SHAPED BODY FORMED OF COPPER-BERYLLIUM ALLOY AND METHOD OF MANUFACTURING SAME

Abstract: In manufacturing shaped parts of various products, such as relays and connectors, of Cu-Be alloy material, the aim is improved formability to withstand severe working conditions. Known processes include a solution treatment of a rolled sheet of Cu-Be alloy material followed by a cold rolling with a relatively low reduction; this suffers from degradation of the formability of the material. Also, mill-hardened Cu-Be alloy material subjected to an age hardening is dis­ advantageous in that desired formability of the alloy cannot be achieved without sacrifice of strength. The invention enables the recovery of the formability of the material by subjecting a rolled sheet of the Cu-Be alloy containing 0.2-0.8 wt% Be and 0.3-4.0 wt% Ni and/or Co to a solution treatement and cold rolling of 20% reduction or more, followed by annealing at 250-550°C. A high post aging strength of the material shaped into the desired configuration is then achieved by subjecting the shaped material to aging at 350-500°C.

Description: The present invention relates to the manufacture of a shaped body which comprises Be-Cu alloy material. For manufacturing various products such as relays and connectors, Be-Cu alloy is widely used as an excellent raw material with high mechanical strength and electrical conductivity. In view of the recent increasing needs for products of small size, there is the demand for a Be-Cu alloy material having a sufficient formability to withstand severe working conditions. It has been a conventional practice to produce a rolled sheet of Be-Cu alloy to be worked into a shaped parts body with a predetermined configuration, by casting and hot rolling the raw material, subjecting the hot rolled material repeatedly to cold rolling and annealing, and then to a subsequent solution treatment followed by a further cold rolling. Moreover, the above-mentioned rolled sheet of Be-Cu alloy is worked into the desired configuration of a parts body in either one of the following modes. The first mode is to subject the rolled sheet of the Be-Cu alloy to a subsequent age hardening, and deliver the material to customers as a so-called mill hardened material. The material is then subjected to various work treatments, including bending into the desired configuration of a parts body in the factory of the customer. In many cases, the shaped parts body so obtained is incorporated into the products as it is. The second mode is to deliver to customers the rolled sheet of the Be-Cu alloy which is then subjected to various work treatments to achieve the desired configuration of a parts body in the factory of the customer, and subsequently to an age hardening in the factory of either the customer or the raw material supplier, to form a complete parts body with a desired strength. In both modes, the cold rolling to be effected after the solution treatment is a parameter dominantly influential on the characteristics of the material, and is intended to improve the product strength, to prevent the deformation of the material after the aging, and to promote the age precipitation. In effecting the cold rolling subsequently to the solution treatment, an excessively high reduction results in a degradation in 90° bending characteristic of the rolled sheet when bent about an axis that is in parallel with the rolling direction; hence, even when the rolled sheet is shaped into the configuration of a parts body prior to the age hardening, a sufficient freedom degree of the shaping cannot be achieved. Consequently, for a material exhibiting an outstanding tendency of work hardening, the cold rolling is usually carried out with the reduction of no greater than 60%. In other words, it has been considered necessary to increase the number of repetitions of the cold rolling and the annealing prior to the solution treatment, and this results in difficulties in lowering the manufacturing cost. On the other hand, for the material already subjected to the age hardening as a mill hardened material, the material with a higher post aging strength has a decreased elongation, an inferior formability and markedly degraded degree of freedom of bending. Thus, the preservation of the desired formability of Be-Cu alloy could be achieved only with the sacrifice of the fundamental feature of the alloy, i.e. its excellent high strength. The above prior art is exemplified by WO 80/01169 which describes a process in which a cold rolling following solution treatment is followed by two age-hardening steps at respectively 260-430°C and 480-650°C, prior to straightening and stress relieving. An object of the present invention is to improve the Be-Cu alloy material, with an originally degraded formability as a result of the cold rolling with the reduction of 20% or more, such that the material is capable of withstanding a bending with a smaller radius of curvature during the shaping into the desired configuration of a parts body, and to readily realize the maximum post aging strength of the Be-Cu alloy which has already been shaped into the desired configuration. According to the present invention, a solution treatment is carried out with respect to a rolled Be-Cu alloy sheet including 0.2 to 0.8 wt% Be, 0.3 to 4.0 wt% Ni and/or Co, the balance consisting of Cu and unavoidable impurities. This sheet is subjected to a cold rolling with a reduction of 20% or more, and the cold rolled sheet is subjected to an annealing at a temperature of 250 to 550°C to release part of the work strain to recover the formability of the Be-Cu alloy material. The so-obtained material is subjected to necessary work, including bending into a predetermined configuration of the parts body, and then to an aging at a temperature of 350-500°C, thereby to realize the maximum post aging strength. There is shown in the sole Figure a flow chart of the production steps wherein the present invention is compared with the above-mentioned prior art. Conventionally, either the cold rolled sheet obtained after the solution treatment of the Be-Cu alloy is directly subjected to shaping into the desired configuration and to a subsequent age hardening, or the mill hardened material obtained after the advance age hardening is subjected to shaping into the configuration of the product. As mentioned hereinbefore, such production steps accompany a variety of problems. In contrast to the above, according to the present invention, the cold rolling carried out after the solution treatment is followed by an annealing at a predetermined temperature thereby to release part of the work strain and to recover the formability, and the so-obtained Be-Cu alloy material with an improved formability is then shaped into the desired configuration of the final body and subjected to an age hardening, whereby it becomes possible to produce products with a desired high strength. According to the present invention, as mentioned hereinbefore, use is made of Be-Cu alloy which includes 0.2 to 0.8 wt% Be, 0.3 to 4.0 wt% Ni and/or Co, the balance consisting of Cu and unavoidable impurities. These limitations on each of the components are based on the following reasons. First of all, it has been found that with the amount of Be of less than 0.2 wt% a sufficient precipitation hardening cannot be achieved, while when the amount of Be exceeds 0.8 wt% an improvement in the strength in conformity with the increased amount cannot be recognized; hence, the amount of Be has been defined as ranging from 0.2 to 0.8 wt%. Secondly, it has also been found that with the amount of Ni and/or Co of less than 0.3 wt% a sufficient precipitation hardening cannot be achieved, while when the amount of Ni and/or Co exceeds 4.0 wt% the formability degrades; hence, the amount of Ni and/or Co has been defined as ranging from 0.3 to 4.0 wt%. According to the present invention, the rolled sheet of Be-Cu alloy with the above-mentioned composition is subjected to a cold rolling, following the solution treatment, with the reduction of 20% or more. This is due to recognition that, with a reduction of less than 20%, the formability does not undergo a significant degradation and does not require the recovery by the annealing, while a higher reduction makes it possible to reduce the number of repetition of the cold rolling and annealing in advance of the solution treatment. Moreover, for effecting the annealing between the cold rolling step following the solution treatment and the working step for shaping the material into the desired configuration of the parts body, the present invention defines the temperature range of 250 to 550°C due to the reason that the temperature below 250°C does not result in a sufficient recovery of the formability, on one hand, while the temperature above 550°C results in an excessively aged state whereby a sufficiently high strength cannot be achieved through the age hardening after the shaping into the desired configuration, on the other hand. Furthermore, for effecting age hardening following the shaping into the desired parts body configuration, the present invention defines the temperature range of 350 to 500°C due to the reason that the temperature below 350°C does not induce the precipitation hardening, on one hand, and the temperature above 500°C, though effective to improve the electrical conductivity, results in an excessively aged state whereby a sufficient strength cannot be achieved, on the other hand. EXAMPLES There is shown, in the following Table 1, the compositions, production conditions and mechanical properties of samples (1) to (16) of the present invention and comparative samples (17) to (24). The samples (1) to (24) listed in Table 1 have been produced in a known manner up to the solution treatment step in the process shown in the Figure, and subsequently under respectively different process conditions. The formability as mentioned in Table 1 and claim 2 hereof has been determined with respect to rolled sheets of Be-Cu alloy prior to the age hardening step, and is expressed as R/t value, where R is a safety bending radius determined by whether or not cracks are formed in the bent portion of the sheet after it has been bent by 180° about an axis in parallel with the rolling direction, and t is the thickness of the sheet by which the safety bending radius is divided. Here, a smaller R/t value indicates that the sheet is capable of withstanding a more severe work conditions including bending with a smaller bending radius. As Table 1 clearly shows, all the samples (1) to (16) of the present invention exhibit excellent formability and strength (post aging 0.2% yield strength obtained in accordance with JIS Z2241). On the other hand, the comparative samples (17), (19) and (21) are of the same composition as the samples (5) to (8) of the present invention, while the comparative samples (18), (20) and (22) are of the same composition as the samples (10) and (11) of the present invention. With respect to the comparative samples (17) and (18), the cold rolling has been carried out with a smaller reduction. It is apparent that, with the reduction of 15%, an excellent formability can be achieved though the post aging 0.2% yield strength becomes much lower as compared with the corresponding samples of the present invention having the same composition. With respect to the comparative sample (19), the annealing has been carried out at a higher temperature so that the precipitation nuclei became coarse accompanying decrease in the post aging 0.2% yield strength. As to the comparative sample (20), the annealing has been carried out under a lower temperature so that is was not possible to achieve a sufficient recovery of the formability after the annealing. The comparative sample (21) exhibits an excessively aged state as a result of aging under a higher temperature, while the comparative sample (22) is in a non-aged state due to the aging treatment under a lower temperature; for both of these samples the post aging 0.2% yield strength has decreased. Furthermore, a sufficient strength could not be achieved for the comparative samples (23) and (24) due to insufficient content of Be or Co, respectively. Another samples have been prepared to have the same composition as the samples (10) and (11) of the present invention, and these samples were subjected to cold rolling with the variable reduction of 20 to 90%, to a subsequent annealing at the temperature of 400°C followed by the measurement of the formability, and then to an aging at the temperature of 400°C followed by the measurement of the 0.2% yield strength. The result is as shown in the following Table 2. As is apparent from Table 2, a higher reduction of the cold rolling results in a degradation of the formability which, in accordance with the present invention, can be recovered to a practically high R/t value by effecting the annealing. It will be appreciated that, in accordance with the present invention, the cold rolling following the solution treatment is carried out with a higher value such as to improve the post aging strength and to prevent post aging deformations in an effective manner. Also, the degradation of the formability, which has hitherto been considered inevitable, can be prevented positively by the annealing at a predetermined temperature. Furthermore, with the higher reduction of the cold rolling following the solution treatment, the solution treatment can be carried out with respect to the sheet of a greater thickness. As an example, in case of the reduction of 80% and the final product thickness of 0.2 mm, the solution treatment can be effected with respect to the sheet of 1.0 mm thickness. Hence, it is possible to reduce the number of repetition of the cold rolling and the annealing in advance of the solution treatment, as compared with the cold rolling in the conventional process with a lower reduction, and to thereby achieve a substantial economical advantage. Moreover, when the annealing is effected with respect to a constrained sheet, the shape of the sheet can be properly corrected and also the aging precipitation can be more or less prompted, so that it is possible to prevent undesirable shrinkage arising during the aging after the material has been worked into the configuration of the parts body.

Claims: A method of manufacturing a shaped body comprising a Be-Cu alloy material with a predetermined configuration, the method comprising subjecting a rolled sheet of Be-Cu alloy which includes 0.2 to 0.8 wt% Be, 0.3 to 4.0 wt% Ni and/or Co, the balance consisting of Cu and unavoidable impurities, to the following treatment steps: A. subjecting said rolled sheet to a solution treatment; B. cold rolling said rolled sheet with a reduction of 20% or more; C. subjecting the cold rolled sheet to annealing at a temperature of 250 to 550°C to release part of the work strain and to recover the formability to form a Be-Cu alloy raw material; D. working, including bending, the so-obtained alloy raw material, in its annealed state and prior to any age-hardening, into a predetermined final body configuration; and E. aging the worked alloy material at a temperature of 350 to 500°C. A method according to claim 1 wherein said annealing step C is performed so that the sheet achieves a formability (as herein defined) R/t≦5 where R is the bending radius and t is the thickness of the rolled sheet of Be-Cu alloy in the formability test.

Inventors: MATSUI, YOSUKE
Applicants: NGK INSULATORS, LTD.
Application year: 1988
Main classification: C22F1
IPC codes: C22C9, C22F1