Copper-zinc-molybdenum cast alloy, casting produced therefrom and method for producing such a copper-zinc-molybdenum cast alloy

Abstract

The invention relates to a copper-zinc-molybdenum casting alloy, a casting made therefrom, and a method for producing such a casting alloy.

Description

[0001] The invention relates to a copper-zinc-molybdenum casting alloy, a casting made therefrom, and a method for producing such a copper-zinc-molybdenum casting alloy.

[0002] Copper-zinc alloys, also known as brasses, are known in a variety of ways from the prior art and are used, for example, in the manufacture of electrical components and in bearing technology.

[0003] Such copper-zinc alloys often contain lead to improve manufacturability and machinability. For example, EP 0 621 346 A1 discloses a lead-containing copper-zinc alloy for the production of nickel-free consumer goods, such as eyeglass parts or jewelry components.

[0004] For health and environmental reasons, lead, being a toxic heavy metal, is increasingly undesirable as an alloying element. To replace lead, the addition of sulfur has been discussed, which can act as a chip breaker and thus facilitate machining.

[0005] For example, German patent DE 10 2020 106 999 A1 addresses the issue of copper-tin continuous casting alloys, stating that the addition of sulfur can improve castability because the copper and zinc sulfides formed by the sulfur accumulate in otherwise typically present micropores, thus sealing these cavities. Furthermore, it was discussed that copper sulfide can have a positive effect on the tribological properties.

[0006] However, the addition of sulfur to zinc-containing alloys creates a further conflict of objectives, as the zinc sulfide that forms can reduce strength and, due to the higher hardness, increase tool wear during machining.

[0007] The present invention is based on the objective of providing a copper-zinc casting alloy that can be produced and cast well and economically, and which is easily machinable after casting and has good tribological properties.

[0008] This problem is solved according to the invention by a casting alloy having the features of claim 1. This is a casting alloy consisting of: 1.5 - 38.5 wt.%, in particular 7.0 - 38.5 wt.%, zinc; 0.6 - 4.2 wt.% molybdenum; 0.4 - 3.1 wt.% sulfur; optionally up to 4.5 wt.%, in particular up to 4.0 wt.%, iron; optionally up to 5.5 wt.%, in particular up to 5.0 wt.%, silicon; optionally up to 7.5 wt.%, in particular up to 7.0 wt.%, aluminum; optionally up to 0.8 wt.% phosphorus, balance copper and unavoidable impurities. wherein, based on weight percent, the ratio of sulfur to molybdenum in the alloy is greater than 0.6, in particular greater than 0.65, and further in particular at least 0.66 (i.e., where the ratio of the mass fraction (in wt.%) of sulfur in the alloy to the mass fraction (in wt.%) of molybdenum in the alloy is greater than 0.6, in particular greater than 0.65, and further in particular at least 0.66), and wherein the total fraction of molybdenum and sulfur (i.e., the sum of the mass fraction (in wt.%) of molybdenum in the alloy and the mass fraction (in wt.%) of sulfur in the alloy) is more than 0.15 times the zinc fraction (i.e., the mass fraction (in wt.%) of zinc in the alloy). In this respect, the following condition applies to the mass fractions of molybdenum, sulfur, and zinc:

[0009] The proposed casting alloy is environmentally friendly, casts well, and exhibits good machinability and tribological properties in the cast state. It has been shown that the combination of molybdenum and sulfur can at least partially replace the properties of substituted lead while simultaneously overcoming the aforementioned conflict of objectives. Specifically, it was discovered within the scope of the invention that the combination of molybdenum and sulfur in the claimed mass fraction and mass ratio causes molybdenum disulfide (MoS₂) to precipitate during solidification, and that this molybdenum disulfide adheres to or even encapsulates the zinc sulfide that also precipitates. It has been shown that in this way the damaging effects of the zinc sulfide can be suppressed or at least significantly reduced.Furthermore, it was found that the addition of molybdenum increases the sulfur content in the melt and can also partially suppress or at least slow down unwanted evaporation of sulfur (e.g., in the form of ZnS). Finally, it was shown that the precipitated molybdenum disulfide, in addition to its function of coating zinc sulfide, can exhibit its well-known lubricating properties as a dry lubricant, which has a positive effect on the tribological properties.

[0010] The present invention relates to a casting alloy of the claimed composition in the molten state. Furthermore, the present invention relates to a casting alloy of the claimed composition in the cast and, in particular, the cooled state. In the cast alloy, sulfur and molybdenum are present, in particular at least partially, as MoS₂.

[0011] The casting alloy is in particular lead-free, i.e., that lead is not actively added as an alloying element and that any residual lead due to impurities is at most 0.10 wt.%, in particular at most 0.09 wt.%, in particular at most 0.08 wt.%, in particular at most 0.07 wt.%, in particular at most 0.06 wt.% and preferably at most 0.05 wt.%.

[0012] Preferably, the ratio of sulfur to molybdenum in the alloy is at most 2.5, more preferably at most 1.5, further preferably at most 1.0, and further preferably at most 0.8.

[0013] In particular, the ratio of sulfur to molybdenum in the alloy is between 0.6 and 2.5, preferably between 0.65 and 2.0, more preferably between 0.65 and 1.5, and even more preferably between 0.65 and 1.0. A ratio of sulfur to molybdenum in the alloy between 0.66 and 0.8 is particularly preferred.

[0014] Furthermore, it proves advantageous if the casting alloy contains 1.0 - 4.0 wt.%, 1.4 - 3.6 wt.%, more particularly 1.5 - 3.2 wt.%, more particularly 1.6 - 2.9 wt.%, more particularly 1.7 - 2.4 wt.%, more particularly 1.8 - 1.9 wt.% molybdenum.

[0015] Furthermore, it proves advantageous if the casting alloy contains 0.4 - 2.9 wt.%, in particular 0.5 - 2.7 wt.%, in particular 0.6 - 2.6 wt.%, in particular 0.9 - 2.4 wt.%, 1.2 - 2.2 wt.%, in particular 1.3 - 1.8 wt.%, in particular 1.4 - 1.6 wt.% sulfur.

[0016] A higher molybdenum / sulfur content contributes in particular to improved tribological properties.

[0017] With regard to the zinc content, it can be advantageous if the alloy contains 2.0–13.5 wt.%, in particular 7.0–9.0 wt.%, and more specifically 7.5–8.5 wt.%, zinc. In this respect, the alloy can contain at least 2.0 wt.%, in particular 7.0 wt.%, and more specifically 7.5 wt.% zinc, and preferably at most 13.5 wt.%, in particular at most 9.0 wt.%, and more specifically at most 8.5 wt.% zinc. In particular, the cast alloy can then contain 0.6–1.9 wt.%, in particular 1.0–1.8 wt.%, and more specifically 1.1–1.4 wt.% molybdenum, and 0.4–1.7 wt.%, in particular 0.5–1.5 wt.%, and more specifically 0.7–1.2 wt.% sulfur. A comparatively low zinc content is particularly advantageous for the use of the cast alloy in electrical components. For example, this method can be used to reduce the electrical and / or thermal conductivity of the alloy.

[0018] It can also prove advantageous if the casting alloy contains 12.0–23.5 wt.%, in particular 12.5–19.0 ​​wt.%, and further, in particular 18.0–18.5 wt.% zinc. In this respect, the casting alloy can contain at least 12.0 wt.%, in particular at least 12.5 wt.%, and further, in particular at least 18.0 wt.% zinc, and preferably at most 23.5 wt.%, in particular at most 19.0 wt.%, and further, in particular at most 18.5 wt.% zinc. In particular, the casting alloy can then contain 1.4–2.9 wt.%, in particular 1.5–2.4 wt.%, and further, in particular 2.0–2.1 wt.% molybdenum and 0.9–2.2 wt.%, in particular 1.3–1.8 wt.%, and further, in particular 1.4–1.7 wt.% sulfur. A medium zinc content can be particularly suitable for applications where machining is required.

[0019] It can also prove advantageous if the casting alloy contains 19.0–36.0 wt.%, in particular 21.5–32.0 wt.%, further in particular 22.0–30.5 wt.%, further in particular 22.5–27.5 wt.% zinc. In this respect, the casting alloy can contain at least 19.0 wt.%, in particular at least 21.5 wt.%, in particular at least 22.0 wt.%, further in particular 22.5 wt.%, and preferably at most 36.0 wt.%, in particular at most 32.0 wt.%, further in particular at most 30.5 wt.%, further in particular at most 27.5 wt.% zinc. In particular, the casting alloy may then contain 2.0 - 4.1 wt.%, in particular 2.3 - 4.0 wt.%, further in particular 2.6 - 3.6 wt.%, further in particular 2.7 - 3.5 wt.%, further in particular 3.0 - 3.2 wt.% molybdenum, and 1.3 - 3.1 wt.%, in particular 1.5 - 2.9 wt.%, further in particular 1.7 - 2.7 wt.%, further in particular 2.0 - 2.6 wt.%, further in particular 2.2 - 2.3 wt.% sulfur.A comparatively high zinc content can be advantageous, for example, for applications in bearing technology and / or construction, as a higher zinc content leads to a higher hardness and strength of the cast alloy.

[0020] As part of a beneficial further development, the casting alloy can contain 1.0–4.0 wt.%, in particular 1.5–4.0 wt.%, of iron. The addition of iron can increase the hardness and strength of the alloy. However, an excessively high iron content can reduce corrosion resistance.

[0021] Furthermore, it can be advantageous if the casting alloy contains 3.0–5.0 wt% silicon. Silicon, in combination with zinc, can improve mechanical strength and increase chip brittleness during machining by forming silicides. However, an excessively high silicon content can lead to undesirable oxide layers due to silicon's high affinity for oxygen.

[0022] Furthermore, it can prove advantageous if the casting alloy contains 1.0–7.0 wt.%, particularly 4.0–6.0 wt.%, of aluminum. Aluminum can contribute to the deoxidation of the melt. However, excessive aluminum content can lead to degeneration of the sulfur phase, which is why the aluminum content must be limited.

[0023] Furthermore, it can prove advantageous if the casting alloy contains 0.01–0.8 wt% phosphorus. Phosphorus can also contribute to the deoxidation of the melt. However, in combination with molybdenum disulfide, excessively high proportions can lead to degeneration of the sulfur phase and the formation of phosphorus-rich intermetallic phases, which, due to their hardness, can impair formability and increase brittleness. Therefore, the phosphorus content should be limited.

[0024] Furthermore, it is advantageous if the proportion of unavoidable impurities is less than 0.15 wt.%, in particular less than 0.1 wt.%, and more specifically less than 0.05 wt.%, and preferably totals no more than 0.8 wt.%, and in particular no more than 0.5 wt.%. The impurities may optionally include: up to 0.05 wt.% manganese, up to 0.1 wt.% lead.

[0025] The invention also relates to a casting, in particular a continuous casting, especially in continuous or tube form, made from one of the casting alloys described above. The casting is produced in particular by casting, especially continuous casting, a casting alloy described above to form a casting blank and optionally by machining the casting blank.

[0026] The casting consists in particular of 1.5 - 38.5 wt.%, in particular 7.0 - 38.5 wt.%, zinc; 0.6 - 4.2 wt.% molybdenum; 0.4 - 3.1 wt.% sulfur, optionally up to 4.5 wt.%, in particular up to 4.0 wt.%, iron; optionally up to 5.5 wt.%, in particular up to 5.0 wt.%, silicon; optionally up to 7.5 wt.%, in particular up to 7.0 wt.%, aluminum; optionally up to 0.8 wt.% phosphorus, balance copper and unavoidable impurities. wherein, based on weight percent, the ratio of sulfur to molybdenum in the alloy is greater than 0.6, in particular greater than 0.65, and further in particular at least 0.66, and wherein the total fraction of molybdenum and sulfur (i.e. the sum of the mass fraction (in wt.%) of molybdenum in the alloy and the mass fraction (in wt.%) of sulfur in the alloy) is more than 0.15 times the zinc fraction (i.e. the mass fraction (in wt.%) of zinc in the alloy).

[0027] In the cast alloy, particularly in the casting, a portion of the sulfur and molybdenum is present as molybdenum-sulfur phases. These molybdenum-sulfur phases have, in particular, the composition MoS₂-x, where 0 ≤ x < 1.1.

[0028] In particular, in the cast alloy, especially the casting, some of the sulfur and molybdenum is present as molybdenum disulfide (MoS₂), especially in the form of, preferably spherical, MoS₂ precipitates. Preferably, the molybdenum sulfide is finely dispersed within the microstructure.

[0029] Preferably, the molybdenum-sulfur phases constitute more than 1.0%, preferably more than 1.2%, and more preferably more than 1.4% of the total area considered when viewed in a polished section.

[0030] The surface area fraction of the molybdenum-sulfur phases can be determined, in particular, by preparing at least one metallographic section of the cast alloy, especially the casting, and examining a total area of ​​1.4 mm² at at least five positions on the section using a light microscope (e.g., at 200x to 400x magnification) and determining the surface area fraction of the molybdenum-sulfur phases. This determination of the surface area fraction of the molybdenum-sulfur phases can be performed using known measurement software.

[0031] Preferably, at least a subset of the molybdenum-sulfur phases, when viewed in a metallographic section, exhibit a surface area of ​​more than 30 µm². The surface area can be determined, for example, by light microscopy of a metallographic section of the cast alloy, particularly the casting itself. Molybdenum-sulfur phases of this size have proven to be particularly effective for lubrication. In such a configuration, it can be advantageous if, when viewed in a metallographic section, the surface area of ​​these molybdenum-sulfur phases exceeds 1.0%, preferably 1.2%, of the total surface area.

[0032] In particular, in the cast alloy, especially in the casting, some of the sulfur and zinc is present as zinc sulfide (ZnS).

[0033] Preferably, the cast alloy, and in particular the casting, has a base matrix consisting primarily of copper and zinc, in which ZnS-rich phases, particularly in the form of ZnS precipitates, are present, to which a molybdenum-sulfur phase, preferably a MoS₂-rich phase, particularly in the form of MoS₂ precipitates, is attached. In particular, the zinc sulfide is at least partially enclosed by a molybdenum-sulfur phase, particularly MoS₂, preferably spherically or at least with a rounded outer contour.

[0034] The invention also relates to a method for producing a casting alloy described above. The method comprises the following steps: Providing, in particular layers, of the alloying elements in a melting furnace, in particular an induction melting furnace, wherein the alloying elements are added at room temperature (the furnace itself, however, may have a higher temperature); generating a melt from the alloying elements in the melting furnace to form the alloy, in particular at temperatures between 1080°C and 1250°C.

[0035] It was discovered according to the invention that a homogeneous melt can be produced by providing, and in particular layering, the alloying elements at room temperature (i.e., the alloying elements are not preheated or added in a molten state). After the melt has been produced, it can be cast and then cooled.

[0036] The alloying elements can be provided in pure form or as an alloy or compound. In particular, sulfur can be added partially in the form of molybdenum disulfide (MoS₂), which improves the solubility of sulfur and molybdenum in the melt. The molybdenum disulfide is especially dissolved in the melt.

[0037] Furthermore, it has proven advantageous to cover the alloy components with a covering agent, particularly before and during the melting process, to protect the melt from environmental influences, especially oxidation. The covering agent can be, in particular, charcoal.

[0038] Furthermore, it can prove advantageous – as an alternative or in addition to covering the melt with the covering agent – ​​if the melt is produced under a protective gas atmosphere or under negative pressure.

[0039] The invention also relates to a method for producing a casting from a casting alloy as described above. The method comprises the following steps: The process involves generating a melt from the alloy components in a melting furnace, particularly an induction melting furnace, further specifically as described above; casting the melt; cooling (and thus solidifying) the melt, particularly to obtain a casting blank. The casting blank can form the final casting. The casting blank can also be further processed to obtain the final casting. Therefore, the process can optionally include processing the casting blank, in particular forming, heat treatment, and / or machining the casting blank.

[0040] The casting of the molten metal can be carried out in various ways. For example, casting the molten metal can involve one of the following processes: casting into a lost or permanent mold, sand casting, die casting, centrifugal casting, continuous casting, die casting, investment casting, or composite casting by centrifugal injection or injection molding. Continuous casting of the molten metal has proven to be particularly advantageous. Therefore, the casting alloy described above is also, in particular, a continuously cast alloy.

[0041] In particular, the alloy or casting blank exhibits a globular or dendritic microstructure after casting. The microstructure can be modified for specific applications through subsequent forming and / or heat treatments (e.g., rolling and recrystallization).

[0042] The invention also relates to the use of a casting alloy described above for the manufacture of jewelry, metal goods, semiconductor substrates, building facades, deep-drawn parts, stamped and bent parts, connectors, bearings, eyeglasses, precision engineering components, keys, locks, musical instruments, pumps and / or fittings. In this respect, the casting can be one of these components.

[0043] The following table summarizes advantageous compositions of the proposed casting alloy (values ​​in wt.%). Nr. Zn Mo S Fe And Al Total impurities change I 7,5-8,5 0,7-1,8 0,5-1,6 < 0,8 With yl 19,5-22,3 2,0-2,7 1,3-2,0 < 0,8 With III 12,5-16,5 1,5-2,2 1,0-1,7 < 0,8 With N 22,0-35,5 3,2-3,9 2,1-2,8 1,5-4,0 3,0-7,0 < 0,8 With V 27,0-30,0 2,7-3,4 1,8-2,5 < 0,8 With VI 23,0-27,0 2,4-3,1 1,6-2,3 1,0-4,0 4,0-6,0 < 0,8 With VII 18,0-23,0 2,1-2,8 1,4-2,1 1,0-3,5 < 0,8 With quick 13,0-18,0 1,6-2,3 1,0-1,7 3,0-5,0 < 0,8 With IX 8,0-13,0 1,1-1,8 0,7-1,4 < 0,8 With X 2,0-8,0 0,6-1,4 0,4-1,1 < 0,8 With XI 28,5-31,5 2,8-3,5 1,9-2,6 < 0,8 With XII 34,5-38,0 3,4-4,1 2,3-3,0 < 0,8 With

[0044] The Figure 1This simplified schematic representation shows typical microstructures of a cast alloy. The microstructures were extracted from a micrograph taken under a light microscope.

[0045] As in Figure 1 In schematic representation, the cast alloy has a base matrix 10 consisting primarily of copper and zinc. ZnS-rich phases 12, particularly in the form of ZnS precipitates, are present in the base matrix 10 (in Figure 1(shown hatched). A MoS₂-rich phase 14 is deposited on the ZnS-rich phases 12, preferably completely enclosing the ZnS phase 12. As mentioned above, this reduces the damaging effects of the ZnS. Furthermore, pure MoS₂-rich phases 14, preferably spherical or nodular, can be present in the base matrix 10. These MoS₂-rich phases 14 can serve as a dry lubricant and thus improve the tribological properties of the casting alloy or a casting produced therefrom.

Claims

1. Copper-zinc-molybdenum casting alloy, consisting of: 1.5 - 38.5 wt.%, in particular 7.0 - 38.5 wt.%, zinc; 0.6 - 4.2 wt.% molybdenum; 0.4 - 3.1 wt.% sulfur; optionally: up to 4.5 wt.%, in particular up to 4.0 wt.%, iron; up to 5.5 wt.%, in particular up to 5.0 wt.%, silicon; up to 7.5 wt.%, in particular up to 7.0 wt.%, aluminum; up to 0.8 wt.% phosphorus; balance copper and unavoidable impurities, wherein, based on wt. percent, the ratio of sulfur to molybdenum in the alloy is greater than 0.6, and wherein the total proportion of molybdenum and sulfur is more than 0.15 times the proportion of zinc.

2. Copper-zinc-molybdenum casting alloy according to claim 1, wherein the ratio of sulfur to molybdenum in the alloy is at most 2.5, in particular at most 2.0, further in particular at most 1.5, further in particular at most 1.0, further in particular at most 0.

8.

3. Copper-zinc-molybdenum casting alloy according to claim 1 or 2, wherein the alloy contains 1.0 - 4.0 wt.%, 1.4 - 3.6 wt.%, further in particular 1.5 - 3.2 wt.%, further in particular 1.6 - 2.9 wt.%, further in particular 1.7 - 2.4 wt.%, further in particular 1.8 - 1.9 wt.% molybdenum.

4. Copper-zinc-molybdenum casting alloy according to any of the preceding claims, wherein the alloy contains 0.4 - 2.9 wt.%, in particular 0.5 - 2.7 wt.%, further in particular 0.6 - 2.6 wt.%, further in particular 0.9 - 2.4 wt.%, 1.2 - 2.2 wt.%, further in particular 1.3 - 1.8 wt.%, further in particular 1.4 - 1.6 wt.% sulfur.

5. Copper-zinc-molybdenum casting alloy according to claim 1 or 2, wherein the alloy contains 2.0 - 13.5 wt.%, in particular 7.0-9.0 wt.%, and further in particular 7.5-8.5 wt.%, zinc.

6. Copper-zinc-molybdenum casting alloy according to the preceding claim, wherein the alloy contains 0.6 - 1.9 wt.%, in particular 1.0 - 1.8 wt.%, further in particular 1.1 - 1.4 wt.% molybdenum, and 0.4 - 1.7 wt.%, in particular 0.5 - 1.5 wt.%, further in particular 0.7 - 1.2 wt.% sulfur.

7. Copper-zinc-molybdenum casting alloy according to claim 1 or 2, wherein the alloy contains 12.0 - 23.5 wt.%, in particular 12.5 - 19.0 wt.%, and further in particular 18.0 - 18.5 wt.% zinc.

8. Copper-zinc-molybdenum casting alloy according to the preceding claim, wherein the alloy contains 1.4 - 2.9 wt.%, in particular 1.5 - 2.4 wt.%, further in particular 2.0 - 2.1 wt.% molybdenum and 0.9 - 2.2 wt.%, in particular 1.3 - 1.8 wt.%, further in particular 1.4 - 1.7 wt.% sulfur.

9. Copper-zinc-molybdenum casting alloy according to claim 1 or 2, wherein the alloy contains 19.0 - 36.0 wt.%, in particular 21.5 - 32.0 wt.%, further in particular 22.0 - 30.5 wt.%, further in particular 22.5 - 27.5 wt.% zinc.

10. Copper-zinc-molybdenum casting alloy according to the preceding claim, wherein the alloy contains 2.0 - 4.1 wt.%, in particular 2.3 - 4.0 wt.%, further in particular 2.6 - 3.6 wt.%, further in particular 2.7 - 3.5 wt.%, further in particular 3.0 - 3.2 wt.% molybdenum, and 1.3 - 3.1 wt.%, in particular 1.5 - 2.9 wt.%, further in particular 1.7 - 2.7 wt.%, further in particular 2.0 - 2.6 wt.%, further in particular 2.2 - 2.3 wt.% sulfur.

11. Casting, in particular continuous casting, especially in continuous or tube form, produced by casting a copper-zinc-molybdenum casting alloy according to one of the preceding claims.

12. Casting according to the preceding claim, wherein a portion of the sulfur is in the form of molybdenum-sulfur phases of the composition MoS 2-x with 0 ≤ x < 1.1, especially as MoS2.

13. Casting according to the preceding claim, wherein, when viewed in the polished section, the surface area fraction of the molybdenum-sulfur phases is more than 1.0%, preferably more than 1.2%, further preferably more than 1.4%.

14. Casting according to claim 12 or 13, wherein at least a subset of the molybdenum-sulfur phases has a surface area of ​​at least 30 µm² when viewed in a polished section. 2 exhibit.

15. Casting according to one of claims 12 to 14, wherein part of the sulfur is present as zinc sulfide, wherein a molybdenum-sulfur phase, in particular a MoS2-rich phase, is attached to the zinc sulfide.

16. Method for producing a copper-molybdenum-sulfur alloy according to any one of claims 1 to 10, comprising: - layering the alloying elements in a melting furnace, in particular an induction melting furnace, wherein the alloying elements are added at room temperature; - generating a melt from the alloying elements in the melting furnace.

Images