Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1999-10-14
2001-11-13
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, C138S141000, C138S143000, C428S650000, C428S686000, C428S457000, C428S933000
Reexamination Certificate
active
06316126
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an aluminum alloy clad material for heat exchangers exhibiting excellent erosion-corrosion resistance. The aluminum alloy clad material comprises an aluminum alloy clad sheet for heat exchangers exhibiting excellent erosion-corrosion resistance which comprises the aluminum alloy clad material and is suitably used for forming a tube material or header plate material in the manufacture of aluminum heat exchangers such as a radiator and heater by brazing in an inert atmosphere using a fluoride-type flux or vacuum brazing, and an aluminum alloy clad pipe comprising the aluminum alloy clad material which is used for tubes for circulating a working fluid in the aluminum heat exchanger such as a radiator and heater and for a pipe connected to heat exchangers, and is mechanically assembled into a fin of a heat exchanger using a pipe expansion method and the like.
2. Description of Background Art
As a tube material or header plate material for an automotive radiator, heater, and the like, a two-layered clad sheet comprising a core material of an Al—Mn alloy such as a 3003 alloy clad with a brazing material of Al—Si alloys or a sacrificial anode material of an Al—Zn alloy or an Al—Zn—Mg alloy on the outer side has been used. In some cases, a three-layered clad sheet comprising a core material of an Al—Mn alloy such as a 3003 alloy 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.
In the manufacture of a radiator or heater, tubes are formed by curving the clad sheet with the brazing material of an Al—Si alloy or the core material being on the outer side and welding or brazing the clad material. The tube is joined to a fin or header plate via the brazing material of the tube material or a brazing material clad on the fin by inert atmosphere brazing using a fluoride-type flux or vacuum brazing. The sacrificial anode material on the inner surface of the tube material exhibits a sacrificial anode effect by being in contact with a working fluid during use to prevent occurrence of pitting or crevice corrosion of the core material. The fin material prevents the core material from pitting by exerting a sacrificial anode effect on the core material.
A clad pipe with a two-layered structure in which an Al—Zn alloy as an inner layer (sacrificial anode material layer) is clad on an Al—Mn alloy such as a 3003 alloy as an outer layer (core material layer), or a clad pipe with a three-layered structure in which an outermost layer (sacrificial anode layer) of an Al—Zn alloy is further clad on the outside the piping material has been also used. In this case, the inner layer of the clad pipe exhibits a sacrificial anode effect on the core material layer of an Al—Mn alloy by being in contact with the working fluid to prevent the core material layer from pitting. In the case of the clad pipe with a three-layered structure, the outermost layer prevents occurrence of pitting or crevice corrosion of the core material layer by exerting a sacrificial anode effect on the core material layer made of an Al—Mn alloy.
As a working fluid for heat exchangers and pipes, a neutral or weak alkaline solution prepared by diluting a commercially available antifreeze fluid containing ethylene glycol as an essential component with water to a concentration of 50 vol % is commonly used. Some working fluids may cause erosion-corrosion in the aluminum alloy clad material (clad sheet and clad pipe) constituting a tube, and the corrosion perforates the core material or core material layer to impair heat exchanging properties.
Some materials for aluminum heat exchangers such as a radiator or heater exhibiting improved pitting resistance have been proposed. One of such materials is an aluminum alloy clad material made of a core material of an Al—Mn alloy containing 0.2-1.5% of Mn, 1.0% or less of Si, and one or more of 0.5% or less of Cu, 0.3% or less of Cr, and 0.2% or less of Zn as required, a brazing material of an Al—Si alloy clad on one side of the core material, and a sacrificial anode material of an aluminum alloy containing 2% or less of Zn clad on the other side of the core material (Japanese Patent Application Laid-open No. 94993/1991). The other example is an aluminum alloy clad material made of a core material of an aluminum alloy containing 0.3-2% of Mg, 0.3-1.5% of Si, 0.02-0.8% of Cu, and one or more of 0.05-0.3% of Mn, 0.02-0.5% of Cr, and 0.02-0.2% of Zr as required, a conventional brazing material of an Al—Si alloy clad on one side of the core material, and a sacrificial anode material of an aluminum alloy containing 0.2-3% of Zn, 0.005-0.05% of In, and 0.05-0.2% of Sn clad on the other side of the core material (Japanese Patent Application Laid-open No. 132284/1996).
These aluminum alloy clad materials exhibit an excellent sacrificial anode effect as a tube material for a radiator or heater, if the working fluid is neutral or weakly acidic and includes a Cl ion and has a relatively low temperature. However, if the working fluid is weakly alkaline and flows inside a heat exchanger at a high velocity, these materials exhibit insufficient corrosion resistance, thereby causing erosion-corrosion due to the insufficient anti-corrosion effect.
SUMMARY OF THE INVENTION
The present inventors have conducted studies on the corrosion mechanism of an aluminum alloy clad material comprising a sacrificial anode material clad on a core material in a weak alkaline solution, and examined countermeasures for preventing corrosion. As a result, the inventors have found that a brown or black film which is formed on the surface of a sacrificial anode material layer under weak alkaline conditions is removed by the impact of a high-velocity working fluid. The area where such a film is removed is preferentially corroded, thereby resulting in through-holes.
On the basis of the above findings, the present invention has been achieved as a result of diversified experiments and examinations in order to find a combination of a sacrificial anode material and a core material exhibiting excellent corrosion resistance in which the surface of the sacrificial anode material is protected to prevent a brown or black film from being produced under conditions where a weak alkaline working fluid flows at a high velocity. An object of the present invention is to provide an aluminum alloy clad material for heat exchangers which exhibits excellent erosion-corrosion resistance, does not produce through-holes due to erosion-corrosion under conditions where a weak alkaline working fluid flows at a high velocity, and is suitably used for a tube for a radiator or heater and for a pipe connected to heat exchangers.
In order to achieve the above object, the aluminum alloy clad material for heat exchangers exhibiting excellent erosion-corrosion resistance according to the present invention comprises a sacrificial anode material clad on one side of a core material, wherein the core material comprising an Al—Mn alloy and the sacrificial anode material comprising an aluminum alloy containing 3.0-12.0% of Si as an essential alloy component. Features of the aluminum alloy clad material of the present invention which comprises an aluminum alloy clad sheet and an aluminum alloy clad pipe are listed below.
(1) The core material comprises an Al—Mn alloy and the sacrificial anode material comprises an aluminum alloy containing 3.0-12.0% of Si with the remaining portion consisting of Al and impurities.
(2) The core material comprises an Al—Mn alloy and the sacrificial anode material comprises an aluminum alloy containing 3.0-12.0% of Si and 1.0-10.0% of Zn with the remaining portion consisting of Al and impurities.
(3) The core material comprises an Al—Mn alloy and the sacrificial anode material comprises an aluminum alloy containing 3.0-12.0% of Si and 0.15-1.2% of Fe with the remaining portion consisting of Al and impurities.
(4) The core material comprises an Al—Mn alloy and t
Hasegawa Yoshiharu
Ikeda Hiroshi
Kato Hisao
Miyachi Haruhiko
Shoji Yoshifusa
Denso Corporation
Flynn ,Thiel, Boutell & Tanis, P.C.
Koehler Robert R.
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