Lead free copper alloy and use of the lead free copper alloy

Abstract

The invention relates to a lead-free copper alloy comprising: 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 to less than 0.30 wt.% of Sn, remainder: Zn and unavoidable impurities.

Description

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

[0002] Copper alloys containing tin and aluminum are known according to the state of the art. Zr is necessarily added to these alloys for grain refinement. 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] German patent DE 103 08 778 B3 discloses a lead-free copper alloy suitable for use in drinking water and sanitary installations. The known copper alloy necessarily contains iron and / or cobalt as well as nickel and manganese.

[0004] A similar alloy is 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 lead-free copper alloys in which the tin content is at least 0.3 wt.%. The aluminum content is at least 0.1%. EP 2 634 275 A1 and CN 105603250 A disclose copper alloys.

[0006] The document "Acceptance of Metallic Materials Used for Products in Contact with Drinking Water", 5th Revision of "Procedure for the acceptance of metallic materials for PDW", 07.03.2016, adopted by the Joint Administrative Committee of France, Germany, the Netherlands and the United Kingdom, lists metallic materials that are approved for products in contact with drinking water in all four countries. Among them is the alloy CW724R (CuZn21Si3P), which contains copper and zinc as well as silicon and phosphorus.

[0007] The aforementioned lead-free alloys do not always form a sufficiently corrosion-inhibiting protective or oxide layer in practical use when in contact with drinking water. As a result, undesirable corrosion occurs due to the selective leaching of zinc from the alloy (so-called "dezincification").

[0008] The object of the invention is to overcome the disadvantages of the prior art. In particular, a lead-free copper alloy is to be provided whose corrosion resistance is improved, especially when used in drinking water applications.

[0009] This problem is solved by the features of claims 1 and 7.

[0010] Suitable embodiments of the invention result from the features of the dependent patent claims.

[0011] According to the invention, a lead-free copper alloy with a kappa phase content of at most 25 wt.% is proposed, comprising 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 to less than 0.30 wt.% of Sn, 0.01 to less than 0.1 wt.% of Al, remainder: Zn and unavoidable impurities.

[0012] The proposed lead-free copper alloy is characterized by improved corrosion resistance, particularly in contact with drinking water. This improved corrosion resistance is attributed to the formation of a protective oxide layer with enhanced adhesion. Surprisingly, this improved adhesion is achieved even with a tin content of less than 0.30 wt.%. Furthermore, it was found that the corrosion resistance can be increased by adding an even more surprising amount of aluminum, less than 0.1 wt.%.

[0013] The copper content is preferably 73.3 to 76.8 wt.%.

[0014] The copper alloy according to the invention comprises 0.01 to less than 0.1 wt.% Al. The proposed addition of Al improves the adhesion of the top layer.

[0015] In a further embodiment, the Si content is 2.40 to 2.90 wt.%, preferably 2.60 to 2.80 wt.%, and advantageously 2.60 to 2.78 wt.%. The proposed addition of Si helps to reduce the kappa phase to a maximum of 25 wt.%. It has been observed that the reduction in the kappa phase content also contributes to improved corrosion resistance.

[0016] The proportion of kappa phase is at most 25 wt.%, in particular 5 to 20 wt.%.

[0017] In a further embodiment, the proportion of aluminum is advantageously 0.01 to 0.05 wt.%. Furthermore, the proportion of phosphorus can be 0.08 to 0.10 wt.%. The proposed proportions enable the production of a particularly corrosion-resistant alloy.

[0018] The proposed lead-free copper alloy is particularly suitable for the manufacture of installation components for the drinking water sector, for example for the manufacture of fittings, valves, pipes, etc.

[0019] Exemplary embodiments of the invention are explained in more detail below based on test results.

[0020] Table 1 shows the composition of experimental alloys. Table 1 Alloy No. Alloying elements (wt.%) Cu Si P Sn Al 2737 76,43 3,35 0,091 0,003 0,002 2838 76,42 3,02 0,091 0,003 0,002 2839 76,45 2,72 0,091 0,003 0,001 2840 75,99 2,73 0,093 0,003 0,001 2841 76,44 2,75 0,052 0,002 0,001 2842 76,46 2,71 0,09 0,103 0,001 2843 76,52 2,71 0,093 0,287 0,001 2845 76,33 3,1 0,092 0,019 0 2846 76,16 3,4 0,048 0,005 0 2858 76,6 2,61 0,095 0,288 0,042

[0021] To produce the experimental alloys listed in Table 1, test specimens were prepared as follows: A melt formed from the alloying elements was poured into sand molds with a diameter of 40 mm at a temperature of 1020 °C to 1050 °C. The solidified specimens were then turned to a diameter of 24 mm. Next, the specimens were reduced to a diameter of 8 mm by simulated extrusion at a temperature of 700 °C. Finally, the specimens were annealed at 550 °C to 580 °C for 2 hours and then cooled in air.

[0022] In the table, alloy 2858 corresponds to an alloy according to the invention. The other alloys are comparative alloys.

[0023] Table 2 shows results of microstructure analyses. Table 2 Alloy No. Alloying elements structure Cu Si P Sn Al Kappa-MK Gamma-MK 2737 76,43 3,35 0,091 0,003 0,002 44% 1% 2838 76,42 3,02 0,091 0,003 0,002 31% 1% 2839 76,45 2,72 0,091 0,003 0,001 22% 1% 2840 75,99 2,73 0,093 0,003 0,001 24% 1% 2841 76,44 2,75 0,052 0,002 0,001 19% <1% 2842 76,46 2,71 0,09 0,103 0,001 15% 1% 2843 76,52 2,71 0,093 0,287 0,001 16% 1% 2845 76,33 3,1 0,092 0,019 0 26% <1% 2846 76,16 3,4 0,048 0,005 0 42% <1% 2858 76,6 2,61 0,095 0,288 0,042 10% <1%

[0024] Alloys Nos. 2842, 2843 and 2858 are characterized by a low content of kappa phase (= kappa-MK) of 10 to 16 wt.%.

[0025] The single figure shows the maximum depth of dezincification [µm] for the three alloys Nos. 2842, 2843, and 2858 in comparison to alloy No. 2846 (prior art). The "maximum depth of dezincification" refers to the depth to which leaching of zinc was detectable according to the following test protocol.

[0026] The samples were sawn. The sawn surface was exposed to drinking water for a period of 8 weeks. The drinking water was changed twice a week. The hardness of the drinking water was adjusted to 25°dH by adding NaCl and MgSO₄. The chloride content was 250 mg / l, and the sulfate content was also 250 mg / l. The exposure test was conducted under room conditions.

[0027] To determine the depth of dezincification, the sample was cut perpendicular to the surface, polished, and then optically analyzed using a reflected-light microscope. The depth of dezincification was recognizable by the characteristic color of the zinc-free copper sponge.

[0028] The addition of aluminum leads to increased oxide formation. Surprisingly, even small amounts of aluminum (from 0.04 wt.%) show firmly adhering oxide layers in a scale test (annealing at 800 °C) compared to aluminum-free samples, where the oxide layer flakes off easily. The oxide is generally considered to have a protective effect. The better the oxide adheres, the better the protective effect.

[0029] As from Fig. 1 As can be seen, alloys Nos. 2842, 2843 and 2858 exhibit a drastically reduced maximum depth of dezincification compared to alloy No. 2846 (prior art). In particular, no dezincification could be observed in alloy No. 2843 according to the invention.

[0030] The alloy according to the invention is characterized by a drastically improved corrosion resistance when in contact with drinking water.

Claims

1. Lead-free copper alloy having a kappa phase proportion of at most 25% by weight comprising: 70.0% to 83.0% by weight of Cu, 2.0% to 2.9% by weight of Si, 0.05% to 0.10% by weight of P, 0.01% to less than 0.30% by weight of Sn, 0.01% to less than 0.1% by weight of Al, balance: Zn and unavoidable impurities.

2. Lead-free copper alloy according to Claim 1, wherein the proportion of Cu is 73.3% to 76.8% by weight.

3. Lead-free copper alloy according to any of the preceding claims, wherein the proportion of Si is 2.40% to 2.90% by weight.

4. Lead-free copper alloy according to any of the preceding claims, wherein the proportion of Si is 2.60% to 2.80% by weight, preferably 2.60% to 2.78% by weight.

5. Lead-free copper alloy according to any of the preceding claims, wherein the proportion of Al is 0.01% to 0.05% by weight.

6. Lead-free copper alloy according to any of the preceding claims, wherein the proportion of P is 0.08% to 0.10% by weight.

7. Use of the lead-free copper alloy according to any of the preceding claims for production of installation components for the potable water sector.

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