Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
1999-11-02
2001-01-30
Thibodeau, Paul (Department: 1773)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S405000, C427S433000, C205S222000, C205S224000, C205S225000, C428S647000
Reexamination Certificate
active
06180174
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to copper alloys and a process for the production thereof. The term “copper alloys” herein used includes in the strict sense both copper and copper alloys. However, either one of them will simply be referred to as this term hereunder. In particular, the invention relates to copper alloys that can provide surfaces having improved characteristics suitable for the production of various types of electrical parts, such as, a surface exhibiting decreased friction during insertion and drawing, for example, a surface of a multi-pin connector used for electric wiring in an automobile production; a surface of a charging-socket of an electric automobile which is used repeatedly a great number of times in insertion and drawing; a surface of a brush which is used in contact with a rotating body such as an electric motor and therefore is required to be highly resistant to abrasion; and a surface of a battery terminal which is also required to be highly resistant to abrasion and corrosion. The invention also relates to a process for the production of copper alloys referred to above.
2. Background Information
With the recent development of the electronics industry, electric wiring in various machines is becoming more and more complicated and highly integrated, and this has caused use of connectors having an increased number of pins. Conventional connectors having Sn-plated surfaces have encountered a problem in that the practical use thereof is becoming more and more difficult because of the increased friction at the times of insertion and drawing.
Currently available electric automobiles require charging at least once a day. Thus, it is necessary that a charging-socket is highly resistant to abrasion. In addition, since a large amount of electric current such as 10A or more flows in sockets and therefore a large amount of heat is generated, a new problem that Sn-plated surfaces of sockets obtained by a conventional method cannot withstand the delamination of the plated surface has occurred.
A deeper understanding has been acquired with respect to the fact that the above-stated problems cannot be solved by conventional surface treatment methods. A method of the kind of the present invention was also among the conventional methods, which comprises the steps of applying heat treatment to a copper alloy and subsequently causing heat diffusion in the alloy. However, the conventional method was no more than the method for only preventing the separation or peeling off, due to the influence of working or heat, of the surface treated layer from the alloy body by making use of the diffusion between the surface treated layer and the matrix. For this reason, the stated problems could not be solved by said prior art method.
SUMMARY OF THE INVENTION
The present invention has been accomplished to solve the above-mentioned problems, and provides a copper alloy and a process for the production thereof. The process of the invention comprises the steps of coating the surface of a copper alloy material with Sn or an Sn-alloy coating followed by applying heat treatment to the coated surface, thereby forming in the surface treated layer on said material a very hard coating containing Cu—Sn system intermetallic compounds (Cu
3
Sn, Cu
4
Sn etc.) and Cu—Sn—Zn system lntermetallic compounds. By doing this, the present invention provides a copper alloy having a surface which is suitable when used as a connector or as a charging-socket of an electric automobile because of its having a low coefficient of friction and high resistance to abrasion.
The present invention has been accomplished based on the finding that the surface hardness can be increased greatly by having a specified thickness of an Sn layer coated on a Cu alloy having a specified composition and also utilizing specified heat treating conditions. This enables formation of Cu—Sn system intermetallic compounds (Cu
3
Sn, Cu
4
Sn etc.) and Cu—Sn—Zn system intermetallic compounds, whereby the Vickers hardness (Hv) of the coated surface can be increased to 300 or more, preferably 400 or more, which is remarkably higher than the hardness of Sn-plated surfaces (60 to 120) or that of matrix (80 to 250); thus the invention provides a copper alloy and a process for the production of the alloy which has electrical and working characteristics suitable for making connectors of an automobile and charging-sockets of an electric automobile, having a surface with a low coefficient of friction and superior resistance to abrasion.
In one aspect, the invention provides a coated copper alloy having a surface coating of Sn wherein said copper alloy consists essentially of 1-41 wt % Zn with the balance being Cu and incidental impurities, said surface coating is formed by surface treating said copper alloy with Sn, followed by heat treating the Sn coated copper alloy to cause heat diffusion so as to form a surface coating consisting essentially of Cu and Sn, said surface coating extending to the depth which includes at least the interface between said Sn layer and said copper alloy.
In another aspect, the invention provides a coated copper alloy having a surface coating of Sn wherein said copper alloy consists essentially of 1-41 wt % Zn, 0.01-9 wt % in total of one or two or more elements selected from the group consisting of Fe, Ni, Sn, Al, Co, Ti, Cr, Mg, Si and P with the balance being Cu and incidental impurities, said Sn coating is formed by surface treating said copper alloy with Sn, followed by heat treating the Sn coated copper alloy to cause heat diffusion so as to form a surface coating consisting essentially of Cu and Sn, said surface coating extending to the depth which includes at least the interface between said Sn layer and said copper alloy.
The surface coating has a Vickers hardness of at least 300 and preferably of more than 400.
The invention also provides electrical parts made from the coated Cu alloys of the present invention.
The invention further provides electrical connector terminals made from the coated Cu alloys of the present invention.
The invention also provides a process for the production of a coated Cu alloy comprising the steps of coating with Sn the surface of a Cu alloy consisting essentially of 1-41 wt % Zn with the balance being Cu and incidental impurities, and applying heat treatment to the Sn coated Cu alloy at a temperature between 100 and 450° C., preferably between 200 and 400° C., for 0.5 to 24 hours, preferably for 1 to 3 hours.
The invention further provides a process for the production of a coated Cu alloy comprising the steps of coating with Sn the surface of a Cu alloy consisting essentially of 1-41 wt % Zn and 0.01-9 wt % in total of one or two or more elements selected from the group consisting of Fe, Ni, Sn, Al, Co, Ti, Cr, Mg, Si and P, with the balance being Cu and incidental impurities, and applying heat treatment to the Sn coated Cu alloy at a temperature between 100 and 450° C., preferably between 200 and 400° C., for 0.5 to 24 hours, preferably for 1 to 3 hours.
The thickness of the Sn coating of the above-mentioned coated Cu alloys should be in the range of 0.5-10 &mgr;m, preferably 1-5 &mgr;m.
The surface roughness (Rmax) of the above-mentioned coated Cu alloys should be 3 &mgr;m or less.
The heat treatment in the process of the invention can also be effected stepwise at two or more different temperatures, so long as each treating temperature is within the specified range and total treating time is within the specified period of time.
REFERENCES:
patent: 3892637 (1975-07-01), Polti
patent: 4348263 (1982-09-01), Draper et al.
patent: 5334814 (1994-08-01), Nosetani et al.
Endo Takayoshi
Hana Yoshitake
Sugawara Akira
Sugiyama Osamu
Dowa Mining Co. Ltd.
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Rickman Holly
Thibodeau Paul
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