GB2049727A

GB2049727A - A Copper/Zinc Alloy and use Thereof

Info

Publication number: GB2049727A
Application number: GB7923649A
Authority: GB
Original assignee: Diehl GmbH and Co
Current assignee: Diehl Verwaltungs Stiftung
Priority date: 1979-05-15
Filing date: 1979-07-06
Publication date: 1980-12-31
Also published as: DE2919478C2; DE2919478A1

Abstract

In a copper/zinc alloy having a structure in which a constituent of cubic face centred alpha -mixed crystal is embedded into a base matrix of cubic body centred beta -mixed crystal, the alloy consists of 60 to 75 percent Cu, 6 to 8 percent Mn, 4 to 6 percent Al, 1 to 4 percent Si, 1 to 3 percent Fe, 0.5 to 1.5 percent Pb, up to 0.2 percent Ni, up to 0.2 percent Sn, remainder Zn, and has a structure in which 60 to 85 percent, alpha -mixed crystals are embedded in predominantly finely- dispersed distribution in the beta -phase. The alloy may be used for example, in synchronising rings.

Description

SPECIFICATION A Copper/Zinc Alloy and Use Thereof The invention relates to a copper/zinc alloy having a structure in which a constituent of cubic face centered a-mixed crystal is embedded into a base matrix of cubic body centered mixed crystal, and to use of such an alloy.

Copper/zinc alloys having such an mixed structure are already known in the prior art. Thus, already known from German Auslegeschrift No.

11 94 592 is a method of producing semifinished products or semi-manufactured products in which, starting from a special brass, there is produced as a result of a special heat treatment a material having a mixed structure in which 5 to 50 percent a-precipitation is present in the ss- phase. The semi-finished products and semimanufactured products produced therefrom are used for products in which good workability, uniform coefficient of friction and high resistance to wear are required, more especially for synchronising rings.

Furthermore, for the same purpose, it is already known from German Offenlegungsschrift No.

15 58 817 also to produce, in the case of other base alloys, such as for example copper/aluminium, a similar a/p-mixed structure in which similarly 5 to 50 percent a-proportion is present in the /3-mother phase. The alloys used in this respect contain, in addition to a Cu content of at least 50 percent, mandatory additions of Al, Ni and Mn and may furthermore contain Zn, Fe, Si, P, Pb and Sn. In this respect, as a result of a great range of variation of the additives, the possibilities of coordinating the mechanical properties of the material to one another and in this way of achieving for example over a wide strength range of unvarying or constant coefficient of friction, are improved.

However, it has become apparent that more especially the aluminium bronzes proposed in German Auslegeschrift No. 1 5 58 817, for example of the type CuAI 1 OFe or CuAI 1 ONi, nowadays may no longer in every instance satisfy the increased stresses which are made on synchronising rings as a result of higher engine performances as well as new construction principles in automobile construction. In appropriate tests-at least for the tested type of gearing-synchronising rings produced from these materials failed prematurely as a result of excessive wear at the friction thread.

In order, in view of such shortcomings, nevertheless to adapt to some extent the wear properties of materials for synchronising rings to the requirements, more and more frequent use is being made of special brasses which are provided with an additional coating, for example of molybdenum. However, this measure can, for reasons of cost alone, only bear the character of a makeshift solution.

A task of the invention is to provide a material the mechanical properties of which are, as compared with those of materials previously used to produce synchronising rings, improved to such an extent that they fully meet the increased demands, more especially with respect to wear resistance. In this respect, this material should be well workable and simple and inexpensive to produce.

According to the invention, there is provided a copper/zinc alloy having a structure in which a constituent of cubic face centered a-mixed crystal is embedded into a base matrix of cubic body centered mixed crystal, characterised in that the alloy consists of 60 to 75 percent Cu, 6 to 8 percent Mn, 4 to 6 percent Al, 1 to 4 percent Si, 1 to 3 percent Fe, 0.5 to 1.5 percent Pb, up to 0.2 percent Ni, up to 0.2 percent Sn, the remainder being Zn, and has a structure in which 60 to 85 percent a-mixed crystals are embedded in predominantly finely-dispersed distribution in the phase. Preferably, the alloy has a structure in which approximately 65 to 70 percent a-mixed crystals are embedded in predominantly finelydispersed distribution in the phase.

Synchronising rings produced from this alloy not only have a considerably improved resistance to wear, but at the same time they have a considerably enhanced friction value.

Furthermore, semi-finished products produced from an alloy in accordance with the invention have good workability, in which respect, by virtue of the relatively high content of aluminium and although as compared with the previously customary special brasses a hardness rise at room temperature can be registered, they can be coldformed astonishingly well.

The pressure of the proportions of 1 to 3 percent Fe, 6 to 8 percent Mn and 1 to 4 percent Si which are mandatorily provided for in the copper/zinc alloy in accordance with the invention leads to the formation of relatively hard intermetallic compounds, the existence of which is a pre-requisite for an improved resistance to wear.

As a result of this fine distribution of the amixed crystals there emerges a uniform contact reflection (Tragbild) of synchronising rings produced from an alloy in accordance with the invention: at the same time the a-content ensures the ductiiity of the material.

The proportion of amixed crystal (60 to 85 percent), which is high as compared with normal synchronising ring alloys of special brass, has a favourable effect with regard to a high coefficient of friction.

In a preferred composition the alloy has a copper content which is above 70, at a maximum at about 73, percent Cu. This alloy range is advantageous with respect to achieving the structure composition provided for in accordance with the invention. To adjust the proportion of aphase provided for in accordance with the invention it does not require in this range possible additional annealing, for instance in the form of a precipitation after a shaping process.

It proves to be particularly advantageous with regard to achieving the highest possible resistance to wear if the copper/zinc alloy in accordance with the invention has less than 0.05 percent Ni and less than 0.05 percent Sn.

Preferabiy, a copper/zinc alloy in accordance with the invention has a composition with a copper content of 70.5 percent, an aluminium content of 5.15 percent and a zinc content of about 14 percent. It is a matter of a material which lies, in alloy technology respects, between the special brasses and the aluminium bronzes and which in this respect combines the proven properties of the special brass with respect to friction behaviour and hot- and cold-workability, with those of the aluminium bronzes which are more resistant to wear.

An alloy of a similar composition, but without a mandatory proportion of iron, can indeed already be derived from the alloying limits indicated in German Offenlegungsschrift No. 21 45 710, but in the said specification a use of the material is intended for parts which are exposed to considerable frictional stresses at high temperatures, for example for valve seats for internal-combustion engines. Such materials must indeed also possess a good resistance to wear, more especially at high temperatures, as well as the most constant possible coefficient of friction, but what is important in this respect is that this coefficient of friction is as low as possible in order to keep the friction stress low.

It is ali the more surprising that an alloy which, from its analytical composition, at least lies partially in the region indicated in German Offenlegungsschrift No. 21 45 710 is distinguished by an indeed similarly unvarying or constant, but high coefficient of friction and is therefore particularly suitable as material for producing synchronising rings.

In addition to iron which inter alia already acts in a grain-fining manner, it is possible to admix with a copper/zinc alloy in accordance with the invention, as grain finer, slight additions, in each case not exceeding 0.05 percent, of the elements chromium, vanadium or titanium.

An alloy in accordance with the invention can be produced in accordance with processes which are customary for copper/zinc alloys. In this respect, it is initially preferably cast in semi- or fully-continuous continuous casting. Chill casting is, in this connection, not suitable, since in this respect the wear carriers coagulate and thus no uniform initial distribution of the intermetallic compounds would be ensured.

Subsequently the alloy is extruded and then drop-forged. By rapid cooling in quiescent or moving air after the forging, for instance from a temperature in the region between 600 and 7500C, the structure of an alloy in accordance with the invention occurs with about 60 to 85 percent amixed crystals, which are embedded in predominantly finely-dispersed distribution into the base matrix of mixed crystal. The intermetallic compounds are, in this respect, distributed in fine-grained formation statisticallyrandomly over the base matrix.

Depending upon the composition, more especially in the case of copper contents which lie at the lower boundary of the indicated alloying range, it can, to achieve the finest possible distribution of the a-mixed crystals or also to increase the proportion of the a-phase or for the furthur increase in the strength, in addition be favourable to carry out a final heat treatment of the material. This consists advantageously in a precipitation, acting as artificial aging, at a temperature between 1 50 and 350 , preferably at about 2500C. The duration of the heat treatment can, in this respect, vary between one hour and 20 hours and preferably be about 10 hours.

Claims

1. A copper/zinc alloy having a structure in which a constituent of cubic face centered a- mixed crystal is embedded into a base matrix of cubic body centered mixed crystal, characterised in that the alloy consists of 60 to 75 percent Cu, 6 to 8 percent Mn, 4 to 6 percent Al, 1 to 4 percent Si, 1 to 3 percent Fe, 0.5 to 1.5 percent Pb, up to 0.2 percent Ni, up to 0.2 percent Sn, the remainder being Zn, and has a structure in which 60 to 85 percent a-mixed crystals are embedded in predominantly finelydispersed distribution in the pphase.

2. A copper/zinc alloy as claimed in Claim 1, characterised in that the alloy has a structure in which approximately 65 to 70 percent a-mixed crystals are embedded in predominantly finelydispersed distribution in the phase.

3. A copper/zinc alloy as claimed in Claim 1 or 2, characterised in that the alloy contains over 70 percent, maximum 73 percent, Cu.

4. A copper/zinc alloy as claimed in any one of Claims 1 to 3, characterised in that the proportion of Ni and Sn in each case amounts to less than 0.05 percent.

5. A copper/zinc alloy as claimed in Claim 3, characterised by the following composition:

70.5 percent Cu

7.1 percent Mn

5.15 percent Al

1.5 percent Si

1.6 percent Fe 0.65 percent Pb 0.05 percent Ni 0.05 percent Sn Remainder Zn.

6. A copper/zinc alloy as claimed in any one of the preceding claims, characterised in that the alloy contains additions of up to 0.05 percent of one or more of the elements Cr, V or Ti.

7. Use of a copper/zinc alloy in accordance with any one of Claims 4 to 6 for a semi-finished product or semi-manufactured product which, in addition to good workability and high resistance to wear, has to have a uniform high coefficient of friction.

8. Use of a copper/zinc alloy in accordance with any one of Claims 4 to 6 for a synchronising ring.

9. A synchronising ring of a copper/zinc alloy in accordance with any one of Claims 4 to 6.