Method of Manufacturing a Brazing Sheet Product

Abstract

The invention relates to a method of manufacturing a brazing sheet product having a core layer of a 3xxx-series aluminium alloy clad on one or both sides with a 4xxx-series aluminium alloy brazing layer, the method comprising the steps of: (i) casting a rolling ingot of the core layer of a 3xxx-series aluminium alloy having the following composition, in wt. %: Mn 0.5-1.8, Si≤1.5, Fe≤0.7, Cu≤1.5, Mg≤1.0, Cr≤0.25, Zr≤0.25, Ti≤0.25, Zn≤0.5, balance impurities and aluminium; (ii) hot rolling of the rolling ingot to a hot rolled sheet having thickness of 2.5-10 mm; (iii) cold rolling of the hot rolled sheet to a gauge of 0.1-4 mm, optionally with an intermediate annealing step during the cold rolling operation; (iv) soft annealing to recrystallize the microstructure of the aluminium sheet, preferably at a temperature in the range of 250° C.-450° C.; (v) further cold rolling of the soft annealed sheet with a cold rolling reduction in the range of 5% to <10% to a final cold rolling thickness; and (vi) recovery annealing at 200° C.-420° C. of the cold rolled aluminium sheet at final cold rolling thickness.

Claims

1. A method of manufacturing a brazing sheet product having a core layer of a 3xxx-series aluminium alloy clad on one or both sides with a 4xxx-series aluminium alloy brazing layer, the method comprising the steps of: (a) casting a rolling ingot of the core layer of a 3xxx-series aluminium alloy having the following composition, in wt. %: TABLE-US-00004 Mn 0.5 to 1.8, Si up to 1.5, Fe up to 0.7, Cu up to 1.5, Mg up to 1.0, Cr up to 0.25, Zr up to 0.25, Ti up to 0.25, Zn up to 0.5, other elements and impurities each <0.05, total <0.15; balance aluminium. (b) hot rolling of the rolling ingot to a hot rolled sheet having thickness of 2.5 to 10 mm; (c) cold rolling of the hot rolled sheet to a gauge of 0.1 to 4 mm; (d) soft annealing to recrystallize the microstructure of the aluminium sheet; (e) further cold rolling of the soft annealed sheet with a cold rolling reduction in the range of 5% to <10% to a final cold rolling thickness; and (f) recovery annealing of the cold rolled aluminium sheet at final cold rolling thickness, wherein the recovery annealing is performed at a temperature in the range of 200° C. to 420° C.

2. The method according to claim 1, wherein the recovery annealing during step (f) is performed at a temperature in the range of 200° C. to 400° C.

3. The method according to claim 1, wherein the recovery annealing during step (f) is to an elongation of more than 10% in the brazing sheet product.

4. The method according to claim 1, wherein an intermediate annealing step is performed during the cold rolling operation and wherein the intermediate annealing during the cold rolling operation of step (c) is at a temperature in the range of 200° C. to 450° C.

5. The method according to claim 1, the 3xxx-series aluminium alloy has a Mg-content in the range of up to 0.7%.

6. The method according to claim 1, wherein the final cold rolling thickness during step (e) is to a thickness in the range of 0.1 mm to 3 mm.

7. The method according to claim 1, wherein the 3xxx-series aluminium alloy has a Mn-content in the range of 0.6% to 1.5%.

8. The method according to claim 1, wherein the 3xxx-series aluminium alloy has a Si-content in the range of up to 0.9%.

9. The method according to claim 1, wherein the 3xxx-series aluminium alloy has a Cu-content in the range of up to 1.2%.

10. The method according to claim 1, wherein the 3xxx-series aluminium alloy has a Cu-content in the range of up to 0.25.

11. The method according to claim 1, wherein the 3xxx-series aluminium sheet is clad on one or both sides with a 4xxx-series aluminium alloy brazing layer with each brazing layer having a thickness of 4% to 20% of the total brazing sheet thickness.

12. The method according to claim 1, wherein the brazing sheet product having a core layer of a 3xxx-series aluminium alloy clad on one or both sides with a 4xxx-series aluminium alloy brazing layer is devoid of any intermediate aluminium alloy layer positioned between the core layer and the brazing layer.

13. Heat exchanger incorporating a tube or plate made from the aluminium sheet manufactured according to claim 1.

14. The heat exchanger according to claim 13, wherein the heat exchanger is a stacked plate heat exchanger.

15. Use of an aluminium alloy brazing sheet product having a 3xxx-series aluminium alloy core layer manufactured according to claim 1 in a heat exchanger.

16. The method of claim 1, wherein the soft annealing is performed at a temperature in the range of 250° C. to 450° C.

17. The method of claim 2, wherein the recovery annealing during step (f) is performed at a temperature in the range of 250° C. to 380° C.

18. The method of claim 3, wherein the recovery annealing during step (f) is to an elongation of more than 14%.

19. The method of claim 5, wherein the Mg-content is in the range of 0.1% to 0.7%.

20. The method of claim 7, wherein the Mn-content is in the range of 0.6% to 1.25%.

Description

[0031] 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.

[0032] 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 embodiment, stamped impressions 10, 12. In this example in particular the stacking plates 2 can be made of the brazing sheet products manufactured by the method according to the invention.

[0033] The invention will now be illustrated with reference to non-limiting examples according to the invention.

Example

[0034] On an industrial scale of manufacturing a 3xxx-series aluminium core alloy has been DC-cast with the following composition, in wt. %, 1.05% Mn, 0.45% Cu, 0.25% Mg, 0.20% Fe, 0.09% Ti, 0.06% Si, 0.1% Zn, balance aluminium and inevitable impurities.

[0035] As is regular in the art, via roll bonding the core alloy has been clad on both sides with a 4xxx-series brazing filler alloy layer having a composition, in wt. %, of 9.9% Si, 0.7% Mg, 0.2% Fe, 0.06% Zn, 0.07% Bi, 0.02% Cu, balance aluminium and inevitable impurities. Each filler alloy brazing layer has a 10% thickness of the total brazing sheet thickness.

[0036] The brazing sheet package has been hot rolled and cold rolled to 0.39 mm and soft annealed at 370° C. for 2 hours (Condition 1).

[0037] Next the soft annealed cold rolled brazing sheet product has been cold rolled by about 7.7% reduction to a final gauge of 0.36 mm (Condition 2) and subsequently recovery annealed at 370° C. for 3 hours (Condition 3).

[0038] Brazing sheet products of Condition 1, 2 and 3 were given a simulated “slight cold work” treatment, as in common in the art and known to the skilled person, by stretching of about 4% using a standard tensile testing equipment to simulate the deformation resulting from industrial processes such as stamping and roll forming to produce components of heat exchangers. The core penetration depths (LFM) of the 4% stretched brazing sheet products were measured using standard metallography on metallographic sections after utilizing a simulated inert gas atmosphere braze cycle by soaking for 3 minutes at 600° C.

[0039] The brazing sheet product in Condition 1 had a core penetration depth of about 40 micron, whereas in Condition 2 and Condition 3 the core penetration depth was about 23 micron.

[0040] For each condition, using the applicable industry standard DIN EN ISO 6892-1:2017-02, the elongation (A50) has been measured in the L-direction. As an average over three measurements:

[0041] Condition 1: 14.9%

[0042] Condition 2: 9.0%

[0043] Condition 3: 15.1%

And in Condition 2 in the L-direction the measured Rp0.2 was 148 MPa and the Rm was 156 MPa, and in Condition 3 the measured Rp0.2 was 84 MPa and the Rm was 152 MPa.

[0044] From these experiments it can be seen that in an O-temper condition the brazing sheet product has a very good formability when expressed in A50 elongation but in combination with a very poor resistance to LFM. This resistance to LFM can be significantly improved by applying a further cold rolling reduction in a range of 5% to <10%. However, this increased resistance to LFM is associated with a reduction in formability, low elongation and high Rp0.2. However, the combination of a cold rolling reduction in a range of 5% to <10% and a recovery final annealing offers a favourable increased resistance to LFM and a formability comparable or even better than O-temper material.

[0045] In a further series of testing on the same brazing sheet material a process has been applied closely related to Condition 3 but with a recovery annealing at a lower temperature of about 300° C. for about 3 hours. It has been found that for the same alloy combination the core penetration depth was further reduced to less than 17 micron, while having a similar formability performance.

[0046] This renders the brazing sheet products manufactured in accordance with the invention suitable for use in heat exchangers, in particular for manufacturing components for stacked plate heat exchangers.

[0047] The invention is not limited to the embodiments described before, and which may be varied widely within the scope of the invention as defined by the appending claims.