Metal treatment – Stock – Aluminum base
Reexamination Certificate
2001-09-14
2003-10-28
Wyszomierski, George (Department: 1742)
Metal treatment
Stock
Aluminum base
C420S548000, C420S551000, C420S553000
Reexamination Certificate
active
06638376
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an aluminum alloy piping material. More particularly, the present invention relates to an aluminum alloy piping material having an excellent corrosion resistance and workability, which is suitably used for pipes connecting automotive radiators and heaters or pipes connecting evaporators, condensers, and compressors.
2. Description of Background Art
Pipes used for passages connecting automotive radiators and heaters or passages connecting evaporators, condensers, and compressors are provided with a bulge at the pipe ends, and connected to radiators, heaters, evaporators, condensers, or compressors. Pipes connected to radiators or the like are connected to a rubber hose and fastened using a metal band. As the piping material, a single pipe consisting of an Al—Mn alloy such as a 3003 alloy, and a two-layered or three-layered clad pipe consisting of an Al—Mn alloy as a core material and an Al—Zn alloy sacrificial anode material such as a 7072 alloy clad on the core material have conventionally been used.
In the case where the Al—Mn alloy piping material is used under a severe environment, pitting corrosion or intergranular corrosion tends to occur. When the Al—Mn alloy piping material is connected to a rubber hose, crevice corrosion occurs in the piping material at the inner side of the rubber hose, specifically, the outer side of the piping material. Use of a clad pipe prevents the occurrence of pitting corrosion or crevice corrosion. However, this significantly increases costs.
In order to solve the above problem, Japanese Patent Application Laid-open No. 4-285139 proposes a piping material exhibiting improved crevice corrosion resistance, in which Cu and Ti are added to an Al—Mn alloy and the Fe content and the Si content are limited within a specific range. This piping material has good properties under various use conditions. However, this piping material may exhibit insufficient workability during bulge formation of the pipe ends when used as a pipe. Moreover, this piping material has a problem with corrosion resistance when allowed to stand under a severe corrosive environment.
SUMMARY OF THE INVENTION
The present inventors have examined the above problems of the Al—Mn alloy piping material relating to a decrease in workability and corrosion resistance. As a result, the present inventors have found that a decrease in the corrosion resistance is caused by microgalvanic corrosion occurring between an alloy matrix and various intermetallic compounds present in the matrix. The present inventors have also found that workability at the pipe ends is affected by the distribution state of the intermetallic compounds.
The present invention has been achieved as a result of further experiments and studies on the Al—Mn alloy piping material based on the above findings. Accordingly, an object of the present invention is to provide an aluminum alloy piping material exhibiting good corrosion resistance even under a severe corrosive environment and having an excellent workability, such as bulge formation capability at the pipe ends.
One aspect of the present invention provides an aluminum alloy piping material having an excellent corrosion resistance and workability, comprising an aluminum alloy which comprises 0.3-1.5% of Mn, 0.20% or less of Cu, 0.06-0.30% of Ti, 0.01-0.20% of Fe, and 0.01-0.20% of Si, with the balance consisting of Al and impurities, wherein, among Si compounds, Fe compounds, and Mn compounds present in the matrix, the number of compounds with a particle diameter of 0.5 &mgr;m or more is 2×10
4
or less per mm
2
.
In this aluminum alloy piping material having an excellent corrosion resistance and workability, the aluminum alloy may further comprise 0.4% or less of Mg.
In the above aluminum alloy piping material having an excellent corrosion resistance and workability, the aluminum alloy may further comprise at least one of 0.01-0.2% of Cr and 0.01-0.2% of Zr.
In the above aluminum alloy piping material having an excellent corrosion resistance and workability, the Cu content in the aluminum alloy may be 0.05-0.10%.
In the above aluminum alloy piping material having an excellent corrosion resistance and workability, the Fe content in the aluminum alloy may be 0.01-0.09%.
In the above aluminum alloy piping material having an excellent corrosion resistance and workability, the number of compounds with a particle diameter of 0.5 pm or more may be from 1×20
3
to 2×10
4
per mm
2
.
In the above aluminum alloy piping material having an excellent corrosion resistance and workability, the tensile strength of the softened material (O material) may be 130 MPa or less.
DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
The effects of alloy components of an aluminum alloy piping material having an excellent corrosion resistance and workability of the present invention, and reasons for the limitations of the aluminum alloy are described below. Mn increases the strength and improves corrosion resistance, in particular, pitting corrosion resistance. The Mn content is preferably 0.3-1.5%. If the Mn content is less than 0.3%, the effect may be insufficient. If the Mn content exceeds 1.5%, a large number of Mn compound particles may be formed, whereby the corrosion resistance may decrease. The Mn content is still more preferably from 0.8% or more to less than 1.2%.
Cu improves the strength of the alloy. The Cu content is preferably 0.20% or less. If the Cu content exceeds 0.20% corrosion resistance may decrease. The Cu content is still more preferably 0.05-0.10%.
Ti is separately distributed in a high-concentration area and a low-concentration area. These areas are alternately layered in the direction of the thickness. The low-concentration area is preferentially corroded rather than the high-concentration area, thereby forming corrosion layers. This prevents the corrosion from proceeding in the direction of the thickness, thereby improving pitting corrosion resistance, intergranular corrosion resistance, and crevice corrosion resistance of the material. The Ti content is preferably 0.06-0.30%. If the Ti content is less than 0.06%, the effect may be insufficient. If the Ti content exceeds 0.30%, giant compounds may be produced during casting, thereby decreasing workability. As a result, a sound piping material cannot be obtained. The Ti content is still more preferably 0.15-0.25%.
Fe decreases the grain size after extrusion or the grain size after drawing and annealing, thereby improving formability of the piping material. This prevents the occurrence of cracks or surface roughening during bulge formation or the like. The Fe content is preferably 0.01-0.20%. If the Fe content is less than 0.01%, the effect may be insufficient. If the Fe content exceeds 0.20%, a large number of Fe compound particles may be formed, whereby the corrosion resistance may decrease. The Fe content is still more preferably 0.01-0.09%.
Si decreases the grain size after extrusion or the grain size after drawing and annealing in the same manner as Fe, thereby improving formability of the piping material. This prevents the occurrence of cracks or surface roughening during bulge formation or the like. Moreover, Si forms Al—Mn—Si compounds and Al—Mn—Fe—Si compounds, thereby preventing the occurrence of penetration between tools and the material during bending, bulge formation, or the like. The Si content is preferably 0.01-0.20%. If the Si content is less than 0.01%, the effect may be insufficient. If the Si content exceeds 0.20%, a large number of Si compound particles may be formed, whereby the corrosion resistance may decrease. The Si content is still more preferably 0.01-0.10%.
Mg increases the strength and decreases the grain size. The Mg content is preferably 0.4% or less (but more than 0%). If the Mg content exceeds 0.4%, extrusion capability and corrosion resistance may decrease. The Mg content is still more preferably 0.20% or less.
Cr and Zr are separately distributed in a high-concentration
Fukuda Toshihiko
Hasegawa Yoshiharu
Koyama Takahiro
Miyachi Haruhiko
Shoji Yoshifusa
Combs-Morillo Janelle
Denso Corporation
Flynn ,Thiel, Boutell & Tanis, P.C.
Wyszomierski George
LandOfFree
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