35% Cr, Zn up to 0.25%, Ti up to 0.25%, balance unavoidable impurities and aluminium, and wherein the Fe/Mn ratio is <1.90.

Description

HEAT EXCHANGER INCORPORATING A ROLLED ALUMINUM ALLOY

FIELD OF THE INVENTION

The invention relates to a brazed heat exchanger comprising various components and at least one component being made from the rolled 6xxx-series aluminium alloy product according to this invention. The invention relates further to the use of the rolled aluminium alloy in a heat exchanger.

BACKGROUND TO THE INVENTION

Heat exchangers and other similar equipment, such as condensers, evaporators and the like for use in car coolers, air conditioning systems, industrial cooling systems, etc. usually comprise a number of heat exchange tubes arranged in parallel between two headers, each tube joined at either end to one of the headers. Corrugated fins are disposed in an airflow clearance between adjacent heat exchange tubes and are brazed to the respective tubes. These various components are commonly joined to each other 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 an aluminium alloy of the 3xxx-series, having on at least one surface of the core sheet an aluminium clad layer (also known as an aluminium cladding layer). The aluminium clad layer is commonly made of a 4xxx-series alloy comprising silicon in an amount in the range of 4% to 20%, and preferably in the range of about 6% to 14%. 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, cladding spray-forming or semi-continuous or continuous casting processes. These aluminium clad layers have a liquidus temperature typically in the range of about 540°C to 615°C.

Although commercially sold brazing sheet products have predominantly a core alloy based on a 3xxx-series aluminium alloys, there are commercially available brazing sheet products having a heat-treatable 6xxx-series aluminium alloy as core alloy. These 6xxx-series alloys can be used also base plate of a heat exchanger or for manufacturing headers or side plates of a heat exchanger. Within the 6xxx- series alloys the alloys AA6101 , AA6151 , AA6951 , AA6060, AA6061 , and AA6063 can be found. A list of the key alloying elements of these alloys is given in Table 1 .

Table 1. Alloy composition (in wt.%) of several prior art rolled aluminium alloys used in heat exchangers and as registered with the Aluminium Association.

Alloy Element

Mg Si Fe Cu Mn Cr

AA6101 0.35-0.8 0.30- < 0.50 < 0.10 < 0.03 < 0.03

0.70

AA6151 0.45-0.8 0.6-1 .2 < 1 .0 < 0.35 < 0.20 0.15- 0.35

AA6951 0.40-0.8 0.20- < 0.8 0.15- < 0.10

0.50 0.40

AA6060 0.35-0.6 0.30-0.6 0.10- < 0.10 < 0.10 <0.05

0.30

AA6061 0.8-1 .2 0.40-0.8 < 0.7 0.15- < 0.15 0.04- 0.40 0.35

AA6063 0.45-0.9 0.20-0.6 < 0.35 < 0.10 < 0.10 < 0.10 For each alloy the balance is made by Zn as an impurity (commonly <0.25% or lower) and Ti (commonly <0.15% or lower), unavoidable impurities and the remainder is aluminium.

There is a need for improved rolled aluminium alloy products based on the 6xxx-series aluminium alloys for use in heat exchangers.

DESCRIPTION OF THE INVENTION

As will be appreciated herein, 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 2015 and are well known to the person skilled in the art. The temper designations are laid down in European standard EN515.

For any description of alloy compositions or preferred alloy compositions, all references to percentages are by weight percent unless otherwise indicated.

As used herein, the term "about" when used to describe a compositional range or amount of an alloying addition means that the actual amount of the alloying addition may vary from the nominal intended amount due to factors such as standard processing variations as understood by those skilled in the art.

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% Ti may include an alloy having no Ti.

It is an object of the invention to provide a heat exchanger incorporating at least one component made from an improved rolled 6xxx-series aluminium alloy.

These and other objects and further advantages are met or exceeded by the present invention providing a brazed heat exchanger incorporating at least one component made from a rolled 6xxx-series aluminium alloy having a composition, and wherein the rolled 6xxx-series aluminium alloy has a composition of: Si 0.2% to 1 .3%, Mg 0.3% to 1 .3%, Cu up to 0.80%, Fe 0.05% to 1 .0%, Mn 0.05% to 0.70%, optionally one or two elements selected from the group of 0.05-0.35% Zr and 0.04- 0.35% Cr, Zn up to 0.25%, Ti up to 0.25%, balance unavoidable impurities and aluminium, and wherein the Fe/Mn ratio is <1 .90.

In accordance with the invention it has been found that the rolled 6xxx-series aluminium alloy forms one of the components of a heat exchanger device and the rolled aluminium alloy used provides a good balance in post-braze mechanical properties and enhanced corrosion resistance, in particular after long term exposure at elevated temperatures, for example for 1 ,000 hours at 150°C, reflecting long term use of such a heat exchanger device. This would also allow some down-gauging of the heat exchanger component made from this 6xxx-series alloy.

The purposive combined addition of Mg and Si strengthens the aluminium alloy due to precipitation hardening of elemental Si and Mg2Si formed under the co- presence of Mg. In order to provide a sufficient post-braze strength level in the core sheet product the Si content should be at least 0.20%, and preferably at least 0.25%. A preferred upper-limit for the Si content is about 0.8%, and more preferably about 0.60%, and more preferably about 0.55%. The presence of Si enhances also the formability.

Substantially for the same reason as for the Si content, the Mg content should be at least 0.3%, and preferably at least about 0.35%, and more preferably at least 0.40% to provide sufficient strength to the rolled product. A preferred upper-limit for the Mg content is about 0.9%, and more preferably about 0.8%.

Fe is not a desired component of the aluminium alloy, but its presence is normally unavoidable. The Fe-content should not exceed 1 .0%, and a preferred upper- limit is about 0.8%, and more preferably about 0.50%. A preferred range is 0.05% to about 0.40%, and more preferably from about 0.10% to about 0.40%, because alloys containing less Fe are more expensive.

The presence of substantial amounts of Fe in the aluminium alloy has an adverse effect on the post-braze corrosion resistance. However, it has been found that the purposive effect of Mn to the aluminium alloy may significantly improve the post- braze corrosion resistance, for example the resistance to intergranular corrosion (IGC), in particular after long term exposure at elevated temperature and it increases the post-braze strength via solid solution hardening. Where 6xxx-series aluminium alloy according to the prior art and used in heat exchangers may have a presence of some Mn, it is referred to only by an upper-limit and thereby clearly suggesting that it is a tolerable impurity and the skilled person is expected to work at the lower-end of any disclosed Mn-range. In the aluminium alloy used according to this invention at least 0.05% Mn must be present. Preferably at least 0.08% Mn is present, and more preferably >0.10% Mn. A preferred upper-limit is about 0.50%, and more preferably about 0.40%. However, it is an important aspect of the invention that the Fe/Mn ratio is being controlled and the Fe/Mn-ratio should not exceed 1 .90, and preferably does not exceed 1 .80, and more preferably does not exceed 1 .75. A preferred lower-limit for the Fe-Mn ratio is about 0.7.

Cu may increase the post-braze strength of the aluminium alloy, but its presence should not exceed 0.80%. It is preferred that the Cu-level does not exceed about 0.4%. Cu levels above about 0.4% may rise to a reduced post-braze corrosion resistance of products incorporating the aluminium alloy according to the invention.

Ti may be present up to about 0.25% to act as a grain refining additive during the casting of an ingot of the aluminium alloy of the invention. Additional Ti may be added, for example due to their presence in scrap material, in order to increase the strength of the core alloy by solubility hardening. The total amount of Ti present in the alloy should preferably not exceed about 0.20%, but preferably is less than about 0.12%. A preferred lower limit for the Ti addition is about 0.01 %. Ti can be added as a sole element or with either boron or carbon as known in the art serving as a casting aid, for grain size control.

The Zn content in the aluminium alloy is present as a tolerable impurity element of less than about 0.25%, and preferably should be present at the lower-end of this range, e.g. less than about 0.15%, and more preferably less than about 0.10%, to maintain corrosion resistance at desired levels. To the aluminium alloy one or two dispersoid forming elements selected from the group consisting of about 0.05% to about 0.35% Zr and about 0.04% to about 0.35% Cr can be added to further improve the strength of the aluminium alloy product in the post-braze condition.

A more preferred Zr level is in the range of about 0.05% to about 0.20%, and more preferably in a range of about 0.06% to about 0.15%.

A more preferred Cr level is in the range of about 0.05% to about 0.20%, and more preferably in a range of about 0.06% to about 0.25%.

Preferably, if added to the aluminium, the total combined amount of all the dispersoid forming alloying elements Zr and Cr does not exceed about 0.35% to avoid the formation of coarse constituent particles in particular when combined with a relative high Fe content in combination with the purposive addition of Mn. Coarse constituent particles may have an adverse effect on formability and they may hinder further down-gauging of the product form and they can have an adverse effect on the corrosion resistance.

In an embodiment of the aluminium alloy it has no purposive addition of vanadium such that, if present, it is at a level of less than about 0.05%, and more preferably less than about 0.03%, such that the aluminium alloy is substantially free from V. With "substantially free" or "essentially free" is meant that no purposeful addition was made to the chemical composition but that due to impurities and/or leaking from contact with manufacturing equipment, trace quantities of V may nevertheless find their way into the alloy product. For example, less than about 0.02% is an example of a trace quantity. The aluminium alloy may have 0% V.

The aluminium alloy may contain normal and inevitable impurities, typically each <0.05% and the total <0.2%, and the balance is made by aluminium.

In an embodiment of the invention the 6xxx-series core alloy has a composition consisting of, in wt.%: Si 0.2% to 1 .3%, Mg 0.3% to 1 .3%, Cu up to 0.80%, Fe 0.05% to 1 .0%, Mn 0.05% to 0.70%, optionally one or two elements selected from the group 0.05%-0.35% Zr and 0.04%-0.35% Cr, Zn up to 0.25%, Ti up to 0.25%, balance unavoidable impurities and aluminium, and wherein the Fe/Mn ratio is <1 .90, and with preferred narrower alloy compositions are herein described. In a preferred embodiment of the invention the rolled 6xxx-series aluminium alloy is employed as a bare or non-clad rolled product in the heat exchanger such that in use the outer-face of the aluminium alloy is exposed to the corrosive environment, in particular as a so-called base plate where the heat exchanger apparatus is brazed onto. In this embodiment the thickness of rolled 6xxx-series alloy is in a range of about 1 mm to 12 mm.

In another embodiment the rolled 6xxx-series aluminium alloy has a first side and a second side, and at least one clad layer applied on the first side or the second side. There can be provided a clad layer on both the first side and the second side. The at least one clad layer can be a 1 xxx-series, e.g. AA1050, or a 7xxx- series alloy to provide sacrificial protection of the 6xxx-series alloy. A suitable 7xxx- series alloy would have a Zn-content of up to about 3%, and would include an AA7072-series alloy.

The clad material could also be made from a brazing material and preferably made of a 4xxx-series aluminium alloy. Typical alloys within this series are AA4343, AA4045, AA4047, AA4004, AA4104, AA4147, or some near compositional variants thereof. The 4xxx-series alloy may further contain one or more selected from the group consisting of Zn, In, and Sn, in a concentration tailored to effect a desired electrochemical potential within and adjacent to a brazing joint.

In accordance with the invention the rolled 6xxx-series alloy can be in the form a brazing sheet material wherein the 6xxx-series alloy forms the core alloy material and at least one side is clad with a brazing material, preferably a 4xxx-series alloy. Preferably such a brazing sheet material would be used for manufacturing a brazed tube as one of the components of the heat exchanger.

In a further embodiment of the invention, the 6xxx-series core alloy and the clad brazing material, preferably a 4xxx-series, are separated by an interliner or an interlayer, such that the core is bonded to an interliner, and the interliner is, in turn, bonded to the 4xxx-series alloy. This structure minimizes localized corrosion, pro- motes good brazeability, reduces liquid film migration, and, by suitable selection of the interliner alloy, enhances corrosion resistance, such that the interliner alloy sac- rificially protects the underlying core alloy. An example of a suitable interliner would be an 1xxx- or 3xxx-series alloy, or a 1xxx- or 3xxx-series alloy with a purposive addition of Zn below about 3%, or a purposive addition of In below about 1 %.

In another embodiment of such a brazing sheet product there is proved a core alloy bonded on both sides to an interliner, and each interliner is, in turn, bonded to a 4xxx-series alloy.

In another embodiment of the brazing product there is provided an outerliner or waterside liner bonded on one side of the core alloy and a clad brazing material bonded to the other side of the core alloy. Optionally there may be provided an interliner between the 6xxx-series core alloy and the clad brazing material. The outer- liner would generally be of an alloy tailored to provide high corrosion resistance or even corrosion 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 aluminium alloy having a purposive addition of Zn up to about 3%, such as for example an AA7072-series alloy.

The thickness of the core layer (in percent compared to the total thickness of the brazing sheet product) of the brazing sheet is preferably in a range of about 60% to 90%, the thickness of the interliner or interlayer or outerliner or waterside liner (in percent compared to the total thickness of the brazing sheet product) is preferably in a range of about 5% to 25% and the thickness of the clad brazing layer is preferably (in percent compared to the total thickness of the brazing sheet) in a range of about 4% to 15%. The thickness of the 6xxx-series core alloy at final clad composite gauge can be as little as about 80 microns to as much as about 5 mm.

In an embodiment of the invention the one component made from the rolled 6xxx-series alloys, either as a clad-product or a non-clad product, forms a base plate, a header or a side support of a heat exchanger. In this embodiment the thickness of rolled 6xxx-series alloy is in a range of about 1 mm to 12 mm. In a preferred embodiment the one component made from the rolled 6xxx- series alloys, either as a clad-product or a bare or non-clad product, forms a base plate of a heat exchanger, more preferably of an oil cooler.

The rolled 6xxx-series aluminium product is preferably provided in a fully- annealed Ό" temper or an "F" temper or in an "H" temper, i.e. in an H1 or H2 temper. An H1 temper means that the alloy product is strain hardened. An H2 temper means that the alloy product is strain hardened and partially annealed. In some embodiments, the alloy part may be strain hardened in accordance with typical H1 X or H2X temper practices, where X is a whole number from 0 to 9, e.g. H12 or H24 temper.

The rolled aluminium alloy used in the heat exchanger according to this invention is being cast into rolling feedstock, for example by means of DC-casting or continuous strip casting, and thereafter preferably homogenized prior to being down gauged by means of rolling to final gauge, for example by hot rolling and optionally also by cold rolling. Ideally during the casting process of the rolling stock there is no or very little formation of β-AIFeSi particles due to the purposive addition of Mn and by maintaining the Fe/Mn to less than 1 .90. However, where the formation of β- AIFeSi can't be avoided a homogenization heat-treatment assists in converting any β-AIFeSi to the less harmful a-AIFeSi form, preferably below 10μηη long and with 90% below 5 μιτι. The purposive addition of Mn acts to accelerate the β- to a-AIFeSi transformation in particular during homogenization so that the resulting homogenized ingot results in an increased post-braze corrosion resistance when used as a core alloy for a brazing sheet product or when used as base plate, a header or a side support of a heat exchanger. The as-cast rolling ingot is also homogenized to bring favourably the soluble secondary magnesium-silicon phases into suitable form.

The homogenisation heat-treatment involves heating the ingot for at least about 2 hours, and more preferably at least about 6 hours. A preferred upper-limit for the homogenisation soaking time is about 48 hours, and more preferably about 24 hours. A longer homogenisation time is not disadvantageous, but is not required and only serves to raise the costs of production. Homogenisation is preferably performed at a temperature of 525°C or more using one or more homogenisation steps, more preferably at least one homogenisation step is performed at a temperature range of 540°C to 600°C. The heat-up rates that can be applied are those which are regular in the art. Preferably, the aluminium alloy is homogenised for at least about 6 hours and preferably less than about 20 hours at a temperature range of about 550°C to about 600°C.

The present invention also relates to the use or a method of use of the rolled 6xxx-series aluminium alloy as described herein, either as a bare product or having at least one clad layer on one of its sides, for use in a heat exchanger. Preferably the alloy forms a base plate, a header or a side support of said heat exchanger. In particular the heat exchanger is a radiator, an oil cooler, an inter cooler, a heater core, an evaporator, a charge air cooler, or a condenser or similar applications and assemblies which are produced by joining brazing sheets for forming a compact assembly, mainly for the purpose of exchanging heat. The rolled 6xxx-series aluminium alloy is particularly useful for high performance, light weight, automotive heat exchangers but could be used for other brazed applications including but not limited to refrigeration and HVAC.

The invention shall also be described with reference to the appended FIG. 1 showing a drawing of the construction of a stacked plate oil cooler in a partially exploded illustration.

FIG. 1 shows schematically an example of the construction of a stacked plate oil cooler 1 which is constructed from a multiplicity of stacking plates 2 and metal turbulence plates 3 (turbulence inserts) arranged between said stacking plates 2. The stacked plate oil cooler 1 is closed off by means of a base plate 4 and a cover plate 5. An intermediate metal plate 6 is inserted between the uppermost metal turbulence plate 3 and the cover plate 5. Connections for the oil and a liquid coolant are arranged in the relative thick base plate 4, but cannot be seen or are not illustrated in this FIG. 1 . In contrast, the cover plate 5 is closed; it has, in this embodi- ment, stamped impressions 10, 12. In this example the base plate 4 can be made of the rolled 6xxx-series aluminium alloy according to the invention providing a good balance in post-braze mechanical properties and enhanced corrosion resistance, in particular after long term exposure at elevated temperatures, for example for 1 ,000 hours at 150°C, reflecting long term use of such a heat exchanger device.

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

1 . A heat exchanger incorporating at least one component made from a rolled 6xxx-series aluminium alloy having a composition, in wt.%, of

Si 0.2% to 1 .3%,

Mg 0.3% to 1 .3%,

Cu up to 0.80%,

Fe 0.05% to 1 .0%,

Mn 0.05% to 0.70%,

optionally one or two elements selected from the group 0.05-0.35% Zr and 0.04-0.35% Cr,

Zn up to 0.25%,

Ti up to 0.25%,

balance unavoidable impurities and aluminium, and wherein the Fe/Mn ratio is <1 .90.

2. A heat exchanger according to claim 1 , wherein the rolled 6xxx-series aluminium alloy has a Fe-content of maximum 0.8%, and preferably of maximum 0.50%.

3. A heat exchanger according to any one of claims 1 to 2, wherein the rolled 6xxx-series aluminium alloy has a Mn-content of maximum 0.50%, and preferably of maximum 0.40%.

4. A heat exchanger according to any one of claims 1 to 3, wherein the rolled 6xxx-series aluminium alloy has a Si-content of maximum 0.80%, and preferably of maximum 0.60%.

5. A heat exchanger according to any one of claims 1 to 4, wherein the rolled 6xxx-series aluminium alloy has a Mg-content of at least 0.40%.

6. A heat exchanger according to any one of claims 1 to 5, wherein the rolled 6xxx-series aluminium alloy has a Mg-content of not more than 0.9%, and preferably of not more than 0.8%.

7. A heat exchanger according to any one of claims 1 to 6, wherein the rolled 6xxx-series aluminium alloy has a Cu-content of up to 0.4%.

8. A heat exchanger according to any one of claims 1 to 6, wherein the rolled 6xxx-series aluminium alloy has been homogenized.

9. A heat exchanger according to claim 8, wherein the 6xxx-series core alloy has been homogenized for up to 48 hours at a temperature in a range of 525°C to 600°C, preferably in a temperature range of 540°C to 600°C.

10. A heat exchanger according to any one of claims 1 to 9, wherein the rolled 6xxx-series aluminium alloy has a Fe/Mn ratio of <1 .80, and preferably <1 .75.

1 1 . A heat exchanger according to any one of claims 1 to 10, wherein the rolled 6xxx-series aluminium alloy has a first side and a second side, and at least one clad layer on the first side or the second side.

12. A heat exchanger according to claim 1 1 , wherein the at least one clad layer is made from an alloy selected from the group consisting of a 1 xxx, 4xxx, and 7xxx-series aluminium alloy.

13. A heat exchanger according to any one of claims 1 to 10, wherein the rolled 6xxx-series aluminium alloy is non-clad.

14. A heat exchanger according to any one of claims 1 to 13, wherein the at least one component made from the rolled 6xxx-series aluminium alloy forms a base plate, a header or a side support of the heat exchanger.

15. A heat exchanger according to claim 14, wherein the at least one component made from the rolled 6xxx-series aluminium alloy has a thickness in a range of 1 mm to 12 mm and forms a base plate, a header or a side support of the heat exchanger.

16. A heat exchanger according to any one of claims 1 to 15, wherein the at least one component made from the rolled 6xxx-series aluminium alloy is provided in a fully annealed O-temper.

17. A heat exchanger according to any one of claims 1 to 15, wherein the at least one component made from the rolled 6xxx-series aluminium alloy is provided in a H1 X-temper or H2X-temper.

18. A heat exchanger according to any one of claims 1 to 15, wherein the at least one component made from the rolled 6xxx-series aluminium alloy is provided in an F-temper.

19. A heat exchanger according to any one of claims 1 to 18, wherein the heat exchanger is an automotive heat exchanger.

20. A heat exchanger according to any one of claims 1 to 19, wherein the heat exchanger is a radiator, a condenser, an evaporator, an oil cooler, an inter cooler, a charge air cooler or a heater core.

21 . Use of a rolled aluminium alloy as defined in any one of claims 1 to 18 as a component in a heat exchanger, preferably as a base plate, a header or a side support in said heat exchanger.