Brazing sheet

Abstract

The invention concerns a brazing sheet comprising a core layer (5) and a braze cladding, said core layer (5) being aluminium or an aluminium alloy, said braze cladding comprising (a) a flux composite layer (2), which flux composite layer comprises a matrix of aluminium or an aluminium alloy, said matrix containing flux particles; (b) at least one filler alloy layer (1) not containing flux particles; and, (c) an aluminium or aluminium alloy layer (3) not containing flux particles, said layer forming the outermost surface of at least one side of the brazing sheet, wherein the flux composite layer (a) is positioned between said filler alloy layer (b) and said aluminium or aluminium alloy layer (c). The invention further concerns a method for its manufacturing, a cladding plate, use of the brazing sheet and a brazed heat exchanger.

Claims

1. Brazing sheet comprising a core layer and a braze cladding, said core layer being aluminium or an aluminium alloy, said braze cladding comprising (a) a flux composite layer, which flux composite layer comprises a matrix of aluminium or an aluminium alloy, said matrix containing flux particles; (b) a filler alloy layer not containing flux particles; and (c) an aluminium or aluminium alloy layer not containing flux particles, said layer forming the outermost surface of at least one side of the brazing sheet, wherein the flux composite layer (a) is positioned between said filler alloy layer (b) and said aluminium or aluminium alloy layer (c), and wherein a liquidus temperature of the filler alloy layer is lower than a solidus temperature of the aluminium or aluminium alloy of the core layer.

2. Brazing sheet as claimed in claim 1, wherein the aluminium or aluminium alloy layer (c) forming the outermost surface of at least one side of the brazing sheet is a filler alloy layer.

3. Brazing sheet as claimed in claim 1, wherein the aluminium or aluminium alloy layer (c) forming the outermost surface of at least one side of the brazing sheet is a non-filler aluminium or aluminium alloy layer.

4. Brazing sheet as claimed in claim 1, wherein the at least one filler alloy layer is an aluminium alloy comprising from 2 to 15 wt % of Si.

5. Brazing sheet as claimed in claim 1, wherein the matrix in the flux composite layer is aluminium or an AA1XXX, AA2XXX, AA3XXX, AA4XXXX, AA7XXXX, or AA8XXX aluminium.

6. Brazing sheet as claimed in claim 5, wherein the matrix in the flux composite layer is a filler alloy.

7. Brazing sheet as claimed in claim 5, wherein the matrix in the flux composite layer is aluminium or a non-filler aluminium alloy.

8. Brazing sheet as claimed in claim 1, wherein the amount of Mg in the matrix of the flux composite layer is wt %.

9. Brazing sheet as claimed in claim 1, wherein the flux is at least one inorganic salt comprising F and at least one of Li, Na, K, Rb, Cs, Fr, Al, Zn or Sn.

10. Brazing sheet as claimed in claim 1, wherein content of flux in the flux composite layer is from 1 to 20 wt %.

11. A method for the manufacturing of a brazing sheet according to claim 1, the method comprising the steps of joining a core layer of an aluminium alloy, a filler alloy layer not containing flux particles, a flux composite layer of a matrix of aluminium or an aluminium alloy, said matrix containing flux particles, and an aluminium or aluminium alloy layer not containing flux particles forming the outermost surface of at least one side of the brazing sheet and the flux composite layer being positioned between said filler alloy layer and said aluminium or aluminium alloy layer, followed by rolling to obtain a brazing sheet of the desired gauge.

12. Brazing sheet as claimed in claim 1, wherein the filler alloy layer is an AA4XXX alloy.

13. Brazing sheet as claimed in claim 1, wherein the core layer is an AA2XXX, AA3XXX, AA6XXX, AA7XXX, or AA8XXX alloy.

14. Brazing sheet comprising a core layer and a braze cladding, said core layer being aluminium or an aluminium alloy, said braze cladding comprising (a) a flux composite layer, which flux composite layer comprises a matrix of aluminium or an aluminium alloy, said matrix containing flux particles; (b) a filler alloy layer not containing flux particles; and (c) an aluminium or aluminium alloy layer not containing flux particles, said layer forming the outermost surface of at least one side of the brazing sheet, wherein the flux composite layer (a) is positioned between said filler alloy layer (b) and said aluminium or aluminium alloy layer (c), wherein the aluminium or aluminium alloy of the core layer has a composition including less than or equal to 2 wt % Si, and wherein the filler alloy layer is an aluminium alloy including from 4 to 15 wt % of Si.

15. Brazing sheet as claimed in claim 14, wherein the aluminium or aluminium alloy layer (c) forming the outermost surface of at least one side of the brazing sheet is a filler alloy layer.

16. Brazing sheet as claimed in claim 14, wherein the aluminium or aluminium alloy layer (c) forming the outermost surface of at least one side of the brazing sheet is a non-filler aluminium or aluminium alloy layer.

17. Brazing sheet as claimed in claim 14, wherein the at least one filler alloy layer is an aluminium alloy comprising from 6 to 13 wt % of Si.

18. Brazing sheet as claimed in claim 14, wherein the matrix in the flux composite layer is aluminium or an AA1XXX, AA2XXX, AA3XXX, AA4XXXX, AA7XXXX, or AA8XXX aluminium.

19. Brazing sheet as claimed in claim 18, wherein the matrix in the flux composite layer is a filler alloy.

20. Brazing sheet as claimed in claim 18, wherein the matrix in the flux composite layer is aluminium or a non-filler aluminium alloy.

21. Brazing sheet as claimed in claim 14, wherein the amount of Mg in the matrix of the flux composite layer is wt %.

22. Brazing sheet as claimed in claim 14, wherein the flux is at least one inorganic salt comprising F and at least one of Li, Na, K, Rb, Cs, Fr, Al, Zn or Sn.

23. Brazing sheet as claimed in claim 14, wherein content of flux in the flux composite layer is from 1 to 20 wt %.

24. Brazing sheet as claimed in claim 14, wherein the filler alloy layer is an AA4XXX alloy.

25. Brazing sheet as claimed in claim 14, wherein the core layer is an AA2XXX, AA3XXX, AA6XXX, AA7XXX, or AA8XXX alloy.

Description

(1) FIG. 1 schematically shows an embodiments of a cladding plate according to the invention, while FIG. 2 schematically shows an embodiment of a brazing sheet according to the invention.

(2) Referring to FIG. 1, it is shown a cross section in the rolling direction of a cladding plate. The cladding plate comprises two filler alloy layers 1, 3 arranged on each side of a flux composite layer 2. Alternatively, one of the layers 1, 3, preferably the thinnest layer 3, may be a non-filler aluminium or aluminium alloy layer. Along the edges of the flux composite layer side sections 4 are arranged along the intended rolling direction. The filler alloy layer 1 is intended to face the core of a brazing sheet, while the thinnest filler alloy layer (or non-filler aluminium or aluminium alloy layer) 3 is intended to constitute the outermost surface of at least one side of a brazing sheet.

(3) Referring to FIG. 2, the brazing sheet comprises a core 5 with a braze cladding having two filler alloy layers 1, 3 arranged on each side of a flux composite layer 2. Alternatively, the outermost layer 3 may be a non-filler aluminium or aluminium alloy layer. The brazing sheet may be produced by attaching a cladding plate as shown in FIG. 1 followed by rolling and cutting off the side supports.

EXAMPLES

(4) The invention is further described in connection with the following Examples, which, however, is not intended to limit the scope of the invention.

(5) Materials

(6) In all examples a core material of Mg-free AA3003 was sampled from a non-homogenised slab having the composition: 0.14 wt % Si, 0.50 wt % Fe, 1.09 wt % Mn, 0.12 wt % Cu, balance Al and inevitable impurities. The core material was preheated with 80° C./h to 400° C., 20° C./h to 480° C. and soaked for 2 h before free cooling in air.

(7) The filler alloys used for the filler alloy layers were either AA4045 (Al with 10 wt % Si sampled from a hot breakdown rolled plate) or AA4343 (Al with 7.8 wt % Si sampled from a hot breakdown rolled plate).

(8) In Examples 1 and 2 the material for the flux composite layer was sampled from a body prepared by spray forming according to WO2008/110808 followed by extrusion and laboratory cold rolling. The aluminium alloy for the matrix of the flux composite layer was AA4045 and the flux was AlKF.sub.4.

(9) In Examples 3 and 4 the materials for the flux composite layer were sampled from bodies prepared by Hot Isostatic Pressing (HIP) of mixtures of metal powder and Nocolok® 100, a flux powder based on potassium fluoroaluminate. Both the chemical composition of the metal as well as the amount of flux was varied. The metal powders were produced through gas atomising using argon, giving a mean powder particle diameter of about 100 μm. The alloy and flux powders were carefully mixed to provide homogeneous blends filled into cylindrical aluminium cans that were hermetically sealed under vacuum. The hot isostatic pressing was made at a temperature of 500° C. at a pressure of 1000 Bar for 6 hours. After HIPing the cans were removed and the dense material extruded and laboratory cold rolled by the same procedure as the spray formed material in Examples 1 and 2.

(10) A 0.5 mm thick clad sheet consisting of Mg-free AA3003 core material clad with normal AA4045 with 10% clad ratio was tested as a reference material in brazing using the angle on coupon test. In the mini-HEX test (see Brazing tests) a 70 μm unclad corrugated Al alloy fin containing, in wt %, 0.8 Si, 0.23 Fe, 1.62 Mn, 1.5 Zn, and 0.12 Zr.

(11) Clad Package Production

(12) The core materials were laboratory cold rolled to a gauge suitable for pack rolling, i.e. roll application of additional metal alloy layers to provide a metallic laminated sheet. Then, the cores were heat treated at a temperature of 250° C.

(13) Filler alloy layers were made from pieces of AA4343 and AA4045 that were cold rolled down to gauges suitable for clad package rolling and then heat treated at a temperature of 380° C. Material for the flux composite layer was cold rolled to gauges suitable for clad package rolling and then heat treated at a temperature of 380° C. The cladding plates were made by combining the flux composite layer with one or several filler alloy layers using cold clad lab rolling to a thickness suitable for pack rolling and then heat treated at a temperature of 380° C.

(14) The cladding plates and the cores were then attached to each other using cold clad rolling and rolled to the final gauges. Finally, the clad samples were partially annealed at a temperature of 250° C. to H24 temper.

(15) The chemical compositions and thickness of claddings were determined using glow discharge optical emission spectroscopy (GDOES) and light optical microscopy. The amount of flux is expressed as the amount of AlKF.sub.4 and based on measurement of the content of K.

(16) Brazing Tests

(17) Depending on the total material thickness two different brazing tests were used based on two different test geometries. Either a miniature heat exchanger model (mini-HEX) was made and braze tested or a so-called angle-on-coupon (AOC) test was used in brazing. No additional flux was applied on any sample.

(18) In the angle on coupon test the clad material according to the invention were used as a flat coupon onto which an unclad 90° bent angle made from Mg-free AA3003 was attached. These tests were made in a glass brazing furnace. The heating rate from room temperature to the brazing temperature 600° C. was a linear 60° C./min followed by 1 min soaking at temperature and finalised by cooling in air. The nitrogen gas flow rate was set to 11 standard litres/min (SLM).

(19) For practical sample handling reasons and to simulate a real situation with better contact between the surfaces than in angle on coupon brazing, brazing sheets from each of the samples 7-12 prepared in Example 1 (i.e. the thinnest samples) were used as tube stock for making a mini-HEX. The mini-HEX was made from two parallel tube stock sheets according to the invention with 16 mm width and 200 mm length and a corrugated fin arranged between the plates. The package was held together using a suitable fixture. The brazing was made in a batch CAB furnace with an atmosphere that had <50 ppm O.sub.2 and a dew point of <−40° C. The heating cycle comprised heating from room temperature to 600° C. in 15 min and soaking for 3 min at that temperature before cooling to room temperature again.

(20) Four pieces of all samples were made. All brazed joints were inspected for stitches and other defect types and the brazing results were ranked on a scale 1-5. The best mark is 1 which means immediate wetting upon melting of the filler and excellent defect free joints, 2 means slightly slower wetting and joint formation but still defect free joints, 3 means longer time for wetting but acceptable joints with few defects that are of aesthetic character, 4 means one or more pieces had defect joints and 5 means that joining was absent.

Example 1 (Invention)

(21) Cladding plates with three layers were made using AA4045 filler alloy as a lid layer (filler alloy layer constituting the outermost surface of the final brazing sheet) and a base layer (filler alloy layer facing the core in the brazing sheet) and a flux composite layer with AA4045 as matrix positioned in between the lid and base layers. The resulting three layer cladding plates were attached to cores as indicated above. The sample matrix is seen in Table 1 and varies the product gauge, the cladding gauge, the flux composite layer clad ratio and thereby the flux composite layer gauge, the flux load and the total amount of filler alloy. This creates a variation in available flux amount and flux load as well as diffusion distance to the oxide/metal interface.

(22) The reference sample provided no brazed joints whereas all samples according to the invention, with a flux load as low as 0.05 g/m.sup.2 to be compared with 2-5 g/m.sup.2 generally recommended in commercial production, provided joints that were at least deemed acceptable and more often deemed to be very good.

(23) TABLE-US-00001 TABLE 1 Flux Approximative Total Cladding composite proportion of Flux Braze gauge gauge layer gauge lid:flux Load Braze result Sample [mm] [μm] [μm] composite:base [g/m.sup.2] test rank 1 0.5 56 6 1:1:8 0.29 AOC 1 2 0.5 51 12 1:2:7 0.77 AOC 1 3 0.5 52 14 1:3:6 1.22 AOC 1 4 0.35 38 4 1:1:8 0.24 AOC 1-2 5 0.35 37 8 1:2:7 0.50 AOC 1 6 0.35 36 11 1:3:6 0.81 AOC 1 7 0.2 23 3 1:1:8 0.11 mini-HEX 2-3 8 0.2 23 5 1:2:7 0.31 mini-HEX 1 9 0.2 21 6 1:3:6 0.56 mini-HEX 1 10 0.1 11 2 1:1:8 0.05 mini-HEX 3 11 0.1 10 3 1:2:7 0.14 mini-HEX 2-3 12 0.1 10 3 1:3:6 0.21 mini-HEX 2 Reference 0.5 50 0  0:0:10 0 AOC 5

Example 2 (Comparative)

(24) Two layered cladding plates were made consisting of a flux composite layer as in Example 1 combined with a filler alloy layer of AA4343 to form a two layered cladding on a core. Brazing sheets were made with different proportions of the braze cladding made up by the flux composite layer. Comparisons were also made between brazing sheets with the flux composite layer of the cladding facing the core surface (denoted as “core”) and brazing sheets with the flux composite layer constituting the outermost surface (denoted as “air”).

(25) The sample denotation and constitution as well as the braze results are shown in Table 2. Comparing the results of Tables 1 and 2, it appears that for samples with similar flux load the three layer braze claddings in Example 1 gave better braze results than the two layer braze claddings of this Example 2. It also appears that slightly better brazing results were obtained when the flux composite layer did not form the outer surface of the brazing sheet.

(26) TABLE-US-00002 TABLE 2 Total Flux Total clad Approximate composite Flux Braze gauge gauge proportion of flux layer gauge load Braze result Sample [mm] [μm] composite:AA4343 [μm] [g/m.sup.2] test rank 13 0.3 29 1:0 29 3.35 AOC 1 14 air 0.3 32 6:4 16 1.67 AOC 2-3 15 air 0.3 33 4:6 12 1.54 AOC 2-3 16 air 0.3 29 3:7 8 1.08 AOC 3-4 17 air 0.3 29 2:7 5 0.56 AOC 4-5 18 air 0.3 29 1:7 3 0.19 AOC 5 19 core 0.3 32 8:2 22 1.84 AOC 2 20 core 0.3 28 6:4 13 1.12 AOC 2 21 core 0.3 31 4:6 11 0.89 AOC 2 22 core 0.3 28 3:7 8 0.47 AOC 3 23 core 0.3 29 2:7 8 0.39 AOC 3 24 core 0.3 30 1:7 8 0.23 AOC 4 Reference 0.5 50 0:1 0 0 AOC 5

Example 3 (Invention)

(27) Cladding plates were prepared and attached to AA3003 cores in the same way as in Example 1, with the exception for the materials for the flux composite layer that had been prepared by HIP of various amounts of flux powder and metal powder of various aluminium alloys. Each cladding plate consisted of 10% AA4045 lid layer, 10% flux composite material, and 80% AA4045 base layer. The total gauge of the resulting brazing sheets was 0.3 mm, with a 30 μm braze cladding consisting of about 3 μm of lid filler alloy, 3 μm of flux composite and 24 μm of base filler alloy, on a 270 μm AA3003 core. AOC brazing tests were made as in Example 1. The alloy composition in wt % for the flux composites used and brazing results appear in Table 3 below:

(28) TABLE-US-00003 TABLE 3 Flux Braze load result No. Si Fe Mn Cu Mg Zn Zr Cr V Ti [g/m.sup.2] rank 1 8 0.20 ≤0.01 0.41 1 2 3.8 0.10 ≤0.01 0.87 2 3 8 0.20 ≤0.01 0.19 2 4 10 0.20 ≤0.01 1.01 1 5 10 0.20 ≤0.01 1.16 1 6 12.7 0.20 ≤0.01 1.38 1 7 14.6 0.20 ≤0.01 0.33 1 8 8.0 0.47 0.50 0.18 0.02 0.37 1 9 8.0 0.53 1.01 0.40 0.02 0.40 2 10 8.0 0.54 1.53 0.57 0.03 0.10 0.10 0.11 0.11 0.40 4 11 7.9 0.96 2.31 0.03 0.19 0.24 0.28 0.23 0.36 5 12 7.9 0.18 0.25 0.39 4-5) 13 8 0.20 0.4 0.32 5 14 9.7 0.21 ≤0.01 0.97 0.36 1 15 9.8 0.21 ≤0.01 4.1 0.45 1 16 10.1 0.20 ≤0.01 8.0 0.42 1

(29) In addition to the elements indicated in the Table, the balance was aluminium and ≤0.05 each and ≤0.15% in total of inevitable impurities.

Example 4 (Invention)

(30) A cladding plate was prepared and attached to AA3003 cores in the same way as in Example 3, with the exception for the lid alloy that was AA1050 (0.19 wt % Si, 0.22 wt % Fe, balance Al and inevitable impurities). The base layer was AA4045 as in Example 1 and the material for the flux composite was the same as in No. 1 in Table 3. The flux load was 0.4 g/m2 and the result of the same brazing test as in Example 3 was ranked as 2.