Metal treatment – Process of modifying or maintaining internal physical... – Producing or treating layered – bonded – welded – or...
Reexamination Certificate
2000-11-09
2002-07-02
Wyszomierski, George (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Producing or treating layered, bonded, welded, or...
C148S535000, C228S262510
Reexamination Certificate
active
06413331
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an aluminum alloy for use in a brazed assembly as a core material in brazing sheet, to the use of the aluminum alloy as core material of a brazing sheet in a brazed assembly, to the use of the aluminum alloy as fin stock material, to a method for manufacturing a brazed assembly, as well as to an assembly thus manufactured. The aluminum alloy is of the Aluminum Association 3xxx-type. Herein the term sheet material includes tube material, plate material and header material.
DESCRIPTION OF THE PRIOR ART
A principle use of brazing sheet containing such alloy is in heat exchangers, such as radiators, condensers and oil coolers. These heat exchangers are exposed to a severe external corrosive attack by e.g. deicing road salt. For that reason a good corrosion resistance is an essential property. Long-life alloys are considered herein as those which in the Sea Water Acidified Accelerated Test (SWAAT) without perforations according to ASTM G-85 exceed 10-12 days (see K. Scholin et al., VTMS 1993, SAE P-263). A further important property of the brazing sheet is the strength after brazing, hereafter referred to as the post-brazed strength.
WO 94/22633 describes such an alloy, having the composition, in weight %:
Mn
0.7-1.5
Cu
0.5-1.0, preferably > 0.6-0.9
Fe
not more than 0.4
Si
not more than 0.15
Mg
up to 0.8
V and/or Cr
up to 0.3, preferably up to 0.2
Ti
up to 0.1
balance aluminum and impurities.
This alloy is used as core material with brazing clad layers containing Si. The high Cu content is to improve post-brazed strength. Ti is preferably not deliberately added, though is typically present from source material. Preferably Zr is not deliberately added. Cr and/or V are said not to improve post-brazed corrosion resistance, but contribute to post-brazed strength and sag resistance. The brazing sheet of WO 94/22633 has a reported post-brazed yield strength in the range of 54-85 MPa.
EP-A-0718072 discloses a brazing sheet having a core sheet made of an aluminum alloy core material and on at least one side thereof a brazing layer of an aluminum alloy containing silicon as main alloying element, wherein the aluminum alloy of the core sheet has the composition (in weight %):
Mn
0.7-1.5
Cu
0.2-2.0
Mg
0.1-0.6
Si
>0.15, preferably > 0.20, and most preferably > 0.40
Fe
up to 0.8
Ti
optional, up to 0.15
Cr
optional, up to 0.35
Zr
and/or V optional, up to 0.25 in total
balance aluminum and unavoidable impurities, and with the proviso that (Cu+Mg)>0.7.
The disclosed core alloy has a Si-level of more than 0.15%, and most preferably of more than 0.40%, in order to achieve the desired strength levels while maintaining a good corrosion resistance.
EP-A-0537764 discloses a method of producing aluminum alloy heat-exchanger in which a brazed assembly after brazing is cooled and then reheated for 10 minutes to 30 hours at a temperature in the range of 400 to 500° C. This additional heat treatment after brazing is in order to deposit elements (e.g. Si, Mg and Mn) which are brought into solid solution during the brazing cycle, and is said to improve the thermal conductivity of the material and thereby improving the thermal efficiency of the heat-exchanger obtained by about 3%. The core alloy used comprises not more than 0.5% of Cu and further comprises Si as an alloying element in the range of 0.05 to 1.0%.
U.S. Pat, No. 4,214,925 discloses a method for fabricating a brazed aluminum fin heat exchanger, in which the fins have a composition comprising 0.15 to 0.40 weight % of Cu, and is preferably of the heat-treatable AA6951 alloy, and in which the core sheet material of the brazing sheet is of the conventional AA3003 alloy. The cooling rate after solution heat-treatment for 30 minutes to 4 hours at 500 to 570° C., is in the range of 2.8 to 50° C./min, preferably 2.8 to 20° C./min, and more preferably about 10° C./min.
The later published international patent application no. PCT/EP97/06070 mentions a non-heat treatable aluminum alloy as core alloy in brazing sheet, i.e. it does not require post-brazing ageing treatment. Said aluminum core alloy, consisting of, in weight %:
Mn
0.7-1.5
Cu
0.6-1.0
Fe
not more than 0.4
Si
less than 0.1
Mg
0.05-0.8
Ti
0.02-0.3
Cr
0.1-0.35
Zr
0.1-0.2
balance aluminum and unavoidable impurities, and wherein 0.20≦(Cr+Zr)≦0.4.
SUMMARY OF THE INVENTION
An object of the invention is to provide an aluminum alloy for use in a brazed assembly, in particular as core alloy in brazing sheet or as fin stock material, providing improved strength properties in combination with good corrosion resistance.
According to the invention, there is provided an aluminum alloy in the form of a sheet, plate or extrusion, having a composition in the range (in weight %):
Si
<0.15
Mn
0.7-1.5
Mg
up to 0.8
Cu
0.5-1.5
Fe
<0.4
Cr
<0.30
Zr
<0.30
Ti
<0.30
V
<0.30
others
each < 0.05, total < 0.15
balance
aluminum
and said aluminum alloy is provided in an aged condition.
In accordance with the invention it has surprisingly been found that the aluminum alloy appears to be age hardenable in the post-brazed condition, both by means of natural ageing and by artificial ageing. This ageing effect after brazing was yet undiscovered and is untypical for standard AA3xxx type alloys. It gives the possibility of a significant increase of the obtainable post-brazed yield strength in a range of 5 to 35 MPa over the post-brazed yield strength reported in the prior art, while the good corrosion resistance remains unchanged after the ageing treatment.
According to the invention the aluminum alloy is capable of providing a 0.2% yield strength of at least 75 MPa after brazing and ageing, and has a corrosion resistance of 13 days or more in SWAAT without perforations in accordance with ASTM G-85.
In a more preferred embodiment the aluminum alloy is capable of providing a 0.2% yield strength of at least 80 MPa after brazing and ageing, and more preferably of at least 85 MPa after brazing and ageing.
In the best examples, this corrosion resistance is more then 20 days. This level of corrosion resistance qualifies the alloy as a long-life product. Further, in the best examples, the provided 0.2% yield strength after brazing and the ageing is at least 95 MPa. Typically, but not by means of limitation, brazing is performed at about 590 to 600° C. for 3 to 5 min.
The aluminum alloy is of the AA3xxx type, Mn being the main alloying element in order to obtain the desired strength level. At least 0.7% is required for obtaining the desired strength, while a Mn content of over 1.5% does not produce any significant improvements in respect strength because coarse Al—Mn-containing particles are formed. A further disadvantage of coarse Al—Mn-containing particles is that they reduce the rollability of the aluminum alloy. More preferably the Mn content is in a range of 0.8 to 1.2%.
Magnesium is used in core alloys for brazing sheet to improve strength in vacuum brazed products. If a flux brazing process is applied, the Mg content is preferably kept at a low level, and preferably lower than 0.4%. In a further embodiment a Mg content of zero is preferred in flux brazing processes in which the brazability is improved. The Mg content is specified as up to 0.8% maximum and preferably 0.5% maximum.
The Si content in the aluminum alloy of this invention should be less than 0.15% in order to obtain long-life corrosion performance, and is preferably less than 0.10%. In an even more preferred range the Si is present at impurity level. Despite the low Si content a significant ageing effect is observed.
The Cu content in the aluminum alloy increases the strength of the alloy and should be in the range of 0.5 to 1.5%, and is preferably larger than 0.7%. In particular in this range in combination with a low Si content and in combination with Mg, the unexpected ageing effect has been observed, while the desired long-life corrosion resistance does not decrease significantly. With a Cu content of over 1.5% undesired coarse Cu-containing particles can be formed, as w
Bürger Achim
Hurd Timothy John
Kooij Nicolaas Dirk Adrianus
Vieregge Klaus
Corus Aluminium Walzprodukte GmbH
Stevens Davis Miller & Mosher LLP
Wyszomierski George
LandOfFree
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