WO2004087974A1

WO2004087974A1 - Machinable copper alloy

Info

Publication number: WO2004087974A1
Application number: PCT/FI2004/000197
Authority: WO
Inventors: Kalle Härkki; Tuomas Renfors; Timo VÄLIMÄKI
Original assignee: Outokumpu Oyj
Current assignee: Outokumpu Oyj
Priority date: 2003-04-03
Filing date: 2004-04-01
Publication date: 2004-10-14
Anticipated expiration: 2005-10-03
Also published as: FI20030506L; FI20030506A0; FI117289B; TW200422411A

Abstract

The invention relates to a machinable oxygen-free copper alloy containing oxygen not more than 10 ppm of the alloy weight. As the only alloy ingredient, the alloy contains sulfur for 50 - 300 ppm of the alloy weight. In this way, machinability is improved, while the electroconductivity still remains good.

Description

MACHINABLE COPPER ALLOY

Field of the invention

The invention relates to an oxygen-free copper alloy, in which there is alloyed material that improves machinability, particularly punchability. The alloy is particularly suited to be used in targets where both a good electroconductivity and a good machinability are required.

Description of the prior art

The oxygen content of the most generally used copper quality, so-called ETP copper (electrolytic tough pitch) is typically 200 - 400 ppm of the copper weight. Oxygen is naturally bound in copper in a regular manufacturing process. The oxygen content can also be kept on a desired level intentionally, because oxygen bounds harmful substances to less harmful oxides. The oxide particles also increase brittleness, which improves for instance punchability.

Generally the electroconductivity of copper is always the higher, the purer the copper is. The thermal conductivity of copper is proportional to its electroconductivity. Particularly for improving electroconductivity, machinability and weldability, there is manufactured so-called oxygen-free copper with an oxygen content not higher than 10 ppm. In the manufacturing of oxygen-free copper, oxygen is prevented from getting into contact with molten copper by using a protective, reducing layer on top of the melt (for example graphite), by using protective gas (for example nitrogen) or by using a vacuum.

However, oxygen-free copper is high-tensile by nature, which in some cases results in machination problems, for example in punching.

In the publication JP-A-62253743, there is suggested an oxygen-free copper particularly for machination, which alloy contains a total quantity of 0.02 - 1.0% of at least two of the following materials: sulfur, selenium and tellurium. In the publication JP-A-06002058, there is suggested an oxygen-free copper alloy with 0.0006 - 0.0015% sulfur for preventing grain growth.

Summary of the invention

We have now invented an oxygen-free copper according to claim 1. Preferred embodiments of the invention are set forth in the other claims.

According to the invention, in the oxygen-free copper there is alloyed, as the only alloy ingredient, sulfur for 50 - 300 ppm of the alloy weight. Thus the machinability is improved, while the electroconductivity still remains good.

The alloy is suited to be used particularly in products where there is required both good electroconductivity or thermal conductivity and good machinability. Such products are for instance various electroconductive components manufactured by punching.

Detailed description of the invention

The sulfur content of an oxygen-free copper according to the invention is 50 - 300 ppm, preferably 100 - 200 ppm. The oxygen content of the alloy is not higher than 10 ppm, preferably not higher than 5 ppm, such as 1 - 3 ppm.

By means of the sulfur alloying according to the invention, the machinability, and particularly the punchability, of oxygen-free copper is remarkably improved. When the machinability is of the same order as with ETP copper, the replacing of ETP copper by the copper according to the invention becomes possible.

In comparison with ETP copper, oxygen-free copper also has the advantage that there is no risk of hydrogen brittleness. Thus oxygen-free copper is better suited to be processed at high temperatures, for instance by soldering and welding.

The brittleness-increasing effect of sulfur is based on its occurrence as separate particles in the copper matrix. Particle size has a remarkable significance, particularly in punchability behavior: the larger the particles, the better is the punchability. Particle size can be affected by the cooling rate of the cast billet, and by separate thermal treatments carried out at a high temperature.

The alloy can be manufactured by similar manufacturing techniques as other qualities of oxygen-free copper, for example in slab or rod casting, either as horizontal or vertical casting. In a suitable step of the process, for instance into the casting furnace, there is added a required amount of sulfur. By applying a slab/rod/hot rolling/hot extrusion method, there is achieved a larger size for the sulfur particles than with a vertical casting - hot extrusion method.

The alloy can be processed for instance into strip with a thickness of for example 0.2 - 12 mm. Various products can be made of this kind of strip, for instance by punching. Among said products are for example many electroconductive and heat conductive components. For instance air- conditioning holes (such as in cooling fins) or fastening holes can be made by punching. This kind of strip can be manufactured particularly by using the slab casting and hot rolling route.

Another feasible manufacturing route is vertical casting - continuous hot extrusion. In this way, there can be manufactured for instance flat bar or other profile with a thickness range within 4 - 12 mm.

The sulfur content of copper does not weaken for instance weldability properties. Neither does sulfur cause problems for example in recirculation. Example

There were manufactured oxygen-free copper alloys, in which there were alloyed sulfur 50, 100, 150, 200, 250 and 300 ppm. The materials were manufactured by rod casting in a vacuum furnace, they were hot extruded into the measure 39.9^*7,2 mm and drawn to the measure 38.96*6,17 mm (red. 16 %). The employed reference material was drawn flat bar, taken from production, with the measures 6^*40 mm. Its degree of deformation was roughly the same as that of the test materials. In these materials, there were punched elongate holes (about 3*25 mm) with the same tool. In addition to punchability, the test materials were tested for electroconductivity and mechanical properties.

As the magnitude describing punchability, there can be used the share of the fractured zone of the whole cutting surface. With high-tensile materials, the share of the polished zone is relatively larger than with brittle materials. The final result is also remarkably affected by the die clearance, i.e. the distance between the die cushion and the cutting surfaces. The more tensile the material is, the smaller the clearance that must be used in order to reach the same final result. However, the smaller the cutting clearance is, the more intensive is the wearing of the tool. When increasing the cutting clearance, the share of the fracture of the whole cutting surface increases.

In the experiments, punchability was studied with die clearances of 0.55 and 0.85 mm, when it was detected that with larger or smaller values, the obtained results were too uneven. The punching tool used in the experiments was levelheaded, and it had a 1 mm back draft. Three holes were punched by each combination of material and punching parameter.

The test results are given in the attached table.

When observing the punching result, it was found out that with sulfur-bearing samples, the fractured zone was fairly even in comparison with non-alloyed copper.

In the table below, there are given the measured mechanical properties of the samples, as well as their electroconductivity .

Part of the samples were also subjected to a bending test that was carried out without problems.

Claims

1. A machinable oxygen-free copper alloy, containing oxygen not more than 10 ppm of the alloy weight, characterized in that the alloy contains, as the only alloy ingredient, sulfur for 50 - 300 ppm of the alloy weight.

2. A copper alloy according to claim 1 , containing sulfur for 100 - 200 ppm.

3. A punchable copper alloy according to claim 1 or 2.

4. A copper alloy according to any of the preceding claims, which copper alloy is formed into a strip.

5. A copper alloy according to claim 4, where the thickness of the strip is 0.2 - 12 mm.

6. A copper alloy according to claim 4 or 5, which is manufactured by using the slab casting - hot rolling route.

7. A method for manufacturing a machinable oxygen-free copper alloy, said alloy containing oxygen not more than 10 ppm of the alloy weight, characterized in that in the alloy, there is alloyed, as the only alloy ingredient, sulfur for 50 - 300 ppm of the alloy weight.

8. A method according to claim 7, where the alloy is manufactured by using the slab casting - hot rolling route, the odr casting - hot extrusion route or the vertical casting - continuous hot extrusion route.

9. The use of a copper alloy according to any of the claims 1 - 6 or manufactured according to claims 7 or 8 in a product that is machined by punching.