Copper-zinc alloy, band material composed thereof, process for producing a semifinished part composed of a copper-zinc alloy and sliding element composed of a copper-zinc alloy

Abstract

A copper-zinc alloy having the following composition (in % by weight): from 67.0 to 69.0% of Cu, from 0.4 to 0.6% of Si, from 1.2 to 1.6% of Mn, from 0.03 to 0.06% of P, optionally up to a maximum of 0.5% of Al, optionally up to a maximum of 0.15% of Ni, optionally up to a maximum of 0.1% of Fe, optionally up to a maximum of 0.1% of Pb, optionally up to a maximum of 0.08% of Sn, optionally up to a maximum of 0.1% of S,
balance Zn and unavoidable impurities. The alloy has a microstructure which consists of an -phase matrix in which inclusions of manganese silicides having a globular shape are present in a proportion of at least 2% by volume and not more than 5% by volume.

Claims

1. A copper-zinc alloy consisting of, in % by weight: from 67.5 to 68.3% of Cu, from 0.43 to 0.46% of Si, from 1.32 to 1.35% of Mn, from 0.035 to 0.043% of P, optionally up to a maximum of 0.5% of Al, optionally up to a maximum of 0.15% of Ni, optionally up to a maximum of 0.1% of Fe, optionally up to a maximum of 0.1% of Pb, optionally up to a maximum of 0.08% of Sn, optionally up to a maximum of 0.1% of S, balance Zn and unavoidable impurities, characterized in that the alloy has a microstructure which consists of an -phase matrix in which inclusions of manganese silicides having a globular shape are present in a proportion of at least 2% by volume and not more than 5% by volume.

2. A copper-zinc alloy according to claim 1, characterized in that the ratio of Cu content of the alloy to the Zn equivalent of the alloy is at least 2.1 and not more than 2.4, where the Zn equivalent of the alloy is calculated as follows from the proportions of the respective alloying elements, in % by weight:
Zn equivalent=proportion of Zn+0.9proportion of Fe1.3proportion of Ni+6proportion of Al+2proportion of Sn.

3. A copper-zinc alloy according to claim 1, characterized in that the sum of iron content and nickel content is not more than 0.22% by weight.

4. A copper-zinc alloy according to claim 1, characterized in that manganese silicides having a stem-like shape are additionally present in the matrix, with the longitudinal extension of these manganese silicides being not more than 50 m and the number of the manganese silicides having a stem-like shape being not more than 2% of the number of the manganese silicides having a globular shape.

5. A band material composed of a copper-zinc alloy according to claim 1.

6. A process for producing a semifinished part composed of a copper-zinc alloy according to claim 1, where the process comprises the following steps: a) melting of the alloy, b) casting of a cast body, c) cold forming, d) heat treatment, characterized in that the process comprises only cold forming steps as forming steps.

7. A process according to claim 6 for producing a band-like semifinished part, characterized in that a band having a thickness of not more than 20 mm is cast in process step b).

8. A process according to claim 7, characterized in that the casting of the band in process step b) is carried out continuously.

9. A sliding element, characterized in that it consists entirely or at least partly of a copper-zinc alloy according to claim 1.

10. A sliding element, characterized in that it consists entirely or at least partly of a band material according to claim 5.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is illustrated with the aid of the following examples and the FIGURE. The FIGURE shows:

(2) FIG. 1 a polished section of a material composed of an alloy according to the invention.

DETAILED DESCRIPTION

(3) For experiments, two alloys according to the invention and four comparative alloys were produced. The composition of the alloys in % by weight is shown in table 1. The respective Zn equivalent (in % by weight) is given in the penultimate column of the table. In the last column, the value for the ratio of Cu content of the alloy to the Zn equivalent of the alloy is indicated. The two test alloys as per rows 1 and 2 of table 1 and also the comparative alloy 4 have a pure -phase matrix, while the three comparative alloys 1, 2 and 3 as per rows 3 to 5 have a microstructure comprising - and -phase. The reason for the latter is the relatively high Zn equivalent of these alloys.

(4) TABLE-US-00001 TABLE 1 Composition of the test and comparative alloys in % by weight Zn Cu/Zn Cu Zn Mn Fe Ni Si Al P Pb Sn Others eq. eq. Test 1 67.5 30.2 1.32 0.08 0.14 0.43 0.25 0.035 0.05 0.002 0.02 31.572 2.14 Test 2 68.3 29.3 1.35 0.05 0.10 0.46 0.33 0.043 0.03 0.002 0.02 31.214 2.19 Comp. 1 63.8 31.4 1.90 0.33 0.58 0.93 0.91 0.003 0.07 0.008 0.04 36.40 1.75 Comp. 2 65.0 30.2 1.94 0.30 0.76 0.84 0.80 0.004 0.09 0.032 0.01 34.31 1.89 Comp. 3 64.5 32.7 0.89 0.26 0.40 0.63 0.49 0.003 0.06 0.007 0.04 35.35 1.82 Comp. 4 69.7 27.9 0.88 0.23 0.38 0.42 0.43 0.036 0.04 0.008 0.02 30.19 2.31

(5) The alloys were each melted in an amount of about 3000 kg and continuously cast as a band having a thickness of 13 mm. The cast band was rapidly cooled, heat treated, milled and rolled to a band thickness of 2.5 mm in four cold forming steps with intermediate heat treatment in each case. Finally, it was subjected to a heat treatment to relieve stresses. The two test alloys as per rows 1 and 2 of table 1 and the comparative alloy 4 could be rolled without difficulties to the final dimensions, while the comparative alloys 1, 2 and 3 could be processed only unsatisfactorily: comparative alloys 1 and 2 displayed defects even during casting. The reduction in the amount of silicide-forming elements in the case of comparative alloy 3 did lead to a stable casting process, but this alloy tended to suffer from crack formation and other problems during cold rolling. In this regard, an improvement could be achieved in the case of comparative alloy 4 by the proportion of copper being increased and the proportion of zinc being decreased compared to comparative alloy 3 and a matrix having a pure -microstructure thus being produced.

(6) The ductility of bearing materials both at ambient temperature and at elevated temperature is an important property in the case of bearings subjected to high stresses. The elongations at break at 20 C. and at 300 C. were therefore determined on specimens which had an alloy composition as per test 2. At a band thickness of 2.5 mm, an elongation at break of 28% could be achieved at 20 C. and of over 40% could be achieved at 300 C. In the case of a further specimen whose band thickness after five cold forming steps was 1.2 mm, the elongation at break was still above 20% at 20 C. and above 25% at 300 C. Comparative specimens produced from the alloy as per the row Comparison 3 did achieve elongation at break values at ambient temperature which are only slightly below those of the inventive alloy, but at 300 C. elongation at break values of only 12% at a band thickness of 1.2 mm and 6% at a band thickness of 2.5 mm could be achieved on the comparative specimens. A lower elongation at break value at 300 C. than at 20 C. was also determined on comparative specimens produced from the alloy as per the row Comparison 4. This comparison shows the particular advantages of the inventive alloy for applications in bearings which are subjected to high stresses.

(7) Specimens composed of the alloys Test 2 and Comparison 4 were subjected to wear tests. Here, the specimen composed of the inventive alloy Test 2 displayed significantly better properties than the specimen composed of the alloy Comparison 4. In the wear test, the removal of material from the specimen Test 2 was about 30% lower than in the case of the specimen Comparison 4. This comparison shows that the selection of the silicide-forming elements, namely Mn, Si, Fe and Ni, has to be made within a very narrow window in order to produce a material having advantageous properties as sliding bearing.

(8) FIG. 1 shows a polished section of an alloy according to the invention as per Test 2. It can be seen that the microstructure of the material 1 consists only of one phase, namely the -phase. Finely dispersed manganese silicides 2 having a globular shape are embedded in this matrix. The individual globular manganese silicides 2 are very small. The distribution of the globular manganese silicides 2 is not completely homogeneous. There are regions 21 in which the density of the globular manganese silicides 2 is increased compared to the average density. There are likewise regions 22 in which the density of the globular manganese silicides 2 is decreased compared to the average density. These regions 22 appear as lighter-colored spots in the polished section. This variation in the density of the globular manganese silicides 2 gives a picture in which accumulations of globular manganese silicides 2 appear like clouds.

(9) Apart from the globular manganese silicides 2, manganese silicides 3 having a stem-like shape are visible. As can easily be seen, a plurality of individual silicide particles having a small distance between them are arranged along a line in the case of the stem-like manganese silicides 3. The individual silicide particles of such an arrangement are larger than the globular manganese silicides 2. The size of the individual silicide particles belonging to a stem-like manganese silicide 3 is typically in the range from 1 m to 10 m. The longitudinal extension of the stem-like manganese silicides 3 is from about 20 to 30 m, at most 40 m. In the immediate vicinity of a stem-like manganese silicide 3, there are significantly fewer globular manganese silicides 2 to be found than in the other regions. This depletion can be explained by the primary precipitates growing together locally as a result of diffusion to form larger precipitates on solidification of the alloy. These larger precipitates are broken up in the subsequent cold forming steps and the fragments are aligned along the forming direction. This gives the specific appearance of the stem-like manganese silicides 3.

LIST OF REFERENCE NUMERALS

(10) 1 material 2 manganese silicide having a globular shape 21 region having a high density of manganese silicides having a globular shape 22 region having a low density of manganese silicides having a globular shape 3 manganese silicide having a stem-like shape