GB2051127A

GB2051127A - Precipitation hardening copper alloys

Info

Publication number: GB2051127A
Application number: GB8014065A
Authority: GB
Original assignee: DELTA ENFIELD METALS
Current assignee: DELTA ENFIELD METALS
Priority date: 1979-04-30
Filing date: 1980-04-29
Publication date: 1981-01-14
Also published as: NO154019B; IE800880L; NO154019C; AU521823B2; JPS55158246A; ZA802595B; DK186080A; AU5793080A; NO801272L; JPS633938B2; EP0018818A1; IE49710B1; GB2051127B

Description

SPECIFICATION Precipitation hardening copper alloys

V GB 2 051 127 A 1 This invention relates to precipitation and dispersion hardening copper alloys and more particularly to precipitation hardening copper alloys that combine good mechanical and electrical properties.

There are many applications in which a strong resilient part having good electrical conductivity is desired. Due to its excellent conductivity, copper would be an ideal metal to use were it not for its relatively poor mechanical properties such as comparative softness, low modulus of elasticity and low tensile and tensile yield strengths.

Unlike many kinds of steel, most copper alloys are not susceptible to improvement in hardness and strength by heat treatment processes. One useful exception to this is the copper-beryllium alloys which 10 are precipitation or age hardenable. These copper alloys, typically containing between 1 and 2% beryllium, are useful because of their non magnetic properties, good electrical conductivity, high tensile strength, high degree of hardness, and their ability to be cast, wrought, forged or drawn. Because of these properties they find utility in the manufacture of various types of scientific instruments, electrical contact points, coil springs, non magnetic cutting tools and the like.

While copper beryllium alloys have useful mechanical and electrical properties, their cost is comparatively high due to the scarceness of beryllium in the earth's crust. Of even greater concern, however is that it is now recognized that beryllium is an extremely toxic material and is a hazardous carcinogen. This makes in difficult to process copper beryllium alloys with conventional techniques without creating danger to the health of workers and without violating exposure standards as set by various governmental health organisations. Copper-beryllium alloys present a health hazard not only at the time of manufacturing the alloy, but also in subsequent operations which give rise to air borne metallic oxide dust particles.

Other copper base alloys also tend to be deficient in certain respects. For example, brasses, phosphor bronzes, nickel silvers and most copper alloys obtain their property increases through cold.

working, which decreases formability in proportion to the amount of cold work. Other dispersion hardening alloys have insufficient electrical conductivity to be useful in electrical applications. This invention provides a beryllium-free precipitation hardenable copper alloy that has mechanical and electrical properties similar to those ordinarily only obtained with copper-beryllium alloys. 30 The copper alloys of the invention combine useful properties of tensile strength, yield strength, hardness, formability, corrosion resistance and resistance to fatigue, and electrical conductivity. According to the invention, a copper-nickel alloy includes minor quantities of silicon, chromium and aluminum. To achieve the desired mechanical properties at least 2% nickel is required and the practical upper limit from the stand point of electrical conductivity is 9%. The silicon, chromium and aluminum are all essential, at least in small amounts, of from 0.05% to 2%. Within these limits, a large number of alloys can be made. No specific percentages can be given as ideal since, as is so often the case, an increase or decrease in a particular component is a trade off of one desirable property for another and the exact formulation selected will depend on the end use requirements.-rhe total amount of silicon, aluminum and chromium, however, preferably does not exceed 2%. A typically useful alloy with a good average 40 range of properties comprises 4.5% nickel, 0.5 to 0.7% aluminum and silicon and 0.25% chromium. It may also be desirable to add trace amounts (i.e. up to 0.0 1 %) of incidental elements such as lithium, boron or phosphorous for deoxidizing or fluidity purposes.

Generally speaking, depending upon the end use application, it is desired to provide a conductivity of at least 8.1 x 101 Sm-1 (14% I.A.C.S. (International Association of Conductivity Standards).

The alloys of this invention have a very complex structure of the various pseudo-binary systems with copper as the base component and the other elements combined in various combinations as the other phases. The alloy has increased solubility at elevated temperatures and this alpha state can be maintained by rapidly quenching to room temperature, thereby creating an unstable, super saturated condition that only requires the proper temperature to precipitate the hardening phases.

The alloys of this invention are readily hardenable, which is a time/temperature related function. For example, maximum hardness can be obtained in less than 2 hours if the alloys are heated to about 4000C., but, this time can be reduced to only about 15 seconds at a temperature of about 7501C.

The variation of various properties of the alloys of the invention with changing constitution is 55 illustrated in the drawings of which:- Fig. 1 is a graph showing the effect upon ultimate tensile strength and conductivity when the nickel content of an alloy of this invention is varied as shown along the abscissa and the alloying amount of Si and Al are held constant at 0.75 % and the Cr at 0.5 %.

Fig. 2 is a graph showing the effect upon ultimate tensile strength and conductivity when the aluminum content of an alloy of this invention is varied as shown along the abscissa and the Ni is held 60 constant at 5%, the Si at 0.75%, and the Cr at 0.5%.

Fig. 3 is a graph showing the effect upon ultimate tensile strength and conductivity when the silicon content of an alloy of this invention is varied as shown along the abscissa and the Ni is held constant at 5%, the AI at 0.75% and the Cr at 0.5%.

2 GB 2 051 127 A 2 Fig. 4 is a graph showing the effect upon ultimate tensile strength and conductivity when the chromium content of an alloy of this invention is variedas shown along the abscissa and the Ni content is held constant at 5% and the AI and Si at 0.75%.

Fig. 5 is a graph showing the time required to achieve maximum hardness of typical alloys of this 5 invention plotted against the function of temperature.

Table 1 shows typical property values of the alloys according to the invention.

TABLE 1

Unaged Aged DENSITY gMICM3 at 200C 8.694 8.681 lb/in 3 at68OF 0.3140 0.3136 SPECIFIC J/(kg. OK) 397 397 HEAT CAPACITY BtU/(ib 'F) 0.0948 0.0948 THERMAL W/(m.k) 78.9 78.9 CONDUCTIVITY BtU ft "h -F -1 45.6 45.6 (0-200OC) c al cm S C 0.188 0.188 MODULUS OF lbf/in 2 X 106 ELASTICITY kPa x 106 17-19 17-19 117.2-131.0 117.2-131.0 MAGNETIC PERMEABILITY mOe 1.001 1.005 1.001 (HM -1) x 10 -9 1.257 1.262 1.257 ELECTRICAL CONDUCTIVITY % JACS 12 18-20 SM-1 X 1.06 7.0 10.4-11.6 VOLUME RESISTIVITY (at 20OC) 9 (circ millft) 88 53-69 9 m 146.3 88.1-114.7 MAXIMUM TEMPS (stable for 24 hours) 375C 3750C 707 " F 70717 The following examples illustrate the invention. In the examples, alloys having the constitution shown in Table 11 were made in accordance with this invention using standard techniques. Table Ill shows the variation in properties obtained for the 10 alloys of Table 11. The property data listed was obtained after heat ageing at 4501C for the times shown.

3 GB 2 051 127 A 3 T TABLE 11

Alloy No. NM SM AM c 10/0 1 5.60 0.72 1.46 0.46 2 5.44 0.97 1.00 0.50 -3 5.81 0.79 0.28 0.44 4 5.52 0.74 0.77 0.22 5.54 0.89 0.78 0.33 6 5.35 1.41 0.82 0.40 7 5.23 1.41 0.83 0.42 8 5.44 1.30 0.80 0.42 9 5.30 0.28 0.72 0.36 2.15 0.88 0.78 0.46 11 3.18 0.90 0.77 0.41 12 4.55 0.95 0.86 0.41 13 4.23 1.02 0.92 0.47 14 8.63 1.31 1.16 0.20 7.88 1.42 1.23 0.18 16 7.11 1;36 0.86 0.21 17 7.89 1.38 0.01 0.19 18 5.37 0.86 0.78 0.43 19 5.20 0.80 0.80 0.40 3.27 0.88 0.81 0.44 21 7.67 1.25 1.15 0.19 22 -5.14 0.89 0.70 0.41 TABLE Ill

Alloy Optimum 0.1% Proof Stress 0.2% Proof Stress U. T. S. Elongation % Response to Ageing Conductivity Ageing (% I.A.C.S.) Time No. (Mins) psi x103 Pax-106 psi X 103 106 psi X 103 Pa x 106 (on 250 mm) psi x 10' Pa x 10 % IACS SM 1X106 Pa x 1 16 141 972 159 1096 176 1214 0.5 37 225 14.50 8.4 2 20 126 869 144 993 155 1069 0.25 37 225 16.27 9.2 3 20 116 800 131 903 133 917 0.5 28.5 197 20.02 11.6 4 45 99 683 ill 765 123 848 1.75 17.5 121 18.47 10.7 22 138 952 153 1055 161 1110 0.25 33 228 16.70 9.7 6 10 132 910 156 1076 182 1255 0.1 27.5 190 13.18 7.6 7 22 129 889 148 1020 165 1138 0.25 28 193 14.44 9.4 8 25 119 821 135 931 149 1027 0.25 36.5 252 17.47 10.1 9 60 93 641 96 662 0.25 10 69 18.08 10.5 45 125 862 141 972 154 1062 0.75 35 241 20.00 11.6 11 40 106 731 121 834 137 945 1,5 31.5 217 19.65 11.4 12 30 102 703 116 800 133 917 1.0 27.5 190 18.53 10.7 13 16 100 690 -116 800 129 889 0.5 18 124 16.28 9.4 14 20 159 1096 177 1220 188(201) 1296(1386 0.1 42.5 293 15.23 8.8 30 136 938 154 1062 168 1158 0.5 27.5 190 15.91 9.2 16 15 119 820 139 952 159 1096 30.5 21 0 17.33 10.0 17 5 156 1076 170 1172 179 1234 0.25 32.5 224 19.27 11.2 18 51 124 855 139 958 143 986 35.5 245 19.23 11.2 1G 102 703 118 814 134 924 1.5 32 221 18.24 10.6 40 104 717 118 814 132 910 1.5 32 221 19.35 11.2 21 10 138 952 170 1172 175 1207 0.25 30 207 15.11 8.8 22 22 125 862 140 965 148 1020 0.25 40 276 17.99 10.4 Tensile specimen fractures outside its gauge length. Reached on subsequent Tensile Tests.

J. I', -p, r-i 1, GB 2 051 127 A 5

Claims

1. A precipitation hardenable copper alloy comprising 2 to 9 weight percent nickel 0.05 to 2 weight percent of aluminium, chromium and silicon, the balance being copper and impurities.

2. A precipitation hardenable copper alloy according to claim 1, wherein the total amount of silicon, aluminum and chromium does not exceed 2% by weight. 5

3. A precipitation hardenable copper alloy according to claim 1, comprising substantially 4.6^ weight percent nickel, substantially 0.5 to 0.7 weight percent each silicon and aluminum and substantially 0.25 weight percent chromium, the balance being copper and impurities.

4. A precipitation hardenable copper alloy according to any one of claims 1 to 3 of which the conductivity after heat ageing is at least 8.1 X 101 Sm-1 (14% I.A.C.S.).

5. A precipitation hardenable copper alloy according to any one of claims 1 to 4 of which the ultimate tensile strength after heat ageing is in excess of 620 x 106 Pa (90,000 psi).

6. A precipitation hardenable copper alloy according to any one of claims 1 to 5 in which the impurities include trace amounts of conventional deoxidizers and fluidity improving agents.

7. A precipitation hardenable copper alloy substantially as described herein with reference to 15 Table 1.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1981. Published by the Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.