Alloys or metallic compositions – Copper base – Nickel containing
Patent
1987-09-25
1989-05-16
Roy, Upendra
Alloys or metallic compositions
Copper base
Nickel containing
420485, 420488, C22C 901, C22C 906
Patent
active
048308250
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION:
1. Field of the Invention:
The present invention relates to a corrosion-resistant copper alloy which has excellent weather resistance, i.e, resistance to discoloration in the atmosphere and a long-lasting beautiful color tone close to gold, superior corrosion resistance, particularly, high resistance to corrosion by seawater, as well as high strength and excellent cold formability.
2. Description of the Related Art
In the production of marine propellers, tube sheets of heat exchangers in desalination plant, various kinds of valves, automative parts, oil-hydraulic parts, etc., a special aluminum bronze known as a corrosion-resistant copper alloy which has the following composition has heretofore been employed: above-described composition and in the following description "%" denotes "percent by weight"; this special aluminum bronze will hereinafter be referred to as a "conventional copper alloy").
Although the above-described conventional copper alloy has excellent corrosion resistance, particularly, excellent resistance to corrosion by seawater, and high strength, it suffers from the following problems. In use, the prior art copper alloy is formed into a casting having a predetermined configuration which is produced by casting the molten alloy using, for example, a permanent mold, or the ingot of the copper alloy which is formed by, for example, continuous casting, is subjected to hot forging or hot rolling to form casting or wrought predetermined configuration, and this material is then softened by annealing process in which it is maintained at 600.degree. to 800.degree. C. for 1 to 2 hours. Thus, the conventional copper alloy is made available for practical use in a condition wherein a large amount of crystallized phases such as crystallized Fe and also a large amount of precipitated phases such as intermetallic compounds containing Fe as a principal component and Fe oxides are dispersed in the .alpha.-phase which defines the matrix of the alloy structure. Accordingly, the conventional copper alloy suffers from inferior weather resistance due to the crystallized phases and the precipitated phases and therefore loses its color easily in the atmosphere and cannot maintain its own beautiful color tone which is close to gold over a long period of time. For this reason, it is impossible to make use of the beautiful golden tone of this alloy for Western tableware, vessels, fittings for buildings and decorative articles. In addition, the prior art disadvantageously has inferior cold formability.
Summary of the Invention
In view of the above-described circumstances, the present inventors made exhaustive studies with a view to imparting excellent weather resistance and cold formability to the above-described conventional copper alloy without degrading its superior properties, i.e., high strength and excellent resistance to corrosion by seawater. As a result, the present inventors have found that a copper alloy, which has a composition consisting essentially of: after being processed to a cast material or a hot- or cold-wrought material, is subjected to a heat treatment wherein it is quenched (water cooling or forced air cooling) from a temperature ranging from 800.degree. to 1000.degree. C. to obtain a substantially single-phase structure which consists essentially of .alpha.-phase, i.e., in which the number of crystallized phases and precipitated phases dispersed in the .alpha.-phase serving as the matrix is reduced to 50,000/mm.sup.2 or less, preferably 30,000/mm.sup.2 or less, has high strength and excellent resistance to corrosion by seawater, which properties are equivalent to those of the above-described conventional copper alloy, and yet has much superior weather resistance and consequently loses its color only slightly in the atmosphere and can maintain its beautiful golden tone over a long period of time, the alloy also having excellent cold formability.
The present invention has been accomplished on the basis of the above-described finding. The reason why the composition
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Goto Sachio
Hayashi Hiroshi
Kimura Tsutomu
Kobayashi Hideo
Yasumori Akira
Kusakabe Copastar Company
Mitsubishi Kinzoku Kabushiki Kaisha
Roy Upendra
Sachio Goto
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