Lead-free copper alloys and the use of lead-free copper alloys

Abstract

To provide a lead-free copper alloy whose corrosion resistance is improved for use in the field of service water.SOLUTION: A lead-free copper alloy contains 70.0 to 83.0 wt.% of Cu, 2.0 to 2.9 wt.% of Si, 0.05 to 0.10 wt.% of P, 0.01 wt.% to less than 0.30 wt.% of Sn, and a balance of Zn and unavoidable impurities.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a lead-free copper alloy.

Background Art

[0002] Copper alloys containing Sn and Al are known from the prior art. Furthermore, in order to achieve grain refinement, these necessarily contain Zr alloyed therein. Such copper alloys are described, for example, in EP 1 777 305 B1, EP 1 502 964 B1 and EP 1 777 308 B1.

[0003] DE 103 08 778 B3 discloses a lead-free copper alloy that can be used in the fields of mains water and sanitary equipment. Known copper alloys necessarily contain Fe and / or Co, and furthermore Ni and Mn.

[0004] Similar alloys are known from EP 1 600 515 A2.

[0005] EP 1 600 516 A2, EP 1 559 802 A1, EP 1 600 517 A2, EP 1 045 041 A1 and EP 1 508 626 A1 each disclose a lead-free copper alloy in which the Sn content is at least 0.3% by weight. The Al content is at least 0.1%.

[0006] In actual use, the above-described lead-free alloys do not necessarily form a coating or oxide film that is sufficiently corrosion-resistant upon contact with mains water. As a result, undesirable corrosion occurs due to the selective leaching of Zn from the alloy (known as "dezincification").

Summary of the Invention

Problems to be Solved by the Invention

[0007] The objective of this invention is to overcome the disadvantages of the prior art. In particular, the invention provides a lead-free copper alloy with improved corrosion resistance when used in the tap water sector. [Means for solving the problem]

[0008] This objective is achieved by the features of claims 1 and 9. Advantageous embodiments of the present invention arise from the features of the dependent claims. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 shows the maximum dezincification depth (μm) of three alloys No. 2842, 2843, and 2858 of the present invention, compared with alloy No. 2846 (prior art). [Modes for carrying out the invention]

[0010] This invention proposes a lead-free copper alloy containing 70.0 to 83.0 wt% Cu, 2.0 to 2.9 wt% Si, 0.05 to 0.10 wt% P, 0.01 wt% to <0.30 wt% Sn, the remainder being Zn and unavoidable impurities.

[0011] The proposed lead-free copper alloy exhibits improved corrosion resistance, particularly in contact with tap water. This improved corrosion resistance is attributed to the formation of a more adhesive coating or oxide film. Remarkably, this improved adhesion is achieved even with a Sn content of less than 0.30 wt%. Furthermore, it was found that corrosion resistance could be improved even with the addition of less than 0.1 wt% Al.

[0012] The Cu content is advantageously between 73.3 and 76.8% by weight.

[0013] In an advantageous embodiment, the copper alloy of the present invention contains 0.01% to <0.1% by weight of Al. The proposed addition of Al improves the adhesion of the coating layer.

[0014] In further embodiments, the proportion of Si is 2.40–2.90% by weight, preferably 2.60–2.80% by weight, and advantageously 2.60–2.78% by weight. The proposed addition of Si contributes to reducing the kappa phase content to 25% by weight or less. It has been observed that reducing the proportion of the kappa phase contributes to improved corrosion resistance. The proportion of the kappa phase is preferably 25% by weight or less, particularly preferably 5–20% by weight.

[0015] In further embodiments, the proportion of Al is advantageously 0.01 to 0.05% by weight. Furthermore, the proportion of P can be 0.08 to 0.10% by weight. The proposed proportions make it possible to produce alloys with particularly excellent corrosion resistance.

[0016] The proposed lead-free copper alloy is particularly suitable for the manufacture of installation components for the mains water sector, such as fittings, valves, and pipes. [Examples]

[0017] Examples of the present invention will be described in more detail below, along with experimental results.

[0018] Table 1 shows the composition of the experimental alloys.

[0019] [Table 1]

[0020] To produce the experimental alloys listed in Table 1, test specimens were prepared as follows.

[0021] The melt formed by alloying elements was poured into a sand mold with a diameter of 40 mm at a temperature of 1020 °C to 1050 °C. Subsequently, the solidified test piece was made to have a diameter of 24 mm. Then, through extrusion simulation at a temperature of 700 °C, the diameter of the test piece was reduced to 8 mm. Finally, the test piece was heat-treated at 550 °C to 580 °C for 2 hours and then cooled in air.

[0022] In Table 1, Alloy Nos. 2842, 2843, and 2858 correspond to the alloys of the present invention. The remaining alloys are alloys of the comparative examples.

[0023] Table 2 shows the results of the fine structure analysis.

[0024] [Table 2]

[0025] The alloys of the present invention, Alloy Nos. 2842, 2843, and 2858, have a low content of kappa phase (=kappa MK) of 10 to 16% by weight.

[0026] One figure shows the maximum dezincification depth (μm) of three alloys of the present invention, Alloy Nos. 2842, 2843, and 2858, compared with Alloy No. 2846 (prior art). The "maximum dezincification depth" is the maximum depth at which Zn leaching was detectable by the following experimental procedure.

[0027] The test piece was cut. The cut surface was contacted with tap water for 8 weeks. The tap water was changed twice a week. The hardness of the tap water was set to a value of 25 °dH by adding NaCl and MgSO4. The chloride content was 250 mg / l, and the sulfate content was also 250 mg / l. The leaching experiment was conducted under room temperature conditions.

[0028] To measure the dezincification depth, the test piece was cut perpendicular to the surface, polished, and then optically analyzed with a reflected optical microscope. The dezincification depth could be examined from the characteristic color of zinc-free copper sponge.

[0029] The addition of aluminum increases oxide formation. Even small amounts of aluminum (0.04% by weight or more) surprisingly result in a firmly adhering oxide film in scale tests (heat treatment at 800°C) compared to aluminum-free specimens (in which case the oxide film peels off significantly). The protective effect is usually attributed to this oxide. The better the adhesion of the oxide, the better the protective effect.

[0030] As can be seen from Figure 1, alloys No. 2842, 2843, and 2858 of the present invention have a maximum depth with significantly reduced dezincification compared to alloy No. 2846 (prior art). In particular, no dezincification was observed in alloy No. 2843 of the present invention.

[0031] The alloy of the present invention exhibits significantly improved corrosion resistance upon contact with tap water.

Claims

1. 70.0 to 83.0 mass% Cu, 2.0 to 2.9 mass% Si, 0.05 to 0.10 mass% of P, Sn in amounts from 0.01 mass% to <0.30 mass%, Remainder: Zn and inevitable impurities A lead-free copper alloy consisting of [the following components].

2. 70.0 to 83.0% by mass of Cu, 2.0 to 2.9 mass% Si, 0.05 to 0.10 mass% of P, Sn in amounts from 0.01 mass% to <0.30 mass%, Al in a concentration of 0.01% by mass to <0.1% by mass, Remainder: Zn and inevitable impurities A lead-free copper alloy consisting of the following components.

3. The lead-free copper alloy according to claim 2, wherein the proportion of Al is 0.01 to 0.05 mass%.

4. A lead-free alloy according to any one of claims 1 to 3, wherein the proportion of Cu is 73.3 to 76.8% by mass.

5. A lead-free copper alloy according to any one of claims 1 to 4, wherein the proportion of Si is 2.40 to 2.90 mass%.

6. A lead-free copper alloy according to any one of claims 1 to 4, wherein the proportion of Si is 2.60 to 2.80 mass%.

7. The lead-free copper alloy according to any one of claims 1 to 4, wherein the proportion of Si is 2.60 to 2.78% by mass.

8. A lead-free copper alloy according to any one of claims 1 to 7, wherein the proportion of the kappa phase is 25% by mass or less.

9. A lead-free copper alloy according to any one of claims 1 to 8, wherein the proportion of P is 0.08 to 0.10 mass%.

10. Use of the lead-free copper alloy according to any one of claims 1 to 9 for manufacturing mounting components in the tap water sector.

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