GB2123032A

GB2123032A - Copper-base alloys

Info

Publication number: GB2123032A
Application number: GB08317426A
Authority: GB
Inventors: Christopher Buchan
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1982-06-28
Filing date: 1983-06-27
Publication date: 1984-01-25
Also published as: GB2123032B; GB8317426D0

Abstract

Alloys, suitable for replacing cadmium copper and not requiring solution/precipitation heat treatment and which when hard drawn direct from the as-cast condition to the extent of 99.94% reduction in area, have a conductivity of at least 75% IACS and a product of conductivity expressed as % IACS and tensile strength expressed in MN/m<2> not less than 49,000 comprise: 0.05 to 0.2% tin; 0.05 to 0.25% magnesium; optionally up to 0.4% silver; optionally up to 0.01% phosphorus balance copper and impurities. <IMAGE>

Description

SPECIFICATION Copper-base alloys This invention relates to copper alloys of high strength and springiness, combined with relatively high electrical conductivity, such as may be used for railway electrification contact wires, telephone drop wires, tinsel conductors for flexible cables, small-conductor aircraft cables, current-carrying springs, connector and switch contacts and the like.

Currently the best available alloys of this class are the cadmium coppers, but in recent years the use of cadmium in industry has come to be suspected as entailing certain health hazards, and has been restricted in at least one country. Known alternatives require special solution/precipitation heattreatments to achieve comparable physical properties.

It is an object of the invention to provide a range of alloys that are acceptable as alternatives to cadmium copper without solution/precipitation heat-treatments and which are unlikely to present any significant health hazard.

In accordance with the invention, alloys exhibiting, when hard-drawn direct from the as-cast condition to the extent of 99.94% reduction in area, a conductivity of at least 75% IACS and a product of conductivity expressed as % IACS and tensile strength expressed in MN/m2 not less than 49,000 comprise: 0.05 to 0.2% tin; 0.05 to 0.25% magnesium; optionally up to 0.4% silver; balance copper and impurities.

Phosphorus is an acceptable impurity with a tolerance level of about 0.01%.

Preferred alloys in the defined condition achieve conductivity/tensile strengths products of about 50,000, and a product up to 55,000 or better can be achieved by drawing from a cold-worked-andannealed condition.

Silver has little effect on the properties of the alloy at room temperatures, but tends to increase their softening temperatures; when this benefit is required, a silver content of at least 0.03% is desirable.

The alloys of the invention can be fabricated by conventional techniques; when casting without a protective atmosphere, magnesium should be added as a master alloy and a small excess is needed to compensate for oxidation.

The invention will be further described, with reference to the table below and the accompanying drawings in which: Figure lisa composition diagram for the ternary copper-tin-magnesium alloys in accordance with the invention; and Figure 2 is a graph of tensile strength and conductivity against reduction in area for one alloy in accordance with the invention.

Experimental batches of six alloys (three in accordance with the invention and three for comparison) were prepared from cathode copper (or in one case from phosphorus-deoxidised copper) and high-purity tin and magnesium ingot. Melts were prepared by induction-heating in alumina crucibles under argon and cast into pre-heated carbo-dressed steel moulds to form cylindrical ingots 20 mm in diameter.

The castings were cold-rolled to 6 mm diameter and drawn to 0.5 mm wire using a reduction in area of about 22% per die (B 8 S die sequence). Total reduction in area was 99.94%.

The following table shows the compositions and selected properties (in this hard-drawn condition) of the examples, and their compositions are also shown in Figure 1 in which the quadrilateral PQRS defines the alloys of the invention: TABLE

Example Composition (balance copper) B 0.2% A Tensile AXB Proof Elongation Mg Sn P Conductivity Strength Stress % % % PPM %IACS MN/m X10 MN/m2 on 250 mm 1* - 0.1 1 87.7 524 46 495 1.5 2 0.09 0.1 1 83.6 599 50 558 2.2 3 0.15 0.1 1 80.6 621 50 594 2.7 4 0.16 0.1 70 78.5 642 50 820 2.4 5* - 0.27 1 79.4 606 48 565 2.5 6* 0.08 0.29 1 74.0 651 49 627 1.8 * for comparison Figure 2 is a graph showing conductivity and tensile strength as a function of the reduction in area for the alloy of Example 3 as a function of reductionin area from different initial conditions. Curves 1 and 2 relate to material drawn to the reduction in area indicated directly from cast ingot; curves 3 and 4 are corresponding curves for material first drawn to a reduction in area of 90%, annealed and further drawn to the extent plotted on the graph; curves 5 and 6 are corresponding curves for material similarly processed but with a first reduction in area of 99.5%.

It can be seen from the graphs that this type of dual cold working can secure very high tensile strengths, up to about 850 MN/m2 with only a modest loss of conductivity; by this means a conductivity-tensile strength product of up to around 64000 can be achieved. This corresponds to a product of around 65,000 for cadmium-copper comparably treated. Figure 2 also shows a tensile strength curve 7 for cadmium copper drawn to 95% reduction on area, annealed and re-drawn to the extent plotted, and it will be noted that this curve is closely approximated by the curve 5 relating to the alloy of the invention.

Claims

1. An alloy exhibiting, when hard drawn direct from the as-cast condition to the extent of 99.94% reduction in area, a conductivity of at least 75% IACS and a product of conductivity expressed as % IACS and tensile strength expressed in MN/m2 not less than 49,000 comprising 0.05 to 0.2% tin; 0.005 to 0.25% magnesium; up to 0.4% silver; balance copper and impurities.

2. An alloy exhibiting, when hard drawn direct from the as-cast condition to the extent of 99.94% reduction in area, a conductivity of at least 75% IACS and a product of conductivity expressed as % IACS and tensile strength expressed in MN/m2 not less than 49,000 comprising 0.05 to 0.2% tin: 0.05 to 0.25% magnesium; up to 0.4% silver: balance copper and impurities.

3. An alloy as claimed in Claim 2 in which the silver content is at least 0.03%.

4. An alloy as claimed in any one of the preceding claims in which phosphorus is present as an impurity at a level not exceeding 0.01%.

5. An alloy having a composition represented by a point within the quadrilateral PQRS in Figure 1.

6. The alloy of Example 2.

7. The alloy of Example 3.

8. The alloy of Example 4.

9. Hard drawn products made from the alloy claimed in any one of the preceding claims.

10. Hard drawn articles made from the alloy claimed in any one of Claims 1 to 6 by cold drawing, annealing, and cold drawing again.