Copper-nickel-zinc alloy containing silicon

Abstract

The invention includes a copper-nickel-zinc alloy with the following composition in weight %: Cu 47.0 to 49.0%, Ni 8.0 to 10.0%, Mn 0.2 to 0.6%, Si 0.05 to 0.4%, Pb 1.0 to 1.5%, Fe and/or Co up to 0.8%, the rest being Zn and unavoidable impurities, wherein the total of the Fe content and double the Co content is at least 0.1 weight % and wherein mixing silicides containing nickel, iron and manganese and/or containing nickel, cobalt and manganese are stored as spherical or ellipsoidal particles in a structure consisting of an - and -phase. The invention further relates to a method for producing semi-finished products from a copper-nickel-zinc alloy.

Claims

1. A copper-nickel-zinc alloy having the following composition, in % by weight: Cu 47.0 to 49.0%, Ni 8.0 to 10.0%, Mn 0.2 to 0.6%, Si 0.05 to 0.4%, Pb 1.0 to 1.5%, Fe and/or Co up to 0.8%, remainder Zn and unavoidable impurities, wherein a sum total of the Fe content and twice the Co content is at least 0.1%, mixed silicides containing nickel, iron and manganese and/or mixed silicides containing nickel, cobalt and manganese are incorporated as spherical or ellipsoidal particles in a microstructure consisting of and phase and an areal density of the silicides having a particle diameter of at most 1 m is at least 20 per 100 m.sup.2.

2. The copper-nickel-zinc alloy as claimed in claim 1, characterized in that either the Fe content or the Co content is at least 0.1% by weight.

3. The copper-nickel-zinc alloy as claimed in claim 1, characterized in a sum total of the Fe content and eight times the Co content is at least 0.4% by weight.

4. The copper-nickel-zinc alloy as claimed in claim 1 having the following composition, in % by weight: Cu 47.0 to 49.0%, Ni 8.0 to 10.0%, Mn 0.2 to 0.6%, Si 0.05 to 0.4%, Pb 1.0 to 1.5%, Fe 0.2 to 0.8%, remainder Zn and unavoidable impurities, optionally up to 0.8% Co, wherein mixed silicides containing nickel, iron and manganese are incorporated as spherical or ellipsoidal particles in a microstructure consisting of and phase.

5. The copper-nickel-zinc alloy as claimed in claim 4 having the following composition, in % by weight: Cu 47.0 to 49.0%, Ni 9.0 to 9.8%, Mn 0.3 to 0.4%, Si 0.1 to 0.3%, Pb 1.0 to 1.5%, Fe 0.4 to 0.6%, remainder Zn and unavoidable impurities, optionally up to 0.6% Co, wherein mixed silicides containing nickel, iron and manganese are incorporated as spherical or ellipsoidal particles in a microstructure consisting of and phase.

6. The copper-nickel-zinc alloy as claimed in claim 4, characterized in that a ratio of a sum total of proportions by weight of the elements Ni, Fe and Mn bound in silicides to a proportion by weight of the silicon bound in silicides is between 3 and 6.5.

7. The copper-nickel-zinc alloy as claimed in claim 6, characterized in that a of a sum total of proportions by weight of the elements Ni, Fe and Mn bound in silicides to a proportion by weight of the silicon bound in silicides is between 4 and 6.

8. The copper-nickel-zinc alloy as claimed in claim 4, characterized in that a ratio of a sum total of proportions by weight of the elements Ni and Fe bound in silicides to a proportion by weight of the manganese bound in silicides is at least 4.

Description

(1) Exemplary embodiments of the invention will be explained in more detail hereinbelow.

(2) For the investigations, three alloy compositions CA, CC and CD of an - nickel silver were cast in a Tammann furnace to form blocks measuring approximately 25 mm60 mm100 mm (see table 1).

(3) TABLE-US-00001 TABLE 1 Chemical composition in % by weight Cu Zn Ni Mn Si Pb Fe Co CA 48.6 40.5 9.3 0.4 1.2 CC 48.8 39.8 9.2 0.35 0.15 1.2 0.5 CD 48.6 39.9 9.3 0.35 0.15 1.2 0.5

(4) The cast blanks were then reduced by 45% in a plurality of rolling passes at 750 C. Metal sheets having a thickness of 6 mm which were prepared therefrom by milling on both sides were subjected to cold rolling to 4 mm, and then to soft annealing at 650 C. for three hours. Then, these metal sheets were subjected to cold rolling to 2.88 mm, then to renewed annealing at 650 C. for three hours and to cold rolling to an end thickness of 2.0 mm. Finally, the strips were subjected to stress-relief annealing at 300 C.

(5) Table 2 shows the mechanical properties achieved after the annealing at 300 C.:

(6) TABLE-US-00002 TABLE 2 Mechanical properties of the alloys Rp0.2/ HV10 MPa Rm/MPa A5/% CA 202 582 658 23 CC 242 712 769 6 CD 247 752 788 10

(7) The silicon-containing variants CC and CD are harder and achieve higher strength values than the comparative material CA. Accordingly, micrographs illustrating the microstructure of the alloys CC and CD show a much finer-grained microstructure than the micrographs illustrating the microstructure of the silicon-free alloy CA. The gain in mechanical strength is explained by the formation of fine silicides: in a scanning electron microscope, small spherical and ellipsoidal precipitations are identifiable in the alloys CC and CD.

(8) The local element composition of the phase, the phase and the silicides was determined for the variants CC and CD by means of energy dispersive X-ray analysis in a scanning electron microscope.

(9) For the variant CC, the approximate weight ratios Cu:Zn=1.3:1 and Cu:Ni=5:1 are obtained for the phase. In the phase, the weight ratios are approximately Cu:Zn 0.9:1 and Cu:Ni=3:1 to 4:1. For the silicides, the energy dispersive X-ray analysis supplies a composition of the elements Cu, Zn, Ni, Mn, Si and Fe each in significant proportions. Beyond the silicides, proportions of less than 0.4% by weight are obtained for the elements Mn, Si and Fe. On account of the small size of the silicides, the high proportions of Cu and Zn in the X-ray signal for the silicides come from the environment in which the silicide is embedded. They effectively represent the background signal of the matrix. The signals for Cu and Zn in this respect are present very precisely in the ratio obtained for the pure phase or the pure phase. The X-ray signal for the element Ni is composed of the signal of the nickel bound in the silicide and the background signal of the nickel in the CuNiZn matrix. The contribution of the nickel background signal can be determined from the local Cu content with the aid of the information relating to the phase ( or ) and the Cu:Ni ratio corresponding to the phase and can be subtracted from the total Ni signal. The nickel content of the silicide determined in this way can then be related with the elements Mn, Fe and Si. If the background signal represents a contribution of more than 50% of the total nickel signal, the declaration made in relation to the nickel content in the silicide is fraught with uncertainty. Using this method, values of between 4 and 5.7 were ascertained for the weight ratio (Ni+Fe+Mn)/Si in the silicide. The weight ratio (Ni+Fe)/Mn always assumes values of greater than 4.

(10) The number of silicides per unit of area was determined with reference to the scanning electron microscope images. For the variant CC, at least 20 particles having a diameter of smaller than 1 m were ascertained over 100 m.sup.2.

(11) For the variant CD, too, the approximate weight ratios Cu:Zn=1.3:1 and Cu:Ni=5:1 are obtained for the phase from the energy dispersive X-ray analysis. In the phase, the weight ratios are approximately Cu:Zn=0.9:1 and Cu:Ni=3:1 to 4:1. For the silicides, the X-ray analysis supplies a composition of the elements Cu, Zn, Ni, Mn, Si and Co each in significant proportions. Beyond the silicides, proportions of less than 0.4% by weight are obtained for the elements Mn, Si and Co. As in the case of variant CC, the X-ray signal for the silicides contains high proportions of Cu and Zn. On account of the small size of the silicides, these proportions are interpreted as a background signal of the matrix in which the silicide is embedded. The signals for Cu and Zn in this respect are present very precisely in the ratio obtained for the pure phase or the pure phase. As described in the case of variant CC, the X-ray signal for the element Ni was adjusted by the contribution of the background signal of the nickel in the CuNiZn matrix, and the nickel content of the silicide determined in this way was then related with the elements Mn, Co and Si. Using this method, values of between 2.5 and 4.5 were ascertained for the weight ratio (Ni+Co+Mn)/Si in the silicide. The weight ratio (Ni+Co)/Mn always assumes values of greater than 10. Furthermore, the ratio of the nickel bound in silicides to the cobalt bound in silicides always assumes values of between 1.5 and 2.5.

(12) The number of silicides per unit of area was determined with reference to the scanning electron microscope images. For the variant CD, at least 20 particles having a diameter of smaller than 2 m were ascertained over 5000 m.sup.2.

(13) In order to reconstruct wire production, the pure metals copper, zinc, nickel and lead were melted together with a corresponding quantity of binary prealloys of copper and iron, copper and silicon and copper and manganese in a medium-frequency furnace and cast in stationary steel molds with a diameter of 220 mm. In preparation for the extrusion of wires, the oxidized surfaces of the solidified cylindrical cast blocks were removed by cutting. With the aid of an extruder, cast blocks having a length of 500 mm were pressed to form wires having a diameter of 4 mm. The chemical composition of a pressed wire was analyzed in a wet chemical process by ICP-OES (figures in % by weight):

(14) TABLE-US-00003 Cu Zn Ni Mn Si Pb Fe Co Pressed 48.4 39.6 9.5 0.36 0.32 1.3 0.49 0.01 wire

(15) The melting point of the alloy is approximately 850 C. After the extrusion, the wire was subjected to a heat treatment at 800 C. and then quenched. Forming with a degree of deformation of 28% was effected by cold rolling the wire to a wire thickness of 3 mm. After the cold forming, the hardness was 175 HV 10. Age annealing for three hours at temperatures of between 350 C. and 500 C. hardened the material, this being expressed in hardness values of up to 207 HV 10. This increase in the strength is explained by the formation of silicides of the elements still in solution during the age annealing.