Aluminum brazing alloy

Details Aluminum brazing alloy Aluminum brazing alloy

2002-05-13

2003-08-26

King, Roy (Department: 1742)

Alloys or metallic compositions

Aluminum base

Silicon containing

C420S551000, C420S553000

Reexamination Certificate

active

06610247

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to an aluminium alloy, which alloy can be used for heat exchangers. Ideally the aluminium alloy according to the invention is provided as fin stock material for heat exchanger devices. Furthermore, the invention relates a brazed assembly in the form of a brazed heat exchanger comprising at least one component of the aluminium alloy according to this invention.
DESCRIPTION OF THE RELATED ART
In the prior art, aluminium alloys are the alloys of choice for heat exchanger applications. These alloys are selected for their desirable combination of strength, low weight, good thermal and electrical conductivity, brazeability, corrosion resistance, and formability.
An aluminium alloy heat exchangers can be fabricated by stacking aluminium alloy clad sheets (brazing sheet), which have been formed to a desired configuration, so as to form fluid passages (tubes) and securing corrugated aluminium alloy fins between fluid passages by brazing. The bonding between the alloy clad sheets or the tube material and fins is achieved by melting the brazing filler metal of the core plates and/or fin material. As a brazing method, typically vacuum brazing or flux brazing is being applied. In an effort to improve the corrosion resistance of the fluid passage materials, some fin materials may be used which are electrochemically anodic (less noble) relative to the fluid passage material by the sacrificial anode effect of these fin materials.
Some disclosures of aluminium brazing sheet alloys found in the prior art literature will be mentioned below.
The publication by J. Althoff, in the technical journal Light Metal Age, December, 1980, pp. 20-21, “Aluminium Alloy 3009: High Strength Without Magnesium”, discloses the 3009 alloy without magnesium. The 3009 alloy has the following composition, in weight percent:
Si
1.0-1.8
Fe
max. 0.7
Cu
max. 0.10
Mn
1.2-1.8
Mg
max. 0.01
Cr
max. 0.05
Ni
max. 0.05
Zn
max. 0.05
Zr
max. 0.10
Ti
max. 0.10
others each max. 0.05, total max. 0.15
balance aluminium,
and further has the proviso that Si:Fe should be 2:1 to 4:1,
and that Mn+Si should be in the range of 2.5-3.5.
The disclosed alloy may replace the known AA3003 alloy, and may be used for brazing applications.
EP-A-0637481 (Furukawa) discloses an aluminium alloy brazing sheet having a three-layer structure clad one side of the core material with a brazing material and clad of the other side of the core material with a sacrificial material. The defined core material has a very wide compositional window, in weight percent:
Si
0.6-2.5
Cu
0.5-2.5
Mn
up to 2.0
at least one kind selected from the group consisting of:
Mg
0.03-0.5
Cr
0.03-0.3
Zr
0.03-0.3
Ti
0.03-0.3
Ni
0.03-1.5
balance aluminium and impurities.
This document further discloses an aluminium alloy brazing sheet having a three-layer structure cladded on both sides of the core material with a brazing material and whereby the core material has a very wide compositional window, in weight percent:
Si
0.03-2.5
Fe
0.05-2.0
Cu
0.05-2.0
Mn
 0.6-2.0
at least one kind selected from the group consisting of:
Zn
 0.05-5.0
In
0.002-0.3
Sn
0.002-0.3
balance aluminium and inevitable impurities.
There is a market demand in the automotive industry for aluminium alloys which alloys may be used for application in heat exchangers, and which alloys have improved post-brazed strength in combination with a good corrosion resistance. Further, there is a demand for fin stock alloy or aluminium braze product having a melting point or solidus temperature of the material greater than the current commercially available brazing process for which it will be applied, whereby both vacuum and controlled atmosphere brazing (“CAB”) presently use aluminium alloys containing high levels of silicon with melting temperatures ranges from about 555 to 610° C. Furthermore, there is a demand from the side of the manufacturers of such aluminium alloys, for alloys having a tolerance for impurity elements from a recycling point of view without compromising to the required balanced properties of such an aluminium alloy.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an aluminium alloy which can be used for heat exchangers having an improved post-braze 0.2% yield strength over conventional alloys for the same application. It is another object of the present invention to provide an aluminium alloy having an improved tolerance for impurity elements. It is a further object of the present invention to provide an aluminium alloy which alloy is ideally suitable for providing fin stock material for heat exchanger devices, and having a solidus temperature of greater than about 610° C.
In one aspect the invention provides an aluminium alloy having the composition, in weight percent:
Si
0.4-1.0
Mn
0.7-1.2
Mg
up to 0.10
Fe
up to 0.8
Zn
up to 3.0
Ni
0.5-0.9
Cu
up to 0.15
Ti
up to 0.20
In
up to 0.20
Zr
up to 0.25
V
up to 0.25
Cr
up to 0.25
others up to 0.05 each, up to 0.15 in total
A1
balance.
This aluminium alloy has a good corrosion resistance, which includes the sacrificial anode effect where required, in combination with good mechanical properties in the post-brazing state and is capable of providing an increase in post-braze 0.2% yield strength (PS) of at least 15% over conventional finstock alloys, such as AA3003 in the same temper. The aluminium alloy in accordance with the invention is capable of achieving a post-braze 0.2% yield strength (PS) of at least 55 MPa, and in the best examples of at least 60 MPa. Furthermore, the aluminium alloy has after hot and/or cold rolling a desirable solidus temperature or melting temperature of 610° C. or higher.
Although this aluminium alloy can be used for tube plate, side supports and header tanks in heat exchanger units, and may have other uses, it is primarily intended as a rolled finstock alloy for heat exchangers. The corrosion demand for finstock is such that if the heat exchanger unit is attacked by corrosion, the fin material is preferentially attacked and not the tube material. The aluminium alloy according to this invention has this sacrificial anode effect. The aluminium alloy can be stronger, so the rolled finstock can be thinner and lighter than conventional finstock alloys, such as AA3003 alloys. The aluminium alloy of the invention used as finstock material may be used in combination with a cladding of a brazing alloy, e.g. an Al—Si alloy known in the art or other similar Al—Si systems alloys, such as Al—Si—Mg alloy, Al—Si—Mg—Bi alloy, Al—Si—Bi alloy or the like.
The heat exchanger market, particularly in the automotive industry, requires that finstock alloys offer a balance of properties, i.e. strength, formability, brazeability, corrosion potential and high solidus temperature. Our present evaluations have shown that the Si, Mn, Ni, Cu and Mg levels must be controlled and are key to the overall balanced performance of the materials. One of the key features of the novel alloy of this invention is the relatively high Si content as compared to AA3003 alloys, in combination with a medium Mn content. Consequently this increases the post-braze strength, by more than 15% relative to conventional finstock alloys. The aluminium alloy exhibits amongst other features excellent brazeability properties in combination with a high solidus temperature of 610° C. or higher.
The reasons for the limitations of the important alloying and other elements of the aluminium alloy according to the present invention are described below. Unless mentioned otherwise, all composition percentages are by weight.
Si is an important alloying element in the alloy according to this invention. The addition of Si results in an increased solution hardening of the alloy. Below 0.4% there is only little effect of the Si, and above 1.0% it may result in the formation of detrimental low-melting eutectics and also in the formation of large intermetallic particles. A more suitable range for the Si content is 0.65 to 1.0%, and more preferably in the range of 0.70 to 0.95%. In many aluminium alloys a Si-level at a medium

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