MANGANESE AND ALUMINUM-CONTAINING COPPER-ZINC ALLOY

Description

[0001] The invention relates to a copper-zinc alloy containing manganese and aluminum.

[0002] Cu-Zn-Al and Cu-Al-Mn alloys are known from the state of the art, e.g., as shape memory alloys or Heusler alloys. Cu-Al-Mn alloys generally exhibit higher strengths than Cu-Zn-Al alloys. Cu-Al-Mn alloys with high manganese contents but low Al contents are readily hot-formable, but their tensile and compressive strengths are limited to 800 to 1000 MPa. CuMn31Al6, for example, has a tensile and compressive strength of 800 MPa. While high Al contents in Cu-Al-Mn alloys lead to high compressive strengths of over 1500 MPa, they also impair hot-formability, making these alloys difficult to hot-form.

[0003] Quaternary Cu-Zn-Mn-Al alloys are less well known. With Mn and Al contents of less than 10 wt.% each, quaternary Cu-Zn-Mn-Al alloys are limited in strength, hardness, and wear resistance. CuZn23Mn6Al6 has a hardness of 262 HV0.1 in the as-cast condition. CuZn23Mn10Al8 achieves a tensile and compressive strength of approximately 660 MPa and a hardness of 466 HV0.1 in the hot-rolled and age-hardened condition.

[0004] US Pat. No. 4,166,739 describes an alloy containing 70 to 82 wt.% copper, 6 to 10 wt.% aluminum, 0.1 to 24 wt.% zinc, and 0.1 to 12 wt.% manganese. It is a shape memory alloy. The alloy is very ductile.

[0005] JP H03 264630 A discloses a Cu-Al-Mn-Zn alloy with the composition Zn: 5.7 wt.%, Mn: 26.5 wt.%, Al: 10.7 wt.%, the remainder Cu and unavoidable impurities. To avoid impairing the hot formability of the alloy, the zinc content should not exceed 20 wt.%.

[0006] The invention is based on the object of providing a cost-effective, lightweight, and highly wear-resistant alloy with high hardness. Furthermore, the alloy should be hot-formable.

[0007] The invention is defined by the features of claim 1. The further dependent claims relate to advantageous embodiments and developments of the invention.

[0008] The invention includes a copper-zinc alloy having the following composition in wt.%: Zn: 25.0 to 32.0% Mn: 20.0 to 27.0% Al: 11.0 to 14.0% optional Fe: 0.05 to 5.0% optional Cr: 0.02 to 2.0% optional Ni: 0.02 to 2.0% optional Ti: 0.01 to 0.5% optional B: 0.002 to 0.15% optional C: 0.001 to 0.1% optional Ca: 0.01 to 0.1%

[0009] Rest Cu and unavoidable impurities.

[0010] To obtain a copper alloy with a hardness of 780 HV0.1 and a low density, the zinc content must be at least 25 wt.%, the manganese

[0011] The zinc content must be at least 20% by weight and the aluminum content at least 11% by weight. The density of the copper alloy is a maximum of 6500 kg / m 3< , typically 6250 kg / m 3< . In order for the alloy to be hot-formed by extrusion, the zinc content must not be greater than 32% by weight, the manganese content must not be greater than 27% by weight and the aluminum content must not be greater than 14% by weight. Hot-forming takes place at a temperature between 700 and 800 °C. In this temperature range, the alloy has a single-phase, body-centered cubic crystal structure. This crystal structure allows reliable hot forming at moderate forming speeds in this temperature range.

[0012] The alloy exhibits many special properties. It achieves a Vickers hardness of up to 790 HV0.1, which corresponds to over 63 HRC (Rockwell hardness). This high hardness of the material results in high wear resistance. The alloy is also characterized by a very high compressive strength of approximately 1600 MPa. This is roughly twice the compressive strength of cast iron. The 0.2% yield strength is 1500 MPa, and the tensile strength is approximately 250 MPa. The alloy has a Young's modulus of approximately 185 GPa, which is comparable to Cr-Ni stainless steel. Materials made from this alloy are ferromagnetic, allowing magnetic fixtures to be attached to components made from this material.

[0013] The optional alloying elements Fe, Cr, Ni, Ti, B, C and Ca cause grain refinement of the alloy.

[0014] In a preferred embodiment of the invention, the Zn content can be at least 28.0 wt.%. Increasing the zinc content at the expense of the copper content makes the alloy more cost-effective. Zinc, like manganese, reduces the density of the alloy, albeit to a lesser extent than aluminum. Zinc also improves hot formability.

[0015] Advantageously, the Mn content can be at least 23.0 wt.%. Manganese stabilizes the body-centered cubic crystal structure, improving hot formability. Manganese also reduces the alloy's price and density.

[0016] Furthermore, in a preferred embodiment of the invention, the Al content can be at least 12.0 wt.%. A high Al content leads to a reduction in the density of the alloy. Al also has a particularly strong strength-enhancing effect, which is considerably greater than the effect of manganese. CuZnMnAl alloys therefore have considerably higher strengths than, for example, CuZnMn alloys.

[0017] Advantageously, the Al content of the alloy can be selected so that it is no greater than one-quarter of the sum of the Zn and Mn contents. Alloys selected in this way are characterized by a particularly advantageous combination of strength, hardness, density, and hot formability.

[0018] In a particularly advantageous embodiment of the invention, the Zn content can be 30.0 to 31.5 wt.%, the Mn content 25.0 to 26.5 wt.%, and the Al content 12.0 to 13.5 wt.%. This alloy composition results in particularly favorable properties with regard to wear resistance, density, cost, and hot formability.

[0019] In an advantageous embodiment of the invention, the copper-zinc alloy in the as-cast state at room temperature can have a microstructure consisting of a Cu-Zn-rich γ-phase, a cubic solid solution phase in the structure of β-manganese, an Al-Cu-rich δ-phase, and an Al 8 Mn 5 phase. Such a microstructure transforms at temperatures between 700 and 800 °C into a single-phase microstructure consisting only of a body-centered cubic β-solid solution phase. This single-phase microstructure is sufficiently hot-formable, in particular extrudable, at low to moderate forming rates. The Cu-Zn-rich γ-phase can preferably have a volume fraction of approximately 40%.

[0020] The copper-zinc alloy can advantageously be used to produce semi-finished products, which are hot-formed, i.e., have undergone a hot-forming step. The hot-forming step can, in particular, be extrusion.

[0021] Alternatively, the copper-zinc alloy can also be used to coat a component. The coating can be applied, for example, by thermal spraying. Because the alloy is particularly characterized by its high wear resistance, tools and sliding elements are particularly suitable components.

[0022] The invention is explained in more detail using an embodiment.

[0023] A material from an alloy with the composition CuZn31Mn26Al13 was produced as follows: The alloy was melted in a Tammann furnace using the binary copper master alloys CuZn, CuMn, and CuAl. The melt was covered with graphite. The alloy was cast in the form of a billet.

[0024] In the same way, reference materials were produced in the as-cast state with a composition according to Table 1. Table 1 documents the hardness values ​​measured on the materials. Table 1: Material variants and hardness values material Hardness HV0.1 CuZn31Mn26Al13 790 CuZn23 Mn6Al6 (reference material) 262 CuZn23Mn10Al8 (reference material) 466 CuZn31 Mn10Al8 (reference material) 576 CuZn31Mn26Al8 (reference material) 665

[0025] Table 1 documents the exceptionally high hardness of CuZn31Mn26Al13. Compared to CuZn31Mn26Al8, it is 19% harder. At the same time, it is still hot-formable: The cast billet can be heated in a gas convection furnace and then extruded through a conical die at a moderate extrusion speed. The ratio between the cross-sectional area of ​​the billet and the cross-sectional area of ​​the extruded product is in the range of 5 to 10.

[0026] The high hardness of the CuZn31Mn26Al13 material results in outstanding wear properties. This was confirmed in a tribological endurance test conducted using a disc-on-plate tribometer. The CuZn31Mn26Al13 specimen showed virtually no wear-related weight loss, while significant weight loss was observed in comparison specimens made of typical sliding element materials.

Claims

1. Copper / zinc alloy having the following composition in % by weight: Zn: from 25.0 to 32.0% Mn: from 20.0 to 27.0% Al: from 11.0 to 14.0% optionally Fe: from 0.05 to 5.0% optionally Cr: from 0.02 to 2.0% optionally Ni: from 0.02 to 2.0% optionally Ti: from 0.01 to 0.5% optionally B: from 0.002 to 0.15% optionally C: from 0.001 to 0.1% optionally Ca: from 0.01 to 0.1%, balance Cu and inevitable impurities.

2. Copper / zinc alloy according to claim 1, wherein the Zn proportion is at least 28.0% by weight.

3. Copper / zinc alloy according to claim 1 or 2, wherein the Mn proportion is at least 23.0% by weight.

4. Copper / zinc alloy according to any one of the preceding claims, wherein the Al proportion is at least 12.0% by weight.

5. Copper / zinc alloy according to any one of the preceding claims, characterised in that the Al proportion is not greater than a quarter of the sum of the proportions of Zn and Mn.

6. Copper / zinc alloy according to any one of the preceding claims, characterised in that the Zn proportion is from 30.0 to 31.5%, the Mn proportion is from 25.0 to 26.5% by weight and the Al proportion is from 12.0 to 13.5% by weight.

7. Copper / zinc alloy according to any one of the preceding claims, characterised in that the alloy in the cast state at ambient temperature has a structure which comprises a Cu / Zn-rich γ phase, a cubic mixed crystal phase in the structure of the β manganese, an Al / Cu-rich δ phase and an AL8Mn5 phase.

8. Semi-finished product comprising a copper / zinc alloy according to any one of the preceding claims, characterised in that the semi-finished product is hot-formed, in particular extruded.

9. Component having a coating comprising a copper / zinc alloy according to any one of claims 1 to 7.