PRODUCTION OF COPPER-BERYLLIUM ALLOYS

Abstract: A process for producing beryllium-copper alloys is disclosed, which comprises the steps of obtaining a cast ingot by melting an alloy essentially consisting of from 0.05 to 2.0% by weight of Be, from 0.1 to 10.0% by weight of at least one kind of Co and Ni, and the balance being substantially Cu, subjecting the thus obtained cast ingot to a solution treatment at a temper­ ature range from 800 to 1,000°C, cold working, annealing at a temperature range from 750 to 950°C being lower than the solution treating temperature, and then an age hardening treatment. The alloy may further contain from 0.05 to 4.0% by weight of at least one kind of Si, Al, Mg, Zr, Sn, and Cr in a total amount. By this producing process, the beryllium-copper alloys having higher strength and formability can be obtained due to uniform and fine dispersion of solid-unsolved precipitate.

Description: The present invention relates to beryllium-copper alloys which have high electrical conductivity and high strength and which are used as connectors, relays, etc. More particularly, the invention relates to a process for producing beryllium-copper alloys which possess excellent strength and formability. A variety of beryllium-copper alloys have been widely used as wrought materials for electronic parts, etc. making the most of their characteristics of high electrical conductivity and high strength. In the production of these beryllium-copper alloys, as shown in the flow chart of Fig. 3, a cast ingot consisting of Cu, Be and other auxiliary component or components is obtained, is subjected to a solution treatment, for instance, at 750 to 950°C, is cold worked, and then is age hardened, thereby obtaining a desired beryllium-copper alloy. However, in the conventional production of the alloys mentioned above, the solution treatment is performed to improve strength and formability with a solid-unsolved intermetallic compound formed between Be and an auxiliary additive component or components. A large amount of coarse solid-unsolved precipitate of, for example, not less than 0.3 µm size is recognized in the beryllium-copper alloys which have undergone the above solution treatment. Thus, there is a problem that strength or formability cannot fully be improved. Strength can be increased in this case by solid-soliving a part of the solid-unsolved precipitates through merely raising a solution treating temperature. However, since the grain size in a matrix simultaneously becomes greater, this technique has a defect that a great problem of formability arises. US-A-4179314 describes a treatment process for beryllium-copper alloys consisting of a first solution heat treatment at 815-982°C, quenching, cold working, a second heat treatment at the same temperature as the first, quenching and two age-hardening treatments. It is an object of the present invention to overcome the above-mentioned problems. The invention provides a process for producing beryllium-copper alloys which have improved uniformity and increased strength and workability by making finer a large part of the conventionally coarse solid-unsolved precipitate preferably down to 0.3 µm or less and dispersing them into a matrix. The present invention also provides a process for producing beryllium-copper alloys, which can attain high strength and formability, by restraining grain growth during annealing due to the presence of solid-unsolved precipitate uniformly and finely dispersed in the matrix. The invention is set out in claim 1. The ingot may be obtained by melting an alloy. For a better understanding of the invention, reference is made to the attached drawings, wherein: Fig. 1 is a flow chart illustrating a process for producing beryllium-copper alloys according to the present invention; Figs. 2(a), (b), (c) and (d) are optical microscopic photographs of metallic structures of beryllium-copper alloys produced by a conventional process and by the process of the invention; and Fig. 3 is a flow chart illustrating an example of a conventional process for producing beryllium-copper alloys. In the present invention, a main reinforcing mechanism is precipitation of intermetallic compounds among Be and Co or Ni or further additives such as Si, Al, Mg, Zr, Sn and Cr. First, large precipitated grains are solid-solved into a matrix by the solution treatment at a temperature range from 800 to 1,000°C, above the conventional range, so that precipitating nuclei may readily be formed by cold working. Then, a cold worked product is annealed in a temperature range from 750 to 950°C, which is lower than the solution treating temperature, the difference between the annealing temperature and the solution treating temperature being in a range from 20 to 200°C, thereby obtaining an alloy in which a part of a solute is precipitated and consequently the precipitate of grain size of 0.3 µm or less may be present in an amount of not less than 40% of all the precipitated grains in a dispersed state. When at least one of Si, Al, Mg, Zr, Sn and Cr is incorporated into the alloy, the percentage of the precipitate having a grain size of not more than 0.3 µm may be not less than 50%. The reason why the added amount of Be is limited to from 0.05 to 2.0% by weight is that if it is less than 0.05% by weight, an effect due to its addition cannot be obtained, while if it is more than 2.0% by weight, cost rises for improved strength. The added amount is preferably from 0.1 to 0.7% by weight. The reason why at least one of Co and Ni is limited to 0.1 to 10% by weight is that if it is less than 0.1% by weight, an effect due to the addition cannot be obtained, while if it is over 10.0% by weight, formability becomes poorer and further improvement in the properties cannot be expected. The added amount is preferably from 0.2 to 4.0% by weight. The reason why the total added amount of at least one of Si, Al, Mg, Zr, Sn and Cr is limited to from 0.05 to 4.0% by weight is that if it is less than 0.05% by weight, an effect due to the addition cannot be obtained, while if it is over 4.0% by weight, formability becomes poorer and further improvement in the properties cannot be expected. Furthermore, the reason why the solution treating temperature is limited to from 800 to 1,000°C is that if it is less than 800°C, solid-solving of the precipitated grains does not proceed, while if it is over 1,000°C, the temperature becomes near or not less than a melting point of the alloy to render the production difficult. The annealing temperature depends upon the solution treating temperature, the strength required, and the grain size of crystals. However, if the annealing temperature is less than 750°C, an amount of precipitates during the annealing becomes greater and the strength after the age hardening lowers, while if it is over 950°C, the precipitate amount becomes smaller so that a refining effect of the grains in the matrix is lost. Thus, the annealing temperature is limited to from 750 to 950°C. Fig. 1 is a flow chart illustrating a process for producing beryllium-copper alloys according to the present invention. In this example, an alloy consisting of from 0.05 to 2.0% by weight of Be, from 0.1 to 10.0% by weight of at least one kind of Co and Ni, and optionally from 0.05 to 4.0% by weight of at least one kind of Si, Al, Mg, Zr, Sn, and Cr, and the balance being Cu and unavoidable impurities is cast, thereby obtaining a cast ingot. The thus obtained cast ingot is hot forged, and repeatedly cold rolled and annealed for refining, thereby obtaining a raw product. This primary product is then subjected to a solution treatment at a given temperature range from 800 to 1,000°C, and is cold worked to obtain a desired shape, which is subjected to an annealing treatment at a temperature in the range from 750 to 950°C and 20 to 200°C lower than the solution treating temperature, desirably for 1 to 5 minutes. Finally, the resulting product is subjected to an ordinary age hardening treatment, thereby obtaining a beryllium-copper alloy material. In the following, specific examples of the present invention will be explained. The invention of course is not limited to these Examples. They are merely given in illustration of the invention. Alloys having various compositions shown in Table 1 were cast, hot forged, and further repeatedly cold rolled and annealed, and were then each divided into three pieces. Then, one of the groups was subjected to the solution treatment at temperatures shown in Table 1 according to the process of the invention (Sample Nos. 1-9, and 101 to 110). Another group was subjected to a solution treatment at an ordinary solution treating temperatures shown in Table 1 according to a conventional process (Sample Nos. 10-18 and 111-120). The other group was treated, only the solution treatment being effected at the same temperatures in Examples according to the present invention (Sample Nos. 19-27 and 121-130). In each group, the solution treatment was effected for 5 minutes. The alloys of the invention (Nos. 1-9 and 101 to 110) were then annealed at temperatures shown in Table 1, and cold rolled at 30%. Thereafter, with respect to each of the samples, a value R/t as a safety bending factor was determined by dividing a minimum radius of curvature, "R", at which the sample could be bent at 90° in a direction orthogonal to a rolling direction without being cracked by a thickness "t" of the sample. With respect to the alloys of the invention (No. 1-9 and 101-110) and the conventionally solution treated materials (No. 10-18 and 111-120), tensile strength and fatigue strength (under a stress of 60 kg/mm²) after an ordinary age hardening treatment were measured. In addition, in order to examine influences of the annealing temperatures in the present invention, alloys (Nos. 28, 29, 131 and 132) were solution treated at a temperature inside the scope of the present invention and annealed at annealing temperatures outside the scope of the invention, and their properties were measured. Results are shown in Tables 1 and 2. In Table 1, the grain size of the matrix and a percentage of precipitated grains of size not more than 0.3 µm were visually determined based on an optical microscopic photograph at an equal magnification. In the Tables, "conventional alloys" means those produced by the conventional process. As is obvious from the results in Tables 1 and 2, the alloys according to the present invention (Nos. 1-9 and 101-110) which underwent the solution treatment at the temperature range from 800 to 1,000°C, cold working, the annealing in the temperature range from 750 to 950°C and at a temperature lower than the solution treating temperature, and then the age hardening have a smaller grain size of the matrix as compared with the conventional alloys and comparative alloys, the percentages of the precipitated grains of size not more than 0.3 µm being not less than 40% (Nos. 1-9) or not less than 50% (Nos. 101-110). As a result, it is seen that excellent tensile strength, formability, and fatigue resistance could be obtained. Figs. 2(a) through (b) are optical microscopic photographs showing metallic structures of the beryllium-copper alloys each consisting of Cu-0.4 Be-2.0 Ni produced according to the conventional process and the process of the invention, respectively. Figs. 2(c) and (d) are optical microscopic photographs of beryllium-copper alloys each consisting of Cu-0.2 Be-2.5 Ni-0.6 Si produced according to the conventional process and the process of the invention, respectively. As is obvious from Figs. 2(a) through (d), in the alloys according to the present invention, the grains of the matrix are finer and the precipitate composed of the intermetallic compounds are finely dispersed. As is obvious from the aforegoing description, according to the process for producing the beryllium-copper alloys in the present invention, the alloys composed of given compositions are solution treated at a temperature range from 800 to 1,000°C higher than the conventional range to solid-solve the large precipitated grains into the matrix, cold worked so that the precipitating nuclei may readily be formed, and annealed at a temperature in the range from 750 to 950°C and from 20 to 200°C lower than the solution treating temperature. Thereby, the alloys can be obtained, in which a part of a solute is precipitated so that the percentage of the precipitated grains having the grain size of not more than 0.3 µm is not less than 40% (when at least one kind of Si, Al, Mg, Zr, Sn or Cr is not included) or not less than 50% (when at least one kind of Si, Al, Mg, Zr, Sn and Cr is included) in a dispersed state. Consequently, the alloys obtained according to the process of the present invention can be beryllium-copper alloys which have improved tensile strength, formability, and fatigue strength and are highly useful as spring materials, electrical parts such as connectors, etc., which are required to have high conductivity and strength.

Claims: A process for producing a beryllium-copper alloy, which comprises the steps of obtaining by melting a cast ingot comprising from 0.05 to 2.0% by weight of Be, from 0.1 to 10.0% by weight of at least one of Co and Ni, and optionally from 0.05 to 4.0% by weight in total of at least one of Si, Al, Mg, Zr, Sn and Cr, the balance being Cu and unavoidable impurities, and subjecting the cast ingot to a solution treatment at a temperature in the range from 800 to 1,000°C, cold working, annealing at a temperature in the range from 750 to 950°C, and then an age hardening treatment, wherein the annealing temperature is 20 to 200°C lower than the solution treatment temperature. A process according to claim 1 wherein in the alloy obtained the percentage of precipitated grains having a grain size of not more than 0.3 µm is not less than 40% by weight. A process according to claim 1 wherein in the alloy obtained from 0.05 to 4.0% by weight in total of at least one of Si, Al, Mg, Zr, Sn and Cr is present and the percentage of precipitated grains having a grain size of not more than 0.3 µm is not less than 50% by weight. A process according to any one of claims 1 to 3 wherein the amount of Be is in the range from 0.1 to 0.7% by weight. A process according to any one of claims 1 to 4 wherein the amount of at least one of Co and Ni is in the range from 0.2 to 4.0% by weight.

Inventors: ISHIKAWA, SHUHEI, IWADACHI, TAKAHARU, MATSUI, YOSUKE
Applicants: NGK INSULATORS, LTD.
Application year: 1987
Main classification: C22F1
IPC codes: C22F1, C22C9