Copper-zinc-nickel-manganese alloy

Abstract

A copper alloy having the following composition (in % by weight) Zn: 17 to 20.5%, Ni: 17 to 23%, Mn: 8 to 11.5%, optionally up to 4% Cr, optionally up to 5.5% Fe, optionally up to 0.5% Ti, optionally up to 0.15% B, optionally up to 0.1% Ca, optionally up to 1.0% Pb, balance copper and unavoidable impurities, wherein the proportion of copper is at least 45% by weight. Further, the ratio of the proportion of Ni to the proportion of Mn is at least 1.7 and the alloy has a microstructure which has inclusions of MnNi and MnNh precipitates.

Claims

1. A wrought material of a copper alloy having a composition (in % by weight) consisting of: Zn: from 17 to 20.5%, Ni: from 17 to 23%, Mn: from 8 to 11.5%, up to 4% of Cr, up to 5.5% of Fe, up to 0.5% of Ti, up to 0.15% of B, up to 0.1% of Ca, up to 1.0% of Pb, the balance being copper and unavoidable impurities, wherein the proportion of copper is at least 45% by weight, the ratio of the proportion of Ni to the proportion of Mn is at least 1.7 and the alloy has a microstructure in which precipitates of the type MnNi and MnNi.sub.2 are embedded, wherein the wrought material has a tensile strength of at least 1100 MPa and is obtained by hot forming in a temperature range between 650° C. and 850° C., cold forming, and heat treatment of 2 to 30 hours in a temperature range between 310° C. and 370° C.

2. The wrought material as claimed in claim 1, wherein the ratio of the proportion of Ni to the proportion of Mn is not more than 2.3.

3. The wrought material as claimed in claim 1, wherein the ratio of the proportion of Ni to the proportion of Mn is at least 1.8.

4. The wrought material as claimed in claim 1, wherein the proportion of Zn is not more than 19.5% by weight.

5. The wrought material as claimed in claim 1, wherein the alloy has a microstructure comprising an α-phase matrix having a proportion of β-phase embedded therein of not more than 2% by volume and the precipitates of the type MnNi and MnNi.sub.2 are embedded in the α-phase matrix.

6. The wrought material as claimed in claim 5, wherein the α-phase matrix of the microstructure is free of β-phase.

7. The wrought material as claimed in claim 3, wherein the ratio of the proportion of Ni to the proportion of Mn is at least 1.9.

8. A wrought material made of a copper alloy having a composition (in % by weight) consisting of: Zn: from 17 to 20.5%, Ni: from 17 to 23%, Mn: from 8 to 11.5%, up to 4% of Cr, up to 5.5% of Fe, up to 0.5% of Ti, up to 0.15% of B, up to 0.1% of Ca, up to 1.0% of Pb, the balance being copper and unavoidable impurities, wherein the proportion of copper is at least 45% by weight, the ratio of the proportion of Ni to the proportion of Mn is at least 1.7 and the wrought material has a microstructure in which precipitates of the type MnNi and MnNi.sub.2 are embedded, wherein the wrought material has an elongation of break of at least 30% and is obtained by hot forming in a temperature range between 650° C. and 850° C., cold forming, and a heat treatment at a temperature above 450° C. and a duration of heat treatment below one hour.

9. A wrought material made of a copper alloy having a composition (in % by weight) consisting of: Zn: from 17 to 20.5%, Ni: from 17 to 23%, Mn: from 8 to 11.5%, up to 4% of Cr, up to 5.5% of Fe, up to 0.5% of Ti, up to 0.15% of B, up to 0.1% of Ca, up to 1.0% of Pb, the balance being copper and unavoidable impurities, wherein the proportion of copper is at least 45% by weight, the ratio of the proportion of Ni to the proportion of Mn is at least 1.7 and the wrought material has a microstructure in which precipitates of the type MnNi and MnNi.sub.2 are embedded, wherein the wrought material has a tensile strength of at least 850 MPa and an elongation of break of at least 3% and is obtained by casting, cold forming of the cast state without any hot forming, and a heat treatment of 10 minutes to 30 hours in a temperature range between 310° C. and 500° C., the cold forming having a total degree of deforming of at least 80%.

Description

(1) The invention will be illustrated with the aid of working examples. The figures show:

(2) FIG. 1 a graph in which the hardness of the alloy is plotted against the proportion of manganese.

(3) FIG. 2 a graph in which tensile strength, yield point and elongation at break of the alloy before precipitation heat treatment are plotted against the proportion of manganese.

(4) FIG. 3 a graph in which the tensile strength and yield point of the alloy after precipitation heat treatment are plotted against the proportion of manganese.

(5) Samples having the composition shown in Table 1 were produced.

(6) TABLE-US-00001 TABLE 1 Composition of the samples in % by weight Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Cu 55% 52.5%.sup.  50% 47.5% 45% Zn 20% 20% 20% .sup. 20% 20% Ni 20% 20% 20% .sup. 20% 20% Mn  5% 7.5%  10% 12.5% 15% Crack no no no yes yes formation

(7) In the samples, the proportions of zinc and nickel were kept constant at 20% by weight each. The proportion of manganese was varied from 5% by weight to 15% by weight. Correspondingly, the proportion of copper decreased from 55% by weight to 45% by weight. The unavoidable impurities were less than 0.1% by weight.

(8) The samples were melted and cast. After solidification, the cast blocks were hot rolled at 775° C. In the last row of the table, crack formation during hot rolling is documented. After hot rolling, the samples were cold rolled with a degree of deformation of 90%. In this state, hardness, tensile strength, yield point and elongation at break were measured on the samples.

(9) After cold rolling, the samples were heat treated at 320° C. for 12 hours. After the heat treatment, hardness, tensile strength, yield point and elongation at break were likewise measured.

(10) FIG. 1 shows a graph in which the hardness of the alloy is plotted against the proportion of manganese. The bottom row of measurement points represents the measured values for the state immediately after cold rolling, i.e. without heat treatment, while the upper points in the graph represent the measured values after the heat treatment. Without heat treatment, the alloy displays a steady increase in the hardness from 270 to 290 HV10 with increasing proportion of manganese. The hardness of the alloy increases significantly as a result of heat treatment. The increase at 5 and 7.5% by weight is about 50 HV10, while the increase in the hardness is more than 80 HV10 at a proportion of manganese of at least 10% by weight. The increase in the hardness resulting from the precipitation heat treatment is significantly more pronounced at a proportion of manganese above 7.5% by weight than at smaller proportions of manganese. About 9% by weight of manganese is necessary to increase the hardness of the material to at least 350 HV10. A hardness of 350 HV10 and more is advantageous for, for example, sliding bearings. The alloy is thus able to replace Cu—Be alloys as sliding bearing material.

(11) FIG. 2 shows a graph in which the tensile strength, the yield point and the elongation at break are plotted against the proportion of manganese in the alloy before heat treatment. The values for the tensile strength are depicted as solid circles, while those for yield point are represented by open squares. Tensile strength and yield point relate to the left-hand axis of the graph. The values for elongation at break are represented by the open triangles and relate to the right-hand axis of the graph. A moderate increase in the tensile strength and the yield point is found at from 5 to 10% by weight of manganese. From 10 to 12.5% by weight of manganese, the tensile strength and the yield point decrease a little. At 15% by weight of manganese, values of tensile strength and yield point which are somewhat above the level of the values at 10% by weight are measured. The elongation at break decreases slightly in the range from 5 to 10% by weight of manganese, but drops significantly from 3% to about 1% at higher proportions of manganese.

(12) FIG. 3 shows a graph in which the tensile strength and the yield point are plotted against the proportion of manganese in the alloy after heat treatment. The values for tensile strength are represented by solid circles, while the values for the yield point are represented by open squares. A significant increase in the tensile strength and the yield point is found from 5 to 10% by weight of manganese. In particular, the yield point increases from less than 900 MPa to 1200 MPa in this range. From 10 to 12.5% by weight of manganese, the tensile strength and the yield point decrease slightly. At 15% by weight of manganese, values which correspond to the level of the values at 10% by weight are measured for the tensile strength and the yield point.

(13) A comparison of the values in FIG. 2 and FIG. 3 shows that the effect of strengthening by heat treatment is particularly large for a proportion of manganese above 7.5% by weight. At a proportion of manganese of 10% by weight, the tensile strength and the yield point were each increased by virtually 300 MPa by the heat treatment, while at 5% by weight of manganese the tensile strength was increased by only about 130 MPa by the heat treatment and the yield point was barely changed.

(14) The results of the studies show that very favorable conditions in the alloy are present at a proportion of manganese of about 10% by weight. Firstly, tensile strength and yield point display a maximum, and secondly the alloy does not have a tendency to form cracks in this region.