Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1999-10-06
2001-07-17
Zimmerman, John J. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S933000, C165S133000, C165S134100, C165S905000
Reexamination Certificate
active
06261706
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an aluminum alloy clad material for heat exchangers exhibiting high strength and excellent corrosion resistance. More particularly, the present invention relates to an aluminum alloy clad material for heat exchangers exhibiting high strength and excellent corrosion resistance which is suitable as a material for a fluid passage (tube material) and a header plate material for automotive heat exchangers, such as a radiator or heater, joined by brazing using a fluoride-type flux or vacuum brazing, and is also suitable as a piping material connected to such heat exchangers.
2. Description of Background Art
As a tube material or header plate material for automotive heat exchangers such as a radiator or heater, a three-layered aluminum alloy clad material comprising a core material of an Al—Mn alloy such as a JIS3003 alloy which is clad with a brazing material of an Al—Si alloy on one side and a sacrificial anode material of an Al—Zn alloy or Al—Zn—Mg alloy clad on the other side has been used.
The Al—Si brazing material is clad to join a tube to a fin or header plate by brazing. As a brazing method, brazing in an inert gas atmosphere using a fluoride-type flux or vacuum brazing is employed. The sacrificial anode material constitutes the inner surface of the core material and exhibits a sacrificial anode effect by being in contact with a working fluid during use of a heat exchanger, thereby preventing pitting or crevice corrosion in the core material. The fin which is joined to the outer surface of the tube prevents the core material from being corroded by exerting the sacrificial anode effect.
In view of a reduced weight for automotive heat exchangers, the tube material has been provided with high strength by adding Cu to the core material, or by causing Mg and Si to coexist to produce an Mg
2
Si compound in the core material and the sacrificial anode material to decrease the thickness of the tube material. Zn in the sacrificial anode material and Cu in the core material interdiffuse when heated for brazing and greatly affect the corrosion resistance. Because of this, the interdiffusion between Zn in the sacrificial anode material and Cu in the core material during heating for brazing has been taken into consideration to provide a clad material with excellent corrosion resistance and improved strength after brazing.
For example, a clad material in which the combination between the thickness of the sacrificial anode material layer and the Zn content is optimized (Japanese Patent No. 2,572,495), and a clad material exhibiting improved corrosion resistance in which the sacrificial anode material contains Zn and the core material contains less than 0.7% of Cu to set the potential difference between the core material layer and the sacrificial anode material layer at 30-120 mV (Japanese Patent Application Laid-open No. 023535/1994) have been proposed. A clad material provided with improved strength and corrosion resistance by adjusting the thickness of the sacrificial anode material layer to 46-70 &mgr;m and adding 0.7-2.5% of Cu has also been proposed (Japanese Patent Application Laid-open No. 134574/1996).
A two- or three-layered aluminum alloy clad tube comprising a core material of an Al—Mn alloy such as a JIS3003 alloy clad with a sacrificial anode material of a Al—Zn alloy such as a JIS7072 alloy on either one side or both sides has been used for the passage connecting the automotive heat exchangers. The sacrificial anode material on the inner surface of the clad tube is in contact with a working fluid during use of a heat exchanger and exhibits the sacrificial anode effect, thereby preventing pitting or crevice corrosion in the core material. The sacrificial anode material on the outer surface prevents pitting or crevice corrosion in the core material, which occurs when used under severe conditions.
After brazing, the above conventional aluminum alloy clad materials for heat exchangers exhibit a potential gradient from the surface of the sacrificial anode material layer to the core material owing to interdiffusion between Zn in the sacrificial anode material and Cu in the core material. Corrosion spreads laterally in the direction of the plate width in such a gradient material having the potential gradient, whereby corrosion proceeds slowly to provide the material with excellent corrosion resistance.
However, the effective ranges for securing corrosion resistance in this method are limited because of limitations to the amount of Cu to be added to the core material, or requirement for providing the sacrificial anode material layer with a greater thickness in order to add a greater amount of Cu. If the thickness of the tube material is further reduced, corrosion resistance may be insufficient.
SUMMARY OF THE INVENTION
The present inventors have conducted experiments and studies on corrosion of a gradient material produced by the interdiffusion of Zn of a sacrificial anode material and Cu of a core material. As a result, the inventors have found that large Si compounds and Fe compounds with a potential higher than the matrix present in the sacrificial anode material matrix hinder the gradient function around these compounds as local cathodes, and cause preferential corrosion, thereby preventing corrosion from spreading in the lateral direction.
The present invention has been achieved on the basis of the above findings. In order to provide superior strength and excellent corrosion resistance to a gradient material having a potential gradient from the surface of the sacrificial anode material layer to the core material, which is produced by the interdiffusion of Zn of the sacrificial anode material and Cu of the core material, the inventors have further examined compositions for the core material and sacrificial anode material, combinations thereof, and the relation between the distribution of the compounds in the sacrificial anode material matrix and the performances. Accordingly, an object of the present invention is to provide an aluminum alloy clad material for heat exchangers exhibiting high strength and excellent corrosion resistance which is suitable as a tube material, header plate material, and piping material for heat exchangers, in particular, automotive heat exchangers.
In order to achieve the above object, an aluminum alloy clad material for heat exchangers exhibiting high strength and excellent corrosion resistance according to the present invention comprises a sacrificial anode material clad on one side of a core material, wherein the core material comprises an aluminum alloy comprising 0.3-2.0% of Mn, 0.25-1.0% of Cu, 0.3-1.1% of Si, and 0.05-0.35% of Ti with the remaining portion consisting of aluminum and impurities, the sacrificial anode material comprises an aluminum alloy comprising 1.5-8% of Zn, 0.01-0.8% of Si, and 0.01-0.3% of Fe with the remaining portion consisting of aluminum and impurities, and the total number of particles of Si compounds and Fe compounds with a particle diameter (circle equivalent diameter) of 1 &mgr;m or more present in the sacrificial anode material matrix is 2×10
4
or less per 1 mm
2
.
A second feature of the present invention is an aluminum alloy clad material comprising a sacrificial anode material clad on one side of a core material and a brazing material of an Al—Si alloy clad on the other side of the core material, wherein the core material comprises an aluminum alloy comprising 0.3-2.0% of Mn, 0.25-1.0% of Cu, 0.3-1.1% of Si, and 0.05-0.35% of Ti with the remaining portion consisting of aluminum and impurities, the sacrificial anode material comprises an aluminum alloy comprising 1.5-8% of Zn, 0.01-0.8% of Si, and 0.01-0.3% of Fe with the remaining portion consisting of aluminum and impurities, and the total number of particles of Si compounds and Fe compounds with a particle diameter (circle equivalent diameter) of 1 &mgr;m or more present in the sacrificial anode material matrix is 2×10
4
or less per 1 mm
2
.
A third feature of t
Fukuda Sunao
Ikeda Hiroshi
Kamiya Yoshihiko
Shoji Yoshifusa
Tanaka Hirokazu
Denso Corporation
Flynn Theil Boutell & Tanis, PC
Zimmerman John J.
LandOfFree
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