WO2007131727A1

WO2007131727A1 - Method of producing a clad aluminum alloy sheet for brazing purposes and sheet produced by said method

Info

Publication number: WO2007131727A1
Application number: PCT/EP2007/004206
Authority: WO
Inventors: Desikan Sampath; Klaus Vieregge; Job Anthonius Van Der Hoeven; Scott W. Haller
Original assignee: Aleris Aluminum Koblenz Gmbh
Priority date: 2006-05-15
Filing date: 2007-05-11
Publication date: 2007-11-22

Abstract

A method for producing clad aluminium alloy sheet for brazing purposes including: (a) casting core alloy ingot from a charge produced using an amount of brazing sheet scrap, the core alloy including, in wt.%: Fe 0.06-0.6%, Si 0.4-1.3%, Cu 0.1-1.2%, Mg ≤ 0.25%, Mn 0.5-1.5%, Zn ≤ 0.25%, Ti ≤ 0.2%, Cr 0.05-0.2%, Zr ≤ 0.2%, optionally Sn < 0.25%, V < 0.25%, In < 0.20%, other elements ≤0.05% each and ≤0.15% total, balance aluminum; (b) cladding the core alloy with Al-Si alloy on at least one side with a clad ratio of 3-25%; (c) preheating the cladded core alloy to 400 to 530 °C for 1 to 25 hours prior to hot rolling; (d) hot rolling; (e) cold rolling to final thickness. The amount of brazing sheet scrap is at least 25% in weight of the total metal added to prepare the charge. The sheet including chromium containing (AI, Fe, Mn) and (AI, Fe, Mn, Si) intermetallics.

Description

METHOD OF PRODUCING A CLAD ALUMINUM ALLOY SHEET FOR BRAZING PURPOSES AND SHEET PRODUCED BY SAID METHOD

FIELD OF THE INVENTION

The invention relates to a method for producing a clad aluminum alloy sheet for brazing purposes and a sheet produced by the method.

BACKGROUND OF THE INVENTION

Currently used high strength and high corrosion resistance long life aluminum brazing sheet products are typically characterised by low levels of iron (Fe) and silicon (Si) to produce tubes for transporting coolants or refrigerants in aluminum heat exchangers (tube stock). Brazing sheet typically comprises a core alloy and at least one cladding layer. Fe-levels in core alloys intended for tube stock applications are deliberately kept low in order to achieve a good corrosion resistance in the post-brazed condition. Consequently, the production of such tube stock materials demands the use of high grade primary aluminum that does not allow any significant re-use of aluminum brazing sheet scrap material.

During the production of brazing sheet, large quantities of brazing sheet scrap become available. This scrap contains significant levels of alloying elements, particularly silicon, copper (Cu) and iron. These levels of alloying elements severely limit the re-use of the scrap, particularly for producing new brazing sheet long life core alloys.

SUMMARY OF THE INVENTION

It is an object of this invention to provide high strength and high corrosion resistant aluminum brazing sheet materials allowing the use of significant amounts of brazing sheet scrap as charge material. These properties should be retained over a wide compositional range.

This object and other advantages are reached by providing a process for producing a clad aluminum alloy sheet for brazing purposes comprising the steps of: a. Casting a core alloy ingot from a charge, the charge being produced using an amount of brazing sheet scrap, the core alloy comprising, in wt.%:

Fe 0.06-0.60%,

Si 0.4-1.3%,

Cu 0.1-1.2%,

Mg < 0.25%,

Mn 0.5-1.5%,

Zn < 0.25%,

Ti < 0.2%,

Cr 0.05-0.2%,

Zr < 0.2%, optionally comprising Sn < 0.25%, V < 0.25%, In < 0.20%, other elements: 0.05% maximum each and 0.15% maximum total, balance aluminum; b. Cladding the core alloy with an Al-Si alloy on at least one side with a clad ratio of 3-25%; c. Preheating the cladded core alloy to a preheating temperature of between 400⁰C and 530⁰C for between 1 to 25 hours prior to hot rolling; d. Hot rolling; e. Cold rolling to a final thickness, wherein the amount of brazing sheet scrap is at least 25% in weight of the total metal added to prepare the charge, for producing an aluminum alloy sheet comprising chromium containing (AI₁Fe₁Mn) and (AI₁Fe₁Mn₁Si) intermetallics.

It should be noted that all compositional amounts and ranges are given in terms of weight percent. It should also be noted that the core alloy ingot may be a conventional ingot, or a continuously cast slab, thin cast slab or cast strip. The clad ratio is defined as the percentage of clad layer thickness of the total thickness of the entire brazing sheet comprising the core alloy and the clad layer or layers. By means of example, a core alloy of 9 mm with a clad layer on one side of 1 mm results in a clad ratio of 10%.

BRIEF DESCRIPTION OF THE DRAWING

Figs. 1a-1l show a number of configurations of brazing sheet which can be produced according to the invention.

Fig. 2 shows schematically and labels layers of Figs. 1a-1l.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a process for producing a clad aluminum alloy sheet for brazing purposes comprising the steps of: a. Casting a core alloy ingot from a charge, the charge being produced using an amount of brazing sheet scrap, the core alloy comprising, in wt.%:

Fe 0.06-0.60%,

Si 0.4-1.3%,

Cu 0.1-1.2%,

Mg ≤ 0.25%,

Mn 0.5-1.5%,

Zn ≤ 0.25%,

Ti ≤ 0.2%,

Cr 0.05-0.2%,

Zr ≤ 0.2%, optionally comprising Sn < 0.25%, V < 0.25%, In < 0.20%, other elements 0.05% maximum each and 0.15% maximum total, balance aluminum; b. Cladding the core alloy with an Al-Si alloy on at least one side with a clad ratio of 3-25%; c. Preheating the cladded core alloy to a preheating temperature of between 400⁰C and 530⁰C for between 1 to 25 hours prior to hot rolling; d. Hot rolling; e. Cold rolling to a final thickness, wherein the amount of brazing sheet scrap is at least 25% in weight of the total metal added to prepare the charge, for producing an aluminum alloy sheet comprising chromium containing (Al, Fe, Mn) and (Al, Fe, Mn, Si) intermetallics.

The Al-Si alloy clad on at least one side of the core alloy preferably has a Silicon content of 3 to 4%, such as for example AA4045, AA4343 or AA4145. The reasons for the limitations of the alloying elements of the aluminum alloy according to the present invention are described below.

Si is an important alloying element in the alloy according to this invention. The addition of Si results in an increased solution and precipitation hardening of the alloy. Above 1.3% it may result in the formation of detrimental low-melting eutectics and also in the formation of large intermetallic particles. A more suitable minimum Si content is 0.75%. In many aluminum alloys a Si-level at this medium range is regarded as detrimental. An advantage of this medium range Si-content is that the alloy has a tolerance for impurity elements, and allows this alloy to be composed from large amounts of scrap material. Preferably the sum of Si+Mn is in the range of 1.45-2.75%, and more preferably in the range of 1.5-2.75%, because this allows for a good compromise in desired properties of the alloy such as post-braze strength and corrosion resistance. In an embodiment, Si is between 0.4 and 0.7%.

Mn is also an important alloying element in the alloy according to this invention. A Mn-level between 0.5 and 1.5% proves to result in satisfactory properties over the entire range. A preferred lower limit for the Mn content is 0.55%. A preferred upper limit for the Mn content is 1.4%. More preferably the Mn should be in the range of 0.55 to 1.28%. This preferable range results in very consistent properties over the Mn-range. The addition of chromium and the use of scrap as charge material alters the composition of the intermetaϋics, thereby preventing the formation of large Fe-Mn intermetallics as a result of the high Mn content. The Mn level should not exceed 1.5%. However, above 1.2% Mn a successful casting requires judicious combination of casting parameters.

Mg increases the strength of the alloy significantly, but has a detrimental influence on controlled atmosphere brazeability because it tends to interact with the flux applied. For this reason the Mg content is restricted to a maximum of <0.25%.

Fe is present in all known aluminum alloys. An Fe-content between 0.06 and 0.60% proved to result in a suitable compromise of formability, corrosion performance and solidus temperature. With a too high Fe content among other things the formability of the material decreases and also the corrosion performance decreases. Also the solidus temperature may decrease below an acceptable level using too high an Fe content. A suitable minimum Fe-content is 0.20% in view of the higher post-braze strength. A suitable maximum Fe content is 0.55%, preferably 0.50%, particularly in view of the decreasing solidus temperature. A suitable Fe content is in the range of 0.25 to 0.48%, and allows for a good compromise in desired properties of the alloy such as post-braze strength and corrosion resistance, while the alloy can be manufactured without great difficulties using scrap material.

Cu is preferably included as a strengthening or hardening component. Above copper contents of 1.2%, successful casting of commercial size ingots can be affected due to hot cracking. A suitable maximum for the Cu content is up to 1.05%. A suitable minimum for the Cu content is 0.30%. Preferably the Cu- content is between 0.33 and 1.0% as a compromise in achieving post-braze strength, corrosion resistance and brazeability. In an embodiment of the invention the Cu-content is between 0.55 and 1.0 wt.%. With regard to the role of copper in corrosion resistance, the most recent work shows rather a favourable influence, while the copper remains in solid solution.

Zn addition must remain below 0.25% in order to avoid a too high susceptibility to generalised corrosion. A more preferred maximum is 0.10% to reduce the tendency to generalised corrosion even further.

Ti may be present up to 0.2% to act as a grain refining additive during the casting of an ingot of the alloy of the invention. Additional Ti may be sdded in order to improve corrosion resistance in the post-braze condition. The total amount of Ti present in the alloy should not exceed 0.2% to prevent formation of coarse intermetallics during casting process, but preferably is less than 0.15%.

Optionally, the element Indium in a range of up to 0.20% may be added to the alloy of the invention in order to reach a more electro-negative corrosion potential. Furthermore, it has been found in accordance with the invention that in the aluminum alloy according to the invention In is much more effective in reducing the corrosion potential of the alloy as compared to zinc additions. Typically 0.1% In is as effective as 2.5% Zn. When added as a deliberate alloying element a more preferred range for In is 0.01 to 0.10%. A suitable minimum In- addition is 0.06%.

Other components including Sn and V may optionally be used as alloying elements in the alloy according to the invention in a range up to 0.25%, preferably up to 0.15%. When used as an alloying element a suitable minimum amount of Sn or V is 0.06%. The total of these elements should not exceed 0.3%. Such element or elements may be present to reduce the corrosion potential of the alloy, and V has further the potential of increasing post-braze strength.

Zr in a range of up to 0.2% may optionally be used as alloying element to the alloy of this invention in order to further improve the strength of the alloy in the post-braze condition. Further, this element may be tolerated as an impurity element without affecting the properties of the alloy. In this case the Zr-content is less than 0.05 wt.%. A more suitable Zr addition is in the range of 0.05 to 0.20%, and more preferably in the range of 0.05 to 0.15%. In the latter case, it has been found to be beneficial to have a Cu content between 0.2 and 0.5%. In this embodiment part of the zirconium is replaced by copper and the strength in post- braze condition is maintained at a sufficiently high level.

The balance is made by aluminum and other elements, typically each up to 0.05% maximum, and in total 0.15% maximum.

According to the invention the Mg-content is up to 0.25%. Mg increases the strength of the alloy significantly, but it also has a detrimental influence on controlled atmosphere brazeability because it tends to interact with the flux applied. For this reason a more suitable maximum for the Mg content is 0.15%, and more preferably below 0.05%.

In an embodiment of the invention the process provides a clad aluminum alloy with a post-braze proof stress (Rp) of at least 45 MPa, a post-braze tensile strength (Rm) of at least 135 MPa and a post-braze SWAAT corrosion resistance according to ASTM G85 (part A3) of 24 hours. It should be noted that the post- braze SWAAT corrosion resistance should be the average of a plurality of samples, preferably three samples or more.

According to the invention the charge, used to produce the melt from which the core alloy is cast, comprises an amount of brazing sheet scrap of at least 25%. As a consequence, the levels of Fe, Si and Cu of the core alloy are significantly higher and more variable from cast to cast than those O₁ conventional tube-stock materials. This would normally lead to deterioration of the corrosion resistance and increase strength fluctuations in post-braze condition. However, the inventors have found that the combination of the use of brazing sheet scrap and a small but deliberate addition of chromium to the εlloy minimizes any post-braze strength fluctuations caused by the variations in Fe, Si and Cu levels and, at the same time, improves the corrosion resistance. This surprising effect of Cr is attributed to Cr being present as a parϊ of the (Al, Fe, Mn) and (Al, Fe, Mn, Si) intermetallics, instead of coarse intermetallics of AI₇Cr. These fine, chromium containing intermetallics are formed during ingot casing as a result of the use of large amounts of brazing sheet scrap and the subsequent thermal and mechanical processing steps to manufacture brazing sheet products. These fine chromium containing intermetallics are essential tc the product. According to this invention, Cr is also known to improve the strength of the alloy in the post-braze condition. The addition of at least 25% of brazing sheet scrap therefore results in good and consistent properties and in beneficial effects from an environmental and economical point of view. A Cr addition c^' between 0.05 and 0.20% provided the desired intermetsllics. Preferabiy, the deliberate addition of Cr-content is at least 0.06% so as to provide a higher Cr- content in the intermetallics.

The process according to the invention may comprise intermediate and final annealing processes if required. This will particularly be the case in the production of thinner gauges, especially in case multiple cold rolling reductions are required.

In an embodiment of the invention, the cast core alloy is homogenized, with a temperature between 500⁰C and 620⁰C for between 1 to 30 hours, preferably for a maximum of 25 hours. This homogenization is favourable to the ductility of the rolled strip and it is always carried out when the strip is used in the O state. It encourages coalescence of the dispersoϊds with the Mn which in turn facilitates ease of hot rolling the materials. In the absence of homogenization and with a work hardened and recovered strip, after brazing, for strips according to the invention, one obtains a microstructure with elongated grains, which imparts good brazeability to thinner gauge products.

In an embodiment of the invention the amount of brazing sheet scrap to produce the melt for the core alloy is at least 30%, preferably at least 35% and more preferably at least 40%. A suitable maximum amount is 75%. However, this maximum may be chosen even larger as long as the composition of the melt remains within the ranges as claimed.

In an embodiment of the invention the process comprises cladding the core alloy on both sides with the Al-Si alloy.

In an embodiment of the invention the process comprises cladding the core alloy on one side with the Al-Si alloy and cladding a non-brazing alloy liner on the other side. The Al-Si alloy optionally comprises up to 2.0% Zn. The non-brazing alloy liner may be an alloy of the AA7XXX-series such as AA7072, of the AAIXXX-series such as AA1145, of the AA3XXX series such as AA3005 or an alloy of the AA3XXX-series further comprising Zn in the range 0.5 - 5.0%, and optionally further comprising Mg in the range 0.5 to 3.0%.

Optionally the process according to the invention comprises providing the core alloy with an interliner with a clad ratio of 3-25%. The interlayer is positioned between the core alloy and the braze clad (also known as braze cladding) or waterside liner. The interliner should be selected so as not to influence the microstructure, particularly that of the Cr-containing phase, of the core alloy. The braze clad and the non-braze liner (if present) is clad on the core alloy comprising the interliner layer or layers. If two inteiiiners are clad onto the core alloy, the interliners on both sides of the core alloy may be different or identical in composition and/or thickness in the resulting clad aluminum alloy sheet for brazing. The sheet provided with one or more interliners, a braze clad and/or a non-braze liner may be provided with one or more additional layers on either side if circumstances so dictate. The clad aluminum alloy sheet according to the invention is therefore not limited to a five layer system (five, including the core layer), but may comprise 6 or more layers.

When the purpose of the clad aluminum alloy sheet is for producing parts requiring a high degree of forming, the sheet can be used in the annealed state (O state) by proceeding to a final annealing at a temperature between 250 and 425°C, preferably between 300 and 425°C, either continuously or in batches. This annealing leads to a microstructure with recrystallised grains. In other cases it is used in the work hardened temper, which leads to better mechanical strength, for example an H14 or H24 temper (according to Standard NF EN 515), the latter temper being obtained through a recovery annealing treatment between 200 and 300⁰C, thereby substantially avoiding recrystallisation.

According to a second aspect, the invention provides a clad aluminum alloy sheet product for brazing sheet comprising a core alloy and at least one Al-Si alloy cladding layer on at least one side of the core alloy with a clad ratio of 3- 25%, the core alloy comprising, in wt.%:

Fe 0.06-0.60%,

Si 0.4-1.3%,

Cu 0.1-1.2%,

Mg < 0.25%,

Mn 0.5-1.5%,

Zn < 0.25%,

Ti < 0.2%, Cr 0.05-0.2%, Zr < 0.2%, optionally comprising Sn < 0.25%, V < 0.25%, In < 0.20%, other elements 0.05% maximum each and 0.15% maximum total, balance aluminum, wherein the core alloy comprises (Al-Fe-Mn) and (Al-Fe-Mn-Si) intermetallics, the intermetallics comprising chromium as an integral part. Preferably the intermetallics in pre-braze condition are substantially in the size range of 20 to 4000 nm.

Preferential ranges for the respective alloying elements and the embodiments resulting therefrom have been discussed hereinabove and set forth in the examples and claims.

This core alloy is produced from a cast ingot, cast slab or cast strip which is produced using brazing sheet scrap material as charge material for the melt to cast the ingot, slab or strip and the fine, resulting in the formation of fine, chromium containing intermetallics. This provides the clad aluminum alloy with the good and consistent mechanical and corrosion properties. In an embodiment of the invention a clad aluminum alloy is provided with a post-braze proof stress (Rp) of at least 45MPa, a post-braze tensile strength (Rm) of at least 135 MPa and a post-braze SWAAT corrosion resistance against perforation of at least 24 hours. Again it should be noted that the post-braze SWAAT corrosion resistance should be the average of a plurality of samples, preferably three samples or more. Preferably these intermetallics are between 20 and 4000 nm in size, more preferably at most 1000 nm in size. A preferable range for the intermetallics is between 40 and 750 and more preferably between 80 and 200 nm. These fine, chromium containing intermetallics are formed during ingot casting as a result of the use of large amounts of brazing sheet scrap and the subsequent thermal and mechanical processing steps to manufacture brazing sheet products. The intermetallics are thus already present in the core alloy prior to brazing.

In an embodiment the Al-Si cladding alloy further comprises a Zn-content of at most 2.0%. In an embodiment of the invention a clad aluminum alloy sheet for brazing produced according to the process of the invention is provided with a final thickness after cold rolling of between 0.10 to 5.0 mm.

In an embodiment of the invention a clad aluminum alloy sheet for brazing for welded and brazed tube and tube-plate stock applications produced according to the process of the invention is provided, wherein the thickness of the sheet is between 0.15 to 0.8 mm.

In an embodiment of the invention a clad aluminum alloy sheet for brazing purposes for header and side support applications produced according to the process of the invention is provided wherein the thickness of the sheet is between 0.5 to 3.0 mm.

According to a third aspect the use of the clad aluminum alloy sheet for brazing produced according to the process of the invention is provided to produce a flux brazed heat exchanger (Nocolok™) or vacuum brazed aluminum heat exchanger units such as radiators, evaporators, condensers, charge air coolers, oil coolers and the like.

The invention is also embodied in a clad aluminum alloy sheet for brazing produced according to the process of the invention.

The invention will now be further explained by the following, non-limitative, Figs. 1a-1l and Fig. 2. Figs. 1a-1l illustrate a number of configurations of brazing sheet which can be produced according to the invention. Labelling of the layers on Figs. 1a-1l is not needed because the different layers on Figs. 1a-1l are indicated schematically to look the same as the corresponding layers in Fig. 2. Fig. 2 labels the individual layers as layers A, B, C and D which represent the following:

A: core alloy

B: Al-Si cladding layer

C: lnterliner

D: Waterside liner.

EXAMPLES The invention will now be further explained by the following, non-limitative, examples. The results for these examples are indicated in Tables 1 and 1A where the chemical composition of the core alloy and the configuration of different cladding systems are described.

Column 2 of Tables 1 and 1A indicates whether the brazing sheet is according to the invention ("I") or for comparison ("C"). The composition of the waterside liner and the interliner alloys (if applicable) is indicated in Table 3. The amount of scrap used to produce the core alloy as per column 3 of Table 1 is given in Table 2, 3^rd column.

It can be clearly seen from Table 2 that the comparative examples, where the amount of scrap used to produce the core alloy is below 10%, show an inferior performance in terms of the post-brazing properties. It is apparent that the use of the scrap in combination with the addition of the chromium results in superior properties in comparison to the comparative examples.

While particular embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes and modifications may be made thereto without departing from the invention in its broader aspects and as set forth in the following claims.

Claims

1. A process for producing a clad aluminum alloy sheet product for brazing purposes comprising the steps of: a. casting a core alloy ingot from a charge, the charge being produced using an amount of brazing sheet scrap, the core alloy comprising, in wt.%:

Fe 0.06-0.60%,

Si 0.4-1.3%,

Cu 0.1-1.2%,

Mg < 0.25%,

Mn 0.5-1.5%,

Zn < 0.25%,

Ti < 0.2%,

Cr 0.05-0.2%,

Zr < 0.2%, optionally comprising Sn < 0.25%, V < 0.25%, In < 0.20%, other elements 0.05% maximum each and 0.15% maximum total, balance aluminum; b. Cladding the core alloy with an Al-Si alloy on at least one side with a clad ratio of 3-25%; c. Preheating the cladded core alloy to a preheating temperature of between 400 ⁰C and 530 ⁰C for between 1 to 25 hours prior to hot rolling; d. Hot rolling; e. Cold rolling to a final thickness, wherein the amount of brazing sheet scrap is at least 25 % in weight of the total metal added to prepare the charge, for producing an aluminum alloy sheet comprising chromium containing (Al, Fe, Mn) and (Al, Fe, Mn, Si) intermetallics.

2. The process according to claim 1 , where the cast core alloy is homogenized with a temperature between 500⁰C and 620⁰C for between 1 to 25 hours.

3. The process according to claim 1 , wherein the amount of brazing sheet scrap is at least 30%, preferably least 35%.

4. The process according to any claim 1 , wherein the Mg is at most 0.15%.

5. The process according to claim 1 , wherein the Si is between 0.4 - 0.7%.

6. The process according to claim 1 , wherein the Cu is between 0.55 and 1.0%.

7. The process according to claim 1 , wherein the Zr is less than 0.05%.

8. The process according to claim 1 , wherein the Cu is between 0.2 - 0.5 weight % and the Zr is between 0.05 to 0.15 weight %.

9. The process according claim 1 , further comprising cladding the core alloy on one side with the Al-Si alloy and cladding a non-brazing alloy liner on the other side.

10. The process according claim 1 , further comprising cladding the core alloy on one side with the Al-Si alloy and cladding a non-brazing alloy liner on the other side selected from the group consisting of AA7072, AA1145, AA3005, or an Al-Mn alloy comprising Zn in the range 0.5 to 5.0 wt.%, said Al-Mn optionally comprising Mg in the range 0.5 to 3.0%.

11. A clad aluminum alloy sheet product for brazing purposes comprising a core alloy and at least one Al-Si alloy cladding layer on at least one side of the core alloy with a clad ratio of 3-25%, the core alloy comprising, in wt.%:

Fe: 0.06-0.60%,

Si: 0.4-1.3%,

Cu: 0.1-1.2%,

Mg: < 0.25%,

Mn: 0.5-1.5%,

Zn: < 0.25%,

Ti: < 0.2%,

Cr: 0.05-0.2%,

Zr: < 0.2%, optionally comprising Sn < 0.25%, V < 0.25%, In < 0.20%, other elements: 0.05% maximum each and 0.15% maximum total, balance aluminum, wherein the core alloy comprises (Al-Fe-Mn) and (Al-Fe-Mn-Si) intermetallics, the intermetallics comprising chromium as an integral part.

12. The clad sheet according to claim 11 , wherein the intermetallics in pre-braze condition are substantially in the size range of 20 to 4000 nm.

13. The clad sheet according to claim 11, wherein the post-braze tensile strength of the material is at least 135 MPa and the proof strength is at least 45 MPa.

14. The clad sheet according to claim 11, wherein the thickness of the sheet is between 0.10 to 5.0 mm.

15. The clad sheet produced for welded and brazed tube and tube-plate stock applications according to claim 11, wherein the thickness of the sheet is between 0.15 to 0.8mm.

16. The clad sheet produced for header and side support applications according to claim 11 , wherein the thickness of the sheet is between 0.5 to 3.0 mm.

17. The clad sheet produced according to claim 11, wherein the post-braze SWAAT corrosion resistance tested according to ASTM G85 (part 3) is at least 24 hours.

18. A method for producing a product selected from the group consisting of a flux brazed heat exchanger and a vacuum-brazed aluminum heat exchanger unit, wherein at least said first member comprises the sheet produced according to claim 1.

19. The method of Claim 18, wherein said vacuum-brazed aluminum heat exchanger unit is selected from the group consisting of radiators, evaporators, condensers, charge air coolers, and oil coolers, comprising brazing a first member to a second member.

20. A method for producing a product selected from the group consisting of a flux brazed heat exchanger and a vacuum-brazed aluminum heat exchanger unit, wherein at least said first member comprises the sheet produced according to claim 11.

21. The method of Claim 18, wherein said vacuum-brazed aluminum heat exchanger unit is selected from the group consisting of radiators, evaporators, condensers, charge air coolers, and oil coolers, comprising brazing a first member to a second member.