Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2000-07-20
2002-09-17
Koehler, Robert R. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C138S140000, C148S516000, C148S519000, C148S523000, C148S535000, C148S550000, C148S552000, C148S689000, C148S692000, C148S439000, C165S905000, C420S534000, C420S535000, C420S553000, C428S606000, C428S607000, C428S577000, C428S034100, C428S933000
Reexamination Certificate
active
06451453
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to strips or thin drawn tubes (of thickness generally between 0.1 and 1.5 mm) made of aluminum-manganese alloy (3000 series according to the nomenclature of the Aluminum Association), possibly coated on one or two surfaces with a covering alloy, most commonly an aluminum-silicon brazing alloy (4000 series according to the nomenclature of the Aluminum Association). These strips and tubes are intended for the manufacture of elements, such as tubes, fins, collectors and plates, for heat exchangers assembled by brazing, these exchangers being used particularly in the cooling systems of engines and air-conditioning systems for the interiors of automobiles. The techniques for brazing aluminum alloys are described, for example, in the article by J. C. Kucza, and J. C. Goussain “Le brasage fort de l'aluminium et ses alliages”, that appeared in Soudage et Techniques Connexes, November-December. 1991, pp. 18-29. The strips or tubes according to the invention are used notably in the brazing techniques with non-corrosive flux of the NOCOLOK® or CAB (Controlled Atmosphere Brazing) type.
DESCRIPTION OF RELATED ART
The use of aluminum alloys in heat exchangers of automobiles has developed during the last few years, notably because of the weight benefit that it provides compared with the use of copper based alloys. The required properties for strip or tubes made of aluminum alloy that are used for the manufacture of brazed exchangers are notably good brazeability, high mechanical strength after brazing, so that the thickness used is a small is possible, the tubes, fins, collectors and plates should be easy to form, and there should be good resistance to corrosion. Of course, it is important that the alloy chosen should be easy to cast and to roll or draw, and that the cost of producing strip or tubes should be compatible with the demands of the automobile industry.
The alloy currently used as a base alloy is 3003 of composition (% by weight according to Standard EN 573-3):
Si<0.6 Fe<0.7 Cu: 0.05-0.20 Mn: 1.0-1.5 Zn<0.10 other elements each <0.05 and <0.15 in total; balance aluminum. Numerous alloys have been proposed in the course of the last few years to improve one or other of the using properties mentioned previously, in particular the corrosion resistance, from which comes the name “long-life” alloys which is sometimes given to them in the trade.
Patent FR 2564962 (=U.S. Pat. No. 4,673,551) from Sumitomo Light Metal Industries relates to a base alloy for fins for high pressure exchangers with the composition (% by weight):
Si: 0.05-0.30 Fe<0.8 Cu: 0.1-1 Mn: 0.6-1.5 Mg: 0.1-0.75 and possibly Zr, Ti, Cr or V at levels of <0.25%.
U.S. Pat. No. 5,125,452 (Sumitomo Light Metal Industries and Nippondenso) describes coated strip with the base alloy having the composition:
Si<0.1 Fe<0.3 Cu: 0.05-0.35 Mn: 0.3-1.5 Mg: 0.05-0.5 Ti: 0.05-0.35 with Cu−0.2<Mg<Cu+0.2.
Patent EP 0326337 (Alcan International) describes coated strip with the base alloy having the composition:
Si<0.15 Fe<0.4 Cu: 0.1-0.6 Mn: 0.7-1.5 Mg<0.8
The low Si content, preferably <0.05%, allows the formation of a dense layer of precipitates with Mn, which plays the role of a barrier to the diffusion of the silicon from the coating alloy, and increases the corrosion resistance. WO 94/22633 is a variant of the preceding patent which only differs in having a higher Cu content (0.6-0.9%).
U.S. Pat. No. 5,350,436 (Kobe Alcoa and Nippondenso) describes a base alloy of composition: Si: 0.3-1.3 Cu<0.2 Mn: 0.3-1.5 Mg<0.2 Ti: 0.02-0.3 Fe not being mentioned.
The high Si content (0.8% in the examples) permits one to compensate for the absence of Cu and Mg for mechanical strength. The presence of Ti and the absence of Mg contributes to good corrosion resistance.
Patent EP 0718072 (Hoogovens Aluminium Walzprodukte) describes a base alloy of composition:
Si<0.15 Fe<0.8 Cu: 0.2-2 Mn: 0.7-1.5 Mg: 0.1-0.6 with Cu+Mg<0.7 and a possible addition of Ti, Cr, Zr or V. The examples show Si contents of 0.5%.
To summarize what is known from the state of the technology for this type of alloy, a first category of alloys is noted which have a very low Si content (<0.15 and preferably <0.05%) and which may or may not have a Fe content which is low, but which, in all cases, is less strictly defined than the Si level. These very low Si levels can only be obtained by starting from pure bases, which has an adverse effect on the manufacturing costs. A second category of alloys, which calls into question the need for a very low Si content to obtain good corrosion, has, on the contrary, a rather high Si content (0.5 to 0.8%) possibly, in order to compensate for the loss of mechanical strength linked to low levels of hardening elements Mg and Cu. In effect, for brazing with a flux, it is known that the Mg content must be reduced, in order to prevent migration of Mg to the surface of the coating layer, which leads to the formation of a thick layer of oxide MgO. The presence of this oxide requires one to increase the quantity of flux on the surfaces to be brazed, which increases the costs of assembly and causes a deterioration in the appearance of the surface. As for Cu, its influence on corrosion resistance is much debated.
SUMMARY OF INVENTION
The applicant has determined a region of composition that allows one to further improve the compromise between the various using properties (mechanical strength, ductility, corrosion resistance and brazeability) while all the time remaining within acceptable economic constraints, by linking a narrow region of Si content situated between those disclosed in the two categories of alloys of the prior art, and a reduced level of Fe, which nevertheless remains at a reasonable level that does not require a pure base.
Hence, a subject of the invention is a strip or a thin drawn tube, intended for the manufacture of brazed heat exchangers, made of an alloy of composition (% by weight):
Si: 0.15-0.30 Fe<0.25 Cu: 0.2-1.1 Mn: 1.0-1.4 Mg<0.4 Zn<0.2 Ti<0.1 other elements each <0.05 and <0.15 in total, remainder aluminum with Fe≦Si and Cu+Mg>0.4.
This strip or this tube can be coated on one or both surfaces with an aluminum alloy, most commonly a AlSi brazing alloy containing from 5 to 13% of Si.
Another subject of the invention is 3 particular regions, within the general region of composition of the base alloy, that allow one to favor a particular property:
a) Cu: 0.2-0.6 Mg: 0.1-0.4
b) Cu: 0.6-1.1 Mg: 0.1-0.4
c) Cu: 0.4-0.7 Mg<0.01
REFERENCES:
patent: 4649087 (1987-03-01), Scott et al.
patent: 4673551 (1987-06-01), Sugiyama et al.
patent: 5041343 (1991-08-01), Fortin et al.
patent: 5125452 (1992-06-01), Yamauchi et al.
patent: 5422191 (1995-06-01), Childree
patent: 0718072 (1996-06-01), None
patent: 09268339 (1997-10-01), None
patent: 9422633 (1994-10-01), None
Hoffmann Jean-Luc
Kucza Jean-Claude
Morere Bruce
Shahani Ravi
Dennison, Scheiner & Schultz
Koehler Robert R.
Pechiney Rhenalu
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