Copper alloy and process for obtaining same

Abstract: A copper base alloy consisting essentially of tin in an amount from about 0.1 to about 1.5% by weight, phosphorous in an amount from about 0.01 to about 0.35% by weight, iron in an amount from about 0.01 to about 0.8% by weight, zinc in an amount from about 1.0 to about 15% by weight, and the balance essentially copper, including phosphide particles uniformly distributed throughout the matrix, is described. The alloy is characterized by an excellent combination of physical properties. The process of forming the copper base alloy described herein includes casting, homogenizing, rolling, process annealing and stress relief annealing.

Description: The present invention relates to a process for preparing copper base alloys having utility in electrical applications. There are a number of copper base alloys that are used in connector, lead frame and other electrical applications because their special properties are well suited for these applications. Despite the existence of these alloys, there remains a need for copper base alloys that can be used in applications that require high yield strength greater than of 56,25 kg/mm 2 (80 KSI), together with good forming properties that allow one to make 180° badway bends with a R/T ratio of I or less plus low relaxation of stress at elevated temperatures and freedom of stress corrosion cracking. Alloys presently available do not meet all of these requirements or have high costs that make them less economical in the marketplace or have other significant drawbacks. It remains highly desirable to develop a copper base alloy satisfying the foregoing goals. Beryllium copper generally has very high strength and conductivity along with good stress relaxation characteristics; however, these materials are limited in their forming ability. One such limitation is the difficulty with 180° badway bends. In addition, they are very expensive and often require extra heat treatment after preparation of a desired part. Naturally, this adds even further to the cost. Phosphor bronze materials are inexpensive alloys with good strength and excellent forming properties. They are widely used in the electronic and telecommunications industries. However, they tend to be undesirable where they are required to conduct very high current under very high temperature conditions, for example under conditions found in automotive applications for use under the hood. This combined with their high thermal stress relaxation rate makes these materials less suitable for many applications. High copper, high conductivity alloys also have many desirable properties, but generally do not have mechanical strength desired for numerous applications. Typical ones of these alloys include, but are not limited to, copper alloys 110, 122, 192 and 194. Representative prior art patents include U.S. Patents 4,666,667, 4,627,960, 2,062,427, 4,605,532, 4,586,967, 4,822,562, and 4,935,076. JP 6299275, JP 6184679 and JP 62116745 disclose several type of such alloys. Accordingly, it is highly desirable to develop copper base alloys having a combination of desirable properties making them eminently suitable for many applications. In accordance with the present invention, it has been found that the foregoing objective is readily obtained. Copper base alloys prepared in accordance with the present invention as defined in claim 1 comprise tin in an amount from about 0.1 to about 1.5%, preferably from about 0.4 to 0.9%, phosphorous in an amount from about 0.01 to about 0.35%, preferably from about 0.01% to about 0.1%, iron in an amount from about 0.01% to about 0.8%, preferably from about 0.05% to about 0.25%, zinc in an amount from about 1.0 to about 15%, preferably from about 6.0 to about 12.0%, and the balance copper and unavoidable impurities, said alloy including phosphide particles uniformly distributed throughout the matrix, said phosphide particles including a finer component made up of phosphide particles having a size in the range of from 50 to 250 Angstroms and a coarser component made up of phosphide particles having a size in the range of from 0.075 to 0.5 microns, and said fine and coarse particles being present in an amount and distribution sufficient to cause said alloy to have a 180° bad-way bend with a R/T ratio of 1 or less. It is particularly advantageous to include nickel and/or cobalt in an amount up to about 0.5% each, preferably in an amount from about 0.001% to about 0.5% each. Alloys may also include up to 0.1% each of aluminum, silver, boron, beryllium, calcium, chromium, indium, lithium, magnesium, manganese, lead, silicon, antimony, titanium, and zirconium. As used herein, the percentages are weight percentages. It is desirable and advantageous in the alloys prepared according to the process the present invention to provide phosphide particles of iron and/or nickel and/or magnesium or a combination thereof, uniformly distributed throughout the matrix since these particles serve to increase strength, conductivity, and stress relaxation characteristics of the alloys. The phosphide particles have a particle size of 50 Angstroms to about 0.5 microns-and include a finer component and a coarser component. The finer component has a particle size ranging from about 50 to 250 Angstroms, preferably from about 50 to 200 Angstroms. The coarser component has a particle size generally from 0.075 to 0.5 microns, preferably from 0.075 to 0.125 microns. The alloys prepared according to the process of the present invention enjoy a variety of excellent properties making them eminently suitable for use as connectors, lead frames, springs and other electrical applications. The alloys should have an excellent and unusual combination of mechanical strength, formability, thermal and electrical conductivities, and stress relaxation properties. The process of the present invention comprises: casting a copper base alloy having a composition as aforesaid; homogenizing at least once for at least one hour at temperatures from about 537,8 to 787,8°C (1000 to 1450°F); rolling to finish gauge including at least one process anneal for at least one hour at 343,3 to 648,9°C (650 to 1200°F); and stress relief annealing for at least one hour at a temperature in the range of 148,9 to 315,6°C (300 to 600°F), thereby obtaining a copper alloy including phosphide particles uniformly distributed throughout the matrix. Nickel and/or cobalt may be included in the alloy as above. The alloys prepared according to the process of the present invention are modified copper-tin-zinc alloys. They are characterized by higher strengths, better forming properties, higher conductivity, and stress relaxation properties that represent a significant improvement over the same properties of the unmodified alloys. The alloys prepared according to the process of the present invention include those copper base alloys comprising tin in an amount from about 0.1 to 1.5%, preferably from about 0.4 to about 0.9%, phosphorous in an amount from about 0.01 to about 0.35%, preferably from about 0.01 to about 0.1%, iron in an amount from about 0.01 to about 0.8%, preferably from about 0.05 to about 0.25%, zinc in an amount from about 1.0 to about 15%, preferably from about 6.0 to about 12.0%, and the balance copper and unavoidable impurities. These alloys typically have phosphide particles uniformly distributed throughout the matrix, said phosphide particles including a finer component made up of phosphide particles having a size in the range of from 50 to 250 Angstroms and a coarser component made up of phosphide particles having a size in the range of from 0.075 to 0.5 microns, and said fine and coarse particles being present in an amount and distribution sufficient to cause said alloy to have a 180° bad-way bend with a R/T ratio of 1 or less. These alloys may also include nickel and/or cobalt in an amount up to about 0.5% each, preferably from about 0.001 to about 0.5% of one or combinations of both. One may include one or more of the following elements in the alloy combination: aluminum, silver, boron, beryllium, calcium, chromium, indium, lithium, magnesium, manganese, lead, silicon, antimony, titanium, and zirconium. These materials may be included in amounts less than 0.1%, each generally in excess of 0.001 each. The use of one or more of these materials improves the mechanical properties such as stress relaxation properties; however, larger amounts may affect conductivity and forming properties. The aforesaid phosphorous addition allows the metal to stay deoxidized making it possible to cast sound metal within the limits set for phosphorous, and with thermal treatment of the alloys, phosphorous forms a phosphide with iron and/or iron and nickel and/or iron and magnesium and/or a combination of these elements, if present, which significantly reduces the loss in conductivity that would result if these materials were entirely in solid solution in the matrix. It is particularly desirable to provide iron phosphide particles uniformly distributed throughout the matrix as these help improve the stress relaxation properties by blocking dislocation movement. Iron in the range of about 0.01 to about 0.8% and particularly about 0.05 to about 0.25% increases the strength of the alloys, promotes a fine grain structure by acting as a grain growth inhibitor and in combination with phosphorous in this range helps improve the stress relaxation properties without negative effect on electrical and thermal conductivities. Nickel and/or cobalt in an amount from about 0.001 to 0.5% each are desirable additives since they improve stress relaxation properties and strength by refining the grain and through distribution throughout the matrix, with a positive effect on the conductivity. The process of the present invention as defined in claim 1 includes casting an alloy having a composition as aforesaid. Any suitable casting technique known in the art such as horizontal continuous casting may be used to form a strip having a thickness in the range of from about 12,70 to 19,05 mm (0.500 to 0.750 inches). The processing includes at least one homogenization for at least one hour, and preferably for a time period in the range of from about I to about 24 hours, at temperatures in the range of from about 537,8 to 787,8°C (1000 to 1450°F). At least one homogenization step may be conducted after a rolling step. After homogenization, the strip may be milled once or twice to remove from about 0,508 to 2,54 mm (0.020 to 0.100 inches)of material from each face. The material is then rolled to final gauge, including at least one process anneal at 343,3 to 648,9°C (650 to 1200°F) for at least one hour and preferably for about 1 to 24 hours, followed by slow cooling to ambient at 11,1 to 111,1°C (20 to 200°F) per hour. The material is then stress relief annealed at final gauge at a temperature in the range of 148,9 to 315,6°C (300 to 600°F) for at least one hour and preferably for a time period in the range of about 1 to 20 hours. This advantageously improves formability and stress relaxation properties. The thermal treatments provide the alloys prepared according to the process of the present invention with phosphide particles of iron and/or nickel and/or magnesium or a combination thereof uniformly distributed throughout the matrix. The phosphide particles increase the strength, conductivity, and stress relaxation characteristics of the alloys. The phosphide particles have a particle size of about 50 Angstroms to about 0.5 microns and include a finer component and a coarser component. The finer component has a particle size of about 50 to 250 Angstroms, preferably from about 50 to 200 Angstroms. The coarser component has a particle size generally from 0.075 to 0.5 microns, preferably from 0.075 to 0.125 microns. Alloys formed in accordance with the process of the present invention and having the aforesaid compositions are capable of achieving a yield strength in the 56,25 to 70,31 kg/mm 2 (80-100 KSI) range with bending ability at a radius equal to its thickness, badway, on a width up to 10 times the thickness. Additionally, they are capable of achieving an electrical conductivity of the order of 35% IACS, or better. The foregoing coupled with the desired metallurgical structure should give the alloys a high stress retention ability, for example over 60% at 150°C, after 1000 hours with a stress equal to 75% of its yield strength on samples cut parallel to the direction of rolling, and makes these alloys very suitable for a wide variety of applications requiring high, stress retention capabilities. Moreover, the present alloys do not require further treatment by stampers. The present process of the invention may include two homogenization steps, wherein at least one homogenization step is subsequent to a rolling step and wherein the homogenization steps are for 2 to 24 hours each. The casting step may comprise casting a copper base alloy comprising tin in an amount from 0.4 to 0.9% by weight, zinc in an amount from 6.0 to 12.0% by weight, phosphorous in an amount from 0.01 to 0.2% by weight, iron in an amount from 0.01 to 0.8% by weight, a material selected from the group consisting of nickel, cobalt and mixtures thereof in an amount from 0.001 to 0.5% by weight each, and the balance copper and unavoidable impurities.

Claims: A process for preparing a copper base alloy which comprises: casting a copper base alloy comprising tin in an amount from 0.1 to 1.5% by weight, phosphorous in an amount from 0.01 to 0.35% by weight, iron in an amount from 0.01 to 0.8% by weight, zinc in an amount from 1.0 to 15% by weight, and the balance copper and unavoidable impurities; homogenizing at least once for at least one hour at a temperature from 537,8 to 787,8°C (1000 to 1450°F); rolling to final gauge including at least one process anneal for at least one hour at 343,3 to 648,9°C (650 to 1200°F) followed by slow cooling at a rate of 11,1 to 111,1°C (20 to 200°F) per hour; and stress relief annealing at final gauge for at least one hour at 148,9 to 315,6°C (300 to 600°F), thereby obtaining a copper base alloy including phosphide particles uniformly distributed throughout the matrix, said phosphide particles including a finer component made up of phosphide particles having a size in the range of from 50 to 250 Angstroms and a coarser component made up of phosphide particles having a size in the range of from 0.075 to 0.5 microns. Process according to claim 1, wherein said copper base alloy being cast includes a material selected from the group consisting of nickel, cobalt and mixtures thereof in an amount from 0.001 to 0.5% by weight each, at the expense of copper. Process according to claim 1 or 2, wherein said copper base alloy being cast includes magnesium and said phosphide particles are selected from the group consisting of iron nickel phosphide particles, iron magnesium phosphide particles, iron phosphide particles, magnesium nickel phosphide particles, magnesium phosphide and mixtures thereof. Process according to claim 1, including two homogenization steps, wherein at least one homogenization step is subsequent to a rolling step and wherein the homogenization steps are for 2 to 24 hours each. Process according to claim 1, wherein said process anneal is for 1 to 24 hours. Process according to claim 1, wherein said stress relief anneal is for 1 to 20 hours. Process according to claim 1, wherein said casting step forms a strip having a thickness from 12,70 to 19,05 mm (0.500 to 0.750 inches) and said process further includes milling said strip at least once following said at least one homogenizing step. Process according to claim 1, wherein said casting step comprises casting a copper base alloy comprising tin in an amount from 0.4 to 0.9% by weight, zinc in an amount from 6.0 to 12.0% by weight, phosphorous in an amount from 0.01 to 0.2% by weight, iron in an amount from 0.01 to 0.8% by weight, a material selected from the group consisting of nickel, cobalt and mixtures thereof in an amount from 0.001 to 0.5% by weight each, and the balance copper and unavoidable impurities.

Inventors: BHARGAVA ASHOK K, BHARGAVA, ASHOK K.
Applicants: WATERBURY ROLLING MILLS INC, WATERBURY ROLLING MILLS, INC.
Application year: 1998
Main classification: C22C9
IPC codes: C22F1, C22C9, H01B1