A lead-free, free-machining, and easily machinable beryllium copper alloy and its preparation method

Abstract

This invention discloses a lead-free, free-machining beryllium copper alloy and its preparation method, relating to the field of metal alloy material preparation technology. The method includes: preparing beryllium copper matrix units free of intentionally added tellurium and lead elements; determining the tellurium loading per unit area according to the target tellurium content of the finished product, and setting discontinuously patterned tellurium-containing reactive micro-interlayers between adjacent beryllium copper matrix units; sequentially performing restricted reaction pretreatment, hot-pressing-shear composite densification, interface stabilization treatment, plastic working, cold working, and aging treatment to obtain a lead-free, free-machining beryllium copper alloy with a tellurium content of 0.0030% to 0.0100%. The resulting alloy comprises a continuous copper matrix and discrete tellurium-rich sections. The discrete tellurium-rich sections do not form a continuous tellurium-rich network along the original interface direction, thus balancing chip-breaking performance and mechanical load-bearing capacity.

Description

Technical Field

[0001] This invention relates to the field of metal alloy material preparation technology, and in particular to a lead-free, easy-to-cut and easy-to-process beryllium copper alloy and its preparation method. Background Technology

[0002] Beryllium copper alloys possess strength, elastic recovery, and electrical conductivity, making them commonly used in precision electronic connectors, elastic components, and highly reliable mechanical parts. To improve the machinability of beryllium copper alloys, related technologies introduce cutting-promoting components such as tellurium, sulfur, and lead. However, lead is becoming increasingly unsuitable for continued use due to environmental protection and electronic material restrictions. Therefore, it is necessary to improve the chip-breaking performance of beryllium copper alloys under lead-free conditions.

[0003] When introducing tellurium-based cutting-promoting components under lead-free conditions, if tellurium is added via a monolithic melt or a continuous interface, the tellurium-rich phase easily forms continuous brittle channels along grain boundaries or the original interface direction. This couples the cutting fracture path with the load-bearing path, resulting in improved chip-breaking performance but decreased load-bearing continuity. Therefore, a preparation method is needed that can confine the tellurium-containing component within a local reaction domain and transform it into discrete tellurium-rich segments during subsequent processing. This allows the tellurium-rich segments to trigger local cutting fracture, while the continuous copper matrix maintains load-bearing continuity. Summary of the Invention

[0004] In view of this, this application provides a lead-free, easy-to-cut, and easy-to-machinate beryllium copper alloy and a method for preparing the same.

[0005] According to one aspect of this disclosure, a lead-free, free-machining, and easily machinable beryllium copper alloy is provided, comprising 0.20%–2.00% beryllium, 0.0030%–0.0100% tellurium, 0.10%–0.30% zinc, 0.05%–0.60% total cobalt and nickel, ≤0.15% iron, ≤0.15% aluminum, ≤0.10% silicon, with the balance being copper and unavoidable impurities, wherein the lead content is not greater than 0.005%.

[0006] According to another aspect of this disclosure, a method for preparing a lead-free, easy-to-cut, and easy-to-process beryllium copper alloy is also provided, comprising: preparing beryllium copper matrix units free of intentionally added tellurium and lead elements; determining the tellurium loading per unit area according to the target tellurium content of the finished product, and setting discontinuously patterned tellurium-containing reactive micro-interlayers between adjacent beryllium copper matrix units; performing a restricted reaction pretreatment on the assembled billet to form a local initial reaction zone between the local reaction domain and the adjacent copper matrix region; and performing hot pressing-shearing on the assembled billet after the restricted reaction pretreatment. The composite densification process transforms the initial reaction zone into a tellurium-containing reaction connection zone, which is then thinned, separated, and discretized. An interface stabilization treatment is then applied to the newly formed interface billet to maintain a continuous distribution of the new copper-based contact area between adjacent dispersed tellurium-rich sections and reduce residual porosity, resulting in a continuous copper-based contact composite billet. Finally, the continuous copper-based contact composite billet undergoes plastic forming, cold working, and aging treatments to obtain a lead-free, free-machining, and easily machinable beryllium copper alloy with discrete tellurium-rich sections distributed within a continuous copper matrix.

[0007] The beneficial effects of this invention are as follows: by using discontinuously patterned tellurium-containing reactive micro-layers, the tellurium-containing components are confined within the local reaction domain, so that the tellurium-containing region is transformed into discrete tellurium-rich segments after the confined reaction and thermo-pressing-shear composite action, thus avoiding the formation of a continuous through network of tellurium-rich structures along the original interface direction; the newly formed copper-based contact areas between adjacent discrete tellurium-rich segments are kept continuously distributed after interface stabilization treatment, so that the continuous copper matrix bears the overall load-bearing role, and the discrete tellurium-rich segments bear the local fracture triggering role during the cutting process, thereby taking into account both chip breaking performance and mechanical load-bearing performance under lead-free conditions. Attached Figure Description

[0008] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0009] Figure 1 Flowchart of the preparation method for lead-free, easy-to-cut, and easy-to-machine beryllium copper alloy.

[0010] Figure 2 This is a schematic diagram of a discontinuously patterned tellurium-containing reactive micro-sandwich structure.

[0011] Figure 3 This is a schematic diagram of the organizational evolution of tellurium-containing regions.

[0012] Figure 4 This is a schematic diagram for calculating the tellurium load per unit area.

[0013] Figure 5 This is a schematic diagram of SEM / EDS detection after restricted reaction pretreatment.

[0014] Figure 6 This is a schematic diagram of SEM / EDS detection of a hot-pressed-shear interrupted sample.

[0015] Figure 7 This is a schematic diagram of SEM / EDS testing of the hot-pressed-sheared sample.

[0016] Figure 8 This is a schematic diagram of SEM / EDS detection after interface stabilization processing.

[0017] Figure 9 This is a comparison diagram of the present invention and a tellurium-rich network as a comparative example of a continuous, full-surface tellurium-containing layer.

[0018] Figure 10 This is a schematic diagram of the cross-section or fracture surface morphology of the chip. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0020] This invention relates to a lead-free, easy-to-cut, and easy-to-process beryllium copper alloy and its preparation method. By setting discontinuously patterned tellurium-containing reactive micro-interlayers between adjacent beryllium copper matrix units, the tellurium-containing components are confined to multiple spaced local reaction domains before the confined reaction pretreatment. After confined reaction pretreatment, hot pressing-shear composite densification, interface stabilization treatment, and subsequent plastic processing, cold working, and aging treatment, the tellurium-containing regions are transformed into discrete tellurium-rich segments distributed in a continuous copper matrix, thereby avoiding the formation of a continuous tellurium-rich network along the original interface direction.

[0021] Reference Figure 1 The method for preparing the lead-free, free-machining, and easily machinable beryllium copper alloy of the present invention includes the preparation of beryllium copper matrix units, the setting of discontinuous patterned tellurium-containing reactive micro-layers, confined reaction pretreatment, hot pressing-shear composite densification, interface stabilization treatment, and plastic processing, cold working, and aging treatment. Through the above steps, the tellurium-containing component is not distributed in a way that is added as a whole melt or continuously in a full-surface interlayer, but rather forms multiple spaced local reaction domains between adjacent beryllium copper matrix units, which are then transformed into dispersed tellurium-rich segments in a continuous copper matrix during subsequent processing. The lead-free, free-machining beryllium copper alloy comprises, by mass percentage: 0.20%–2.00% beryllium, 0.0030%–0.0100% tellurium, 0.10%–0.30% zinc, 0.05%–0.60% total cobalt and nickel, ≤0.15% iron, ≤0.15% aluminum, and ≤0.10% silicon, with the balance being copper and unavoidable impurities, wherein the lead content is not greater than 0.005%. The lead-free, free-machining beryllium copper alloy comprises a continuous copper matrix and discrete tellurium-rich segments distributed within the continuous copper matrix. The Te content in the discrete tellurium-rich segments is higher than the Te content in the adjacent continuous copper matrix. The discrete tellurium-rich segments exhibit at least one of the following morphologies: short strips, islands, and granules, and do not form a continuous tellurium-rich network along the original interface direction.

[0022] The pre-assembled state refers to the state in which, before the restricted reaction pretreatment is performed, the beryllium copper substrate units, copper foil carrier, and discontinuously patterned tellurium-containing reactive micro-layers have formed an assembled blank according to a predetermined stacking sequence. In this state, the tellurium-containing reactive micro-layers are located between adjacent beryllium copper substrate units, local reaction domains are distributed at preset pattern intervals, and copper-based spacers are retained between adjacent local reaction domains. The original interface direction refers to the initial extension direction of the contact surface between adjacent beryllium copper substrate units in the assembled blank; after subsequent processing, the original interface direction is determined by the initial setting position of the tellurium-containing reactive micro-layers, the concentrated distribution zone of tellurium-rich sections, and the sample sampling direction.

[0023] The continuous copper matrix refers to a copper-based region that is continuously distributed across the original interface region within the statistical field of view and is not interrupted by continuous pores or a tellurium-rich network extending along the original interface direction. The discrete tellurium-rich segment refers to a tellurium-rich region with a Te content higher than that of the adjacent continuous copper matrix and divided into two or more unconnected segments by the continuous copper matrix. The continuous copper-based region refers to a copper-based region located between adjacent tellurium-rich regions, characterized primarily by a continuous distribution of Cu and not interrupted by continuous pores. The continuously connected tellurium-rich network refers to a tellurium-rich distribution where the Te-rich regions are continuously connected along the original interface direction and extend through the statistical field of view, or maintain continuous connection between adjacent statistical fields of view. When the Te-rich regions are divided into multiple unconnected segments by the continuous copper matrix, and no continuous Te enrichment band extending through the statistical field of view is observed in at least three original interface regions, the discrete tellurium-rich segment is considered not to form a continuously connected tellurium-rich network extending along the original interface direction.

[0024] The total tellurium content in the final product is determined by the tellurium loading per unit area of ​​the tellurium-containing reactive microlayer, the area ratio of local reaction domains, the thickness of the beryllium copper matrix unit, the number of interfaces, and the tellurium retention state after subsequent processing, rather than being directly determined by the local mass fraction of tellurium-containing material within the local reaction domain. The tellurium loading per unit area refers to the mass of tellurium introduced by the discontinuously patterned tellurium-containing reactive microlayer within a unit projected area. Specifically, the total mass of the beryllium copper matrix unit, copper foil carrier, and tellurium-containing reactive microlayer within a unit area is first determined. Then, the tellurium loading per unit area is determined according to the target tellurium content of the finished product. After the finished product is obtained, inductively coupled plasma atomic emission spectrometry (ICP-AES) is used to detect the tellurium content in the finished product sample, and the detected value confirms that the overall tellurium content of the finished product is within the range of 0.0030% to 0.0100%.

[0025] When converting tellurium loading per unit area to the finished product tellurium content, the total mass per unit area is the sum of the dry weights of all beryllium copper substrate units, copper foil carriers, and tellurium-containing dry films within the unit projected area. The mass of tellurium introduced per unit area is multiplied by the tellurium retention ratio after subsequent processing to obtain the tellurium retention mass per unit area. The ratio of the tellurium retention mass per unit area to the total mass per unit area is taken as the theoretical finished product tellurium content. After plastic processing, cold working, and aging treatment, the measured values ​​of inductively coupled plasma atomic emission spectrometry are used as the final verification result. When the measured tellurium content is lower than the target range, the tellurium loading per unit area or the proportion of the local reaction domain area is increased; when the measured tellurium content is higher than the target range, the tellurium loading per unit area or the proportion of the local reaction domain area is decreased.

[0026] Reference Figure 4 The tellurium loading per unit area is determined by the unit projected area, the mass difference before and after local loading, and the tellurium mass fraction in the tellurium-containing dry film. Specifically, within a unit projected area A0, the mass m0 of the copper foil carrier before local loading is first obtained, and then the mass m1 after local loading with the tellurium-containing dry film is obtained. The difference dm is the tellurium-containing dry film increment. The tellurium-containing dry film increment dm is multiplied by the tellurium mass fraction wTe in the tellurium-containing dry film, and then divided by the unit projected area A0 to obtain the tellurium loading per unit area. In this way, the tellurium mass introduced by the tellurium-containing reactive microlayer corresponds to the tellurium content of the target finished product, and can be verified by inductively coupled plasma atomic emission spectrometry after the finished product is prepared.

[0027] The tellurium-containing reactive microlayer is formed by locally loading a tellurium-containing dry film onto the surface of a copper foil carrier. The thickness of the copper foil carrier is 10 micrometers to 40 micrometers, the area ratio of the local reactive domain is 20% to 40%, and the tellurium loading per unit area of ​​the tellurium-containing reactive microlayer is 0.06 mg / cm² to 0.20 mg / cm². The tellurium content of the final lead-free, free-machining, and easily machinable beryllium copper alloy, as measured by inductively coupled plasma atomic emission spectrometry, is 0.0030% to 0.0100%. The tellurium-containing dry film is formed by a tellurium source, copper-based auxiliary components, and a volatile carrier, and is locally deposited on the surface of the copper foil carrier and dried. The tellurium loading per unit area is calculated by considering the mass change of the copper foil carrier before and after local loading, the area ratio of the local reactive domain, and the mass fraction of tellurium in the tellurium-containing dry film, and is verified by the chemical composition test results of the finished product.

[0028] In specific implementation, the tellurium source is any one of tellurium powder, copper-tellurium composite powder, or tellurium-containing copper-based composite powder; the copper-based auxiliary component is copper powder; and the volatile carrier is ethanol, terpineol, or a volatile slurry system containing an organic binder. After mixing the tellurium source, copper-based auxiliary component, and volatile carrier to form a tellurium-containing slurry that can be locally loaded, it is applied to a predetermined local reaction domain on the surface of a copper foil carrier by means of stencil printing, screen printing, or dispensing. Then, it is dried at 60°C to 120°C until the quality is stable to form a tellurium-containing dry film.

[0029] The local reaction domains can be either island-shaped or segmented patterns. When the local reaction domains are island-shaped, the equivalent diameter of the island-shaped pattern is 60 micrometers to 160 micrometers, and the center-to-center spacing is 90 micrometers to 220 micrometers. When the local reaction domains are segmented, the length of the segmented pattern is 120 micrometers to 240 micrometers, the width is 20 micrometers to 60 micrometers, the segment spacing is 80 micrometers to 160 micrometers, and the long axis of the segmented pattern is arranged along the shear direction. The discontinuous patterned structure allows the tellurium-containing component to be distributed in the form of local reaction domains between adjacent beryllium copper matrix units, while retaining copper matrix spacer regions between adjacent local reaction domains, so that subsequent tellurium-containing regions do not react and extend along the original interface direction in the form of a continuous layer.

[0030] Reference Figure 2 Intermittently patterned tellurium-containing reactive micro-layers are disposed between adjacent beryllium copper substrate units. The tellurium-containing reactive micro-layers can be formed by locally loading tellurium-containing dry films on the surface of copper foil carriers. Figure 2The local reaction domains can be island-shaped or segmented. When using an island-shaped pattern, the central spacing between each island-shaped local reaction domain is maintained, allowing the tellurium-containing components to be distributed at intervals along the interface direction. When using a segmented pattern, the long axis of the segmented local reaction domains is arranged along the shear direction, making them easier to thin, neck, and separate during subsequent hot-pressing-shear composite densification. A copper foil carrier and copper-based spacer are retained between adjacent local reaction domains, providing initial space for the subsequent formation of a continuous copper-based region.

[0031] Reference Figure 3 The microstructure evolution of the tellurium-containing region sequentially includes a pre-assembled state, a confined reaction pretreatment state, a thermo-pressing-shear composite densification state, and a state after interface stabilization treatment. In the pre-assembled state, the tellurium-containing component is located in the original interface direction as a local reaction domain. After the confined reaction pretreatment, a local initial reaction zone is formed between the local reaction domain and the adjacent copper-based region. During the thermo-pressing-shear composite densification process, the local initial reaction zone is transformed into a tellurium-containing reaction connection region, and undergoes thinning, necking, separation, and discretization under the combined action of compression and shear. After interface stabilization treatment and subsequent processing, the tellurium-containing region is transformed into a dispersed tellurium-rich segment distributed in a continuous copper matrix, and a continuous copper-based region is formed between adjacent dispersed tellurium-rich segments.

[0032] The preparation method of the lead-free, free-cutting, and easily machinable beryllium copper alloy of the present invention includes the following steps.

[0033] First, a beryllium copper matrix unit free of intentionally added tellurium and lead is prepared. The beryllium copper matrix unit is made of beryllium copper strip, which, by mass percentage, comprises 0.20%–2.00% beryllium, 0.10%–0.30% zinc, 0.05%–0.60% total cobalt and nickel, ≤0.15% iron, ≤0.15% aluminum, and ≤0.10% silicon, with the balance being copper and unavoidable impurities. The lead content in the beryllium copper strip is no greater than 0.005%, and the tellurium content is no greater than 0.002%. In practice, the beryllium copper strip is obtained from the same batch of base material, and after smelting, homogenization, hot rolling, and cold rolling, it is made into a beryllium copper strip with a thickness of 0.80 mm–1.50 mm; in one specific embodiment, the thickness of the beryllium copper strip is 1.20 ± 0.02 mm.

[0034] Secondly, the tellurium loading per unit area of ​​the tellurium-containing reactive micro-layer is determined according to the target tellurium content of the finished product. Discontinuously patterned tellurium-containing reactive micro-layers are then formed between adjacent beryllium copper substrate units to create an assembled blank. The tellurium-containing reactive micro-layer consists of multiple spaced local reaction domains, with copper-based spacers remaining between them. These copper-based spacers provide initial space for the subsequent formation of continuous copper-based regions between adjacent tellurium-rich segments.

[0035] Next, a confined reaction pretreatment is performed on the assembled preform containing the tellurium-containing reactive micro-layer. This confined reaction pretreatment refers to the process prior to hot-pressing-shear composite densification, where the tellurium-containing components, under the constraint of a discontinuous patterned spatial distribution, primarily react locally within a local reaction domain and its adjacent copper-based region. The confined reaction pretreatment is carried out under a protective atmosphere at a temperature of 540°C–590°C for a holding time of 5–30 minutes. This process creates a local initial reaction zone between the local reaction domain and the adjacent copper-based region, preventing the formation of a continuous, all-encompassing reaction layer along the original interface direction. The local initial reaction zone is confirmed by cross-sectional scanning electron microscopy and energy dispersive spectroscopy (EDS) elemental distribution detection.

[0036] The local initial reaction zone and tellurium-containing reaction connection zone do not require the identification of a specific copper telluride phase as a necessary condition. Instead, the identification criteria are the changes in cross-sectional morphology, the enrichment location of Te element, the continuous distribution relationship of Cu element, and the contact state between the tellurium-rich region and the adjacent copper-based region. When the phase composition is not verified, only the region with a Te element content higher than that of the adjacent continuous copper matrix is ​​described as a tellurium-rich section, without limiting it to a specific copper telluride phase.

[0037] Reference Figure 5 After the restricted reaction pretreatment, local initial reaction bands are formed between the local reaction domains and adjacent copper-based regions. In the SEM / BSE observation area, the local initial reaction bands are located near the original interface direction and are distributed around the local reaction domains; in the Te element EDS detection area, the Te enrichment signal is mainly concentrated at the corresponding positions of each local reaction domain, and a continuous, unbroken reaction layer is not formed along the original interface direction. This state indicates that the restricted reaction pretreatment causes local reactions of the tellurium-containing components, but still maintains a discontinuous distribution characteristic.

[0038] Then, the assembled green body pretreated with restricted reaction is subjected to hot-pressing-shear composite densification, which transforms the local initial reaction zone into a tellurium-containing reaction connection zone. This tellurium-containing reaction connection zone is then thinned, separated, and discretized under the combined action of compression and shearing, resulting in a new interface green body with dispersed tellurium-rich sections. The hot-pressing-shear composite densification is carried out at 700°C–760°C and 15 MPa–35 MPa, with a holding time of 5–15 minutes, using either a unidirectional shear path or a cross-shear path. When using a unidirectional shear path, a unidirectional shear displacement of 0.5 mm–2.5 mm is applied; when using a cross-shear path, a first-direction shear displacement of 0.5 mm–1.5 mm and a second-direction shear displacement of 0.4 mm–1.2 mm are applied sequentially.

[0039] Reference Figure 6Under the interrupted state of hot-pressing-shear composite densification, the tellurium-containing reaction-connected region extends along the shear direction under the combined action of compressive load and shear displacement, exhibiting thinning and necking. In the corresponding Te element EDS detection region, the Te enrichment signal extends along the shear direction, but there are still local interruptions between adjacent Te-rich regions, indicating that the tellurium-containing reaction-connected region has transformed from an initial local reaction zone to a dispersed tellurium-rich segment, but has not yet been completely segmented.

[0040] The initial local reaction zone transforms into a tellurium-containing reaction-connected region under hot pressing. This region undergoes morphological elongation and cross-sectional thinning along the shear direction under shearing, and is further divided into multiple dispersed tellurium-rich segments by the separation effect of adjacent copper-based continuous regions. The formation of a tellurium-containing reaction-connected region is not determined by the formation of a complete metallurgical diffusion bond, nor by the generation of continuous cracks; rather, it is confirmed through cross-sectional scanning electron microscopy and energy dispersive spectroscopy (EDS) elemental distribution detection. When the tellurium-rich region corresponding to the same local reaction domain is divided into two or more non-connected segments by a copper-based continuous region, and the width of the copper-based continuous region between adjacent tellurium-rich regions is not less than 2 micrometers, the tellurium-containing reaction-connected region is considered to have formed a separated state. When the maximum continuous tellurium-rich length in the original interface direction of the tellurium-rich region within the statistical region is lower than the corresponding value after restricted reaction pretreatment, the tellurium-containing reaction-connected region is considered to have formed a discretized state. The statistical region is set along the original interface direction, and no fewer than three observation fields are selected for each sample.

[0041] Reference Figure 7 After hot-pressing-shear densification, the tellurium-containing reactive zone was divided into multiple unconnected, dispersed tellurium-rich segments by a copper-based continuous zone. In the SEM / BSE observation area, copper-based continuous zones existed between adjacent dispersed tellurium-rich segments, and these continuous zones formed a connection along the original interface direction. In the Te element EDS detection area, the Te enrichment signal was distributed in short segments, islands, or granular intervals, no longer forming continuous banded enrichment. This state indicates that hot-pressing-shear densification reduced the average continuous length of the tellurium-rich region and the maximum continuous tellurium-rich length along the original interface direction.

[0042] Subsequently, an interface stabilization treatment is performed on the newly formed interface blank to maintain the continuous distribution of the newly formed copper-based contact area between adjacent dispersed tellurium-rich sections and reduce residual porosity at the shear separation boundary, resulting in a copper-based continuous contact composite blank. The interface stabilization treatment is carried out at 680°C–730°C and 5 MPa–15 MPa for 10–60 minutes. The interface stabilization treatment targets the newly formed copper-based contact area formed after hot-pressing-shear composite densification and the residual porosity at the shear separation boundary; this treatment is not a secondary diffusion welding of the undensified integral blank, nor is the formation of a continuous diffusion weld interface on the entire surface used as a criterion. The reduction in residual porosity refers to a decrease in the porosity area fraction at the shear separation boundary compared to a control sample of the same process without interface stabilization treatment; the copper-based continuous contact composite blank does not require the original interface area to be completely pore-free, nor does it mean that all residual micropores are completely eliminated.

[0043] Reference Figure 8 After interface stabilization treatment, the continuity of the newly formed copper-based contact area between adjacent dispersed tellurium-rich sections improved, and the residual micropores at the shear separation boundary decreased. In the SEM / BSE observation area, the dispersed tellurium-rich sections remained intermittently distributed, and adjacent tellurium-rich sections were connected by continuous contact areas of the newly formed copper-based matrix; in the Te element EDS detection area, the Te enrichment signal still showed a discontinuous distribution. This state indicates that the interface stabilization treatment did not form a continuous, whole-surface tellurium-rich reaction layer, but rather improved the continuous bearing capacity of the copper-based matrix while maintaining the discretization of the tellurium-rich sections.

[0044] Finally, the copper-based continuous contact composite billet is subjected to plastic processing, cold working, and aging treatment to obtain a lead-free, free-machining, and easily machinable beryllium copper alloy. The plastic processing includes hot extrusion and drawing. The hot extrusion temperature is 720°C–760°C, and the extrusion ratio is 6:1–14:1. The cumulative deformation amount of the cold working is 20%–45%. The aging treatment includes a first-stage aging and a second-stage aging. The first-stage aging temperature is 280°C–340°C, and the second-stage aging temperature is 360°C–430°C. The plastic processing, cold working, and aging treatment are used to ensure that the continuous copper matrix obtains a stable load-bearing structure while maintaining the dispersion of discrete tellurium-rich regions within the continuous copper matrix.

[0045] To confirm the above preparation process and the microstructure of the obtained product, the present invention performs component closure detection, cross-sectional microstructure detection, elemental distribution detection, continuous length statistics of tellurium-rich sections, pore area fraction statistics of the original interface region or corresponding sampling region, copper-based continuous contact state composite determination, mechanical property detection, and cutting chip breaking performance detection on the samples obtained from the examples and comparative examples with original interface regions or corresponding sampling regions. For comparative examples with overall tellurium addition and no tellurium-containing reaction micro-interlayer original interface, the maximum continuous tellurium-rich length and pore area fraction in the original interface direction are not included as statistical items of the original interface region. The component closure detection is used to confirm the correspondence between the tellurium loading per unit area and the total tellurium content of the finished product. The cross-sectional microstructure detection and elemental distribution detection are used to confirm the formation state of the local initial reaction zone, the tellurium-containing reaction connection zone, the dispersed tellurium-rich section, and the copper-based continuous region. The continuous length statistics of the tellurium-rich section are used to confirm whether the tellurium-rich region forms a continuous tellurium-rich network along the original interface direction. The composite determination of the pore area fraction and the continuous contact state of the copper-based layer is used to confirm the continuous load-bearing state of the copper-based layer between adjacent tellurium-rich sections. The mechanical property detection and cutting chip breaking performance detection are used to evaluate the load-bearing performance and machinability of the obtained beryllium copper alloy.

[0046] In the compositional closure test, the thickness, area, mass, and local reaction domain area ratio of the beryllium copper substrate unit, copper foil carrier, and tellurium-containing dry film were recorded respectively. The mass of tellurium introduced by the tellurium-containing reaction micro-layer was calculated according to the unit projected area to obtain the tellurium loading per unit area. For the finished samples after plastic processing, cold working, and aging treatment, the test sample was cut from the middle of the sample, the surface oxide layer and processing contamination layer were removed, and then the sample was cleaned and dried. The chemical composition was then detected by inductively coupled plasma atomic emission spectrometry. At least three parallel samples were set for each sample, and the contents of at least Be, Te, Zn, Co, Ni, Fe, Al, Si, and Pb were tested. The measured value of Te was used to confirm that the overall tellurium content of the finished product was between 0.0030% and 0.0100%, and the measured value of Pb was used to confirm that the detected value of lead was not greater than 0.005%.

[0047] In cross-sectional microstructure detection, samples were taken from the original interface region and its adjacent regions after confined reaction pretreatment, hot-pressing-shear composite densification, interface stabilization treatment, and the final product state. For comparative examples without tellurium-containing reaction micro-interlayers at the original interface, samples were taken from the region corresponding to the same sampling direction and processing position as in the examples. After mounting, grinding, and polishing, the cut samples were prepared into cross-sectional observation samples and observed using a scanning electron microscope. Scanning electron microscopy was performed using backscattered electron imaging, with an observation voltage of 10 kV to 20 kV and a working distance of 8 mm to 12 mm. Each sample was selected with no less than three independent observation fields, with magnifications of 500x, 2000x, and 5000x. The 500x field of view was used to observe the overall continuous state of the original interface region or the corresponding sampling region; the 2000x field of view was used to statistically analyze the continuous length and porosity distribution of the tellurium-rich region; and the 5000x field of view was used to observe the local morphology of the copper-based continuous region and the shear separation boundary between adjacent tellurium-rich sections.

[0048] In elemental distribution detection, energy dispersive spectroscopy (EDS) surface and line scans are performed within the same cross-sectional area observed by scanning electron microscopy (SEM). At least the distribution of Cu and Te elements is detected, and the distribution of other alloying elements is detected if necessary. The EDS scanning voltage is 10 kV–20 kV, and the acquisition time for a single field of view is 60–120 seconds. Tellurium-rich regions are identified by the location of Te enrichment, and the existence of a continuous copper-based region between adjacent tellurium-rich regions is confirmed by the continuous distribution of Cu. It is also observed whether the Te enrichment region forms a continuous, interconnected distribution along the original interface direction. EDS point analysis or surface averaging analysis is performed on discrete tellurium-rich sections and their adjacent continuous copper matrix. When the Te signal intensity or Te content in the detected region of the tellurium-rich section is higher than that in the adjacent continuous copper matrix region, that region is identified as a Te enrichment region.

[0049] In the continuous length statistics of tellurium-rich sections, no fewer than three independent observation fields are selected in the original interface region or corresponding sampling region of each sample, and the sampling direction, magnification and statistical width of each sample are kept consistent. The Te enrichment region is calibrated according to the energy spectrum element distribution results. The maximum continuous tellurium-rich length of the tellurium-rich region and the minimum width of the copper-based continuous region between adjacent tellurium-rich regions are counted along the original interface direction. When there is a copper-based continuous region with a width of not less than 2 micrometers between adjacent tellurium-rich regions, the adjacent tellurium-rich regions are counted as being separated by the copper-based continuous region. When the maximum continuous tellurium-rich length in the original interface direction after hot pressing-shear composite densification is lower than the corresponding value after the restricted reaction pretreatment, it is determined that the tellurium-containing reaction connection region has formed a discrete state.

[0050] In the pore area fractional analysis, scanning electron microscopy (SEM) was used to observe the cross-sectional images of the original interface region or the corresponding sampling region before and after interface stabilization treatment at a uniform magnification. At least three observation fields were selected for each sample. Continuous pores and residual micropores were identified through image segmentation, and the proportion of pore area to the corresponding statistical region area was calculated. During pore identification, the results of energy dispersive spectroscopy (EDS) were used to exclude low-signal areas of Te and polishing marks, avoiding misclassification of tellurium-rich region boundaries or sample preparation defects as pore regions.

[0051] In the determination of the continuous contact state of copper-based composites, regions with continuous pores are first excluded by scanning electron microscopy images. Then, the elemental distribution of Cu is confirmed by energy dispersive spectroscopy to be continuously distributed across the original interface region and the tellurium-rich region is continuously separated by the copper substrate. When the electron backscatter diffraction orientation identification results are used for auxiliary confirmation, the results are only used to help exclude obviously uncontacted regions and regions with severe orientation discontinuities. Individual grain orientation consistency is not used as the basis for determining the continuous contact state of copper-based composites.

[0052] In the mechanical property testing, tensile specimens were cut along the processing direction of the finished product, and room temperature tensile tests were conducted on the examples and comparative examples using the same dimensions, sampling direction, and testing conditions. At least three parallel specimens were set for each sample, the tensile speed was 1 mm / min, and the tensile strength and elongation after fracture were tested. The average value of the parallel specimens was taken as the mechanical property test result for that sample.

[0053] In the chip-breaking performance test, dry cutting tests were conducted on the examples and comparative examples under the same turning conditions. The resulting finished products were machined into bar samples suitable for turning, with a bar diameter of 10 mm; the turning speed was 80 m / min, the feed rate was 0.10 mm / rpm, the depth of cut was 0.50 mm, and the continuous cutting length was 100 mm. The chips formed during the cutting process were collected, and the proportion of chips with a length not greater than 10 mm to the total chip mass was counted, and this proportion was taken as the short chip rate. Each sample underwent no less than three parallel turning tests, and the average value was taken as the chip-breaking performance test result.

[0054] Reference Figure 10 During the cutting process, the discrete tellurium-rich sections in the lead-free, easily machinable beryllium copper alloy obtained by this invention can serve as local crack triggering locations, causing the chips to segment near these local tellurium-rich sections, forming short or discontinuous chips. Simultaneously, the continuous copper matrix between the discrete tellurium-rich sections maintains its overall load-bearing continuity. In contrast, when tellurium-rich cracking triggering is insufficient or the continuous distribution of tellurium-rich regions is unreasonable, continuous chip curling is easily formed during cutting, resulting in inadequate chip breaking performance improvement, or a decrease in load-bearing performance due to continuous brittle channels.

[0055] When further confirmation of the phase composition of tellurium-rich regions is required, the phase composition of the tellurium-rich regions is verified. Specifically, at least one of electron probe microanalysis, transmission electron microscopy, selected area electron diffraction, and X-ray diffraction is used to analyze the Te-enriched regions. If phase composition verification is not performed, only regions with Te content higher than that of the adjacent continuous copper matrix are described as tellurium-rich regions, without limiting them to a specific copper telluride phase.

[0056] Reference Figure 9 This invention differs significantly from the comparative example of a continuous, monolithic tellurium-containing layer in the morphology of the tellurium-rich network. In this invention, the discontinuously patterned tellurium-containing reactive micro-interlayer, after confined reaction, hot-pressing-shear composite densification, and interface stabilization treatment, forms multiple discrete tellurium-rich segments. These segments are continuously separated by a copper substrate. Cutting cracks can be triggered near local tellurium-rich segments, while the overall load-bearing path is borne by the continuous copper substrate. In contrast, the comparative example of a continuous, monolithic tellurium-containing layer tends to form a continuous tellurium-rich network along the original interface direction, causing the tellurium-rich region to form a continuous brittle channel along the interface direction, resulting in coupling between the cutting fracture path and the load-bearing path.

[0057] Through the above-described preparation method and detection criteria, this invention enables the formation of discrete tellurium-rich segments within a continuous copper substrate. These discrete tellurium-rich segments serve as localized fracture trigger points during cutting, facilitating chip fragmentation near these segments. Simultaneously, since these tellurium-rich segments do not form a continuous tellurium-rich network along the original interface direction, adjacent tellurium-rich segments maintain continuous contact with the copper substrate. Therefore, the overall load-bearing path of the material is primarily borne by the continuous copper substrate. Thus, this invention achieves a balance between chip-breaking performance and mechanical load-bearing capacity under lead-free conditions.

[0058] In both the embodiments and comparative examples of this invention, a 1.20 mm thick beryllium copper strip is used as the beryllium copper matrix unit. The beryllium copper strip comprises, by mass percentage, 1.80% beryllium, 0.20% zinc, 0.10% cobalt, 0.15% nickel, 0.05% iron, 0.04% aluminum, and 0.03% silicon, with the balance being copper and unavoidable impurities. The lead content is no greater than 0.005%, and the tellurium content is no greater than 0.002%. Subsequent processing includes hot extrusion, drawing, cold working, and a two-stage aging treatment. The hot extrusion temperature is 740 degrees Celsius, the extrusion ratio is 10:1, the cumulative deformation during cold working is 33%, the first-stage aging temperature is 315 degrees Celsius with a holding time of 2 hours, and the second-stage aging temperature is 390 degrees Celsius with a holding time of 1.5 hours.

[0059] Example 1: A discontinuously patterned tellurium-containing reactive microlayer was formed between two adjacent beryllium copper substrate units. The tellurium-containing reactive microlayer was formed by locally loading a tellurium-containing dry film onto the surface of a 25-micrometer-thick copper foil carrier. The local reaction domains adopted an island-shaped pattern with an equivalent diameter of 130 micrometers, a center-to-center spacing of 180 micrometers, and a local reaction domain area ratio of 31%. The tellurium loading per unit area was 0.074 mg / cm². After the assembled billet underwent a restricted reaction pretreatment at 565°C for 12 minutes, it was held at 735°C and 27 MPa for 8 minutes with a 1.5 mm unidirectional shear displacement applied. Then, it was held at 710°C and 9 MPa for 20 minutes for interface stabilization treatment. Subsequent processing was then completed to obtain a lead-free, free-machining, and easily machinable beryllium copper alloy.

[0060] Test results showed that the tellurium content in the finished product was 0.0038%, and the lead content was less than 0.005%. The Te enrichment zone formed discrete tellurium-rich segments distributed within the continuous copper matrix, and no continuous tellurium-rich network was observed along the original interface direction. The maximum continuous tellurium-rich segment length along the original interface direction was 72 micrometers, the minimum width of the continuous copper matrix region between adjacent tellurium-rich segments was 3.4 micrometers, and the porosity fraction was 0.28%. The tensile strength was 1185 MPa, the elongation after fracture was 8.2%, and the short chip rate was 85.6%.

[0061] Example 2: Discontinuously patterned tellurium-containing reactive micro-layers were formed between two adjacent beryllium copper substrate units. The local reaction domains adopted an island-like pattern with an equivalent diameter of 130 micrometers, a center-to-center spacing of 180 micrometers, and a local reaction domain area ratio of 31%. The tellurium loading per unit area was 0.074 mg / cm². After the assembled billet underwent a restricted reaction pretreatment at 565°C for 12 minutes, it was held at 735°C and 27 MPa for 8 minutes, and then subjected to a first-direction shear displacement of 0.9 mm and a second-direction shear displacement of 0.8 mm were applied sequentially. Finally, it was held at 710°C and 9 MPa for 20 minutes for interface stabilization treatment. Subsequent processing was then completed to obtain a lead-free, free-machining, and easily machinable beryllium copper alloy.

[0062] Test results showed that the tellurium content in the finished product was 0.0037%, and the lead content was less than 0.005%. The Te enrichment area was divided into multiple unconnected segments by a continuous copper-based zone, failing to form a continuous tellurium-rich network along the original interface direction. The maximum continuous tellurium-rich length along the original interface direction was 58 micrometers, the minimum width of the continuous copper-based zone between adjacent tellurium-rich segments was 3.8 micrometers, and the porosity fraction was 0.22%. The tensile strength was 1196 MPa, the elongation after fracture was 8.3%, and the short chip rate was 87.8%.

[0063] Example 3: A discontinuously patterned tellurium-containing reactive micro-layer was formed between two adjacent beryllium copper substrate units. The local reaction domains adopted a segmented pattern with a segment length of 190 μm, a width of 40 μm, and a segment spacing of 120 μm. The long axis of the segments was arranged along the shear direction. The local reaction domain area accounted for 36%, and the tellurium loading per unit area was 0.188 mg / cm². After the assembled billet underwent a restricted reaction pretreatment at 575°C for 15 minutes, it was held at 745°C and 30 MPa for 10 minutes with a unidirectional shear displacement of 1.8 mm. Then, it was held at 715°C and 10 MPa for 25 minutes for interface stabilization treatment. Subsequent processing was then completed to obtain a lead-free, free-machining, and easily machinable beryllium copper alloy.

[0064] Test results showed that the tellurium content in the finished product was 0.0093%, and the lead content was less than 0.005%. The segmented local reaction zones were transformed into short, granular, discrete tellurium-rich segments after treatment, without forming a continuous tellurium-rich network along the original interface direction. The maximum continuous tellurium-rich length along the original interface direction was 81 micrometers, the minimum width of the copper-based continuous region between adjacent tellurium-rich segments was 3.1 micrometers, and the porosity fraction was 0.31%. The tensile strength was 1168 MPa, the elongation after fracture was 7.9%, and the short chip rate was 91.2%.

[0065] Example 4: Multiple assembled preforms were prepared using the same beryllium copper matrix unit and tellurium-containing reactive micro-interlayer as in Example 1. Each assembled preform underwent a restricted reaction pretreatment at 565°C for 12 minutes. Samples were taken from one group after the restricted reaction pretreatment, and from the other groups after the uniaxial shear displacement reached 0.5 mm, 1.0 mm, and 1.5 mm and pressure holding was completed. Samples were also taken from another group after the 1.5 mm uniaxial shear displacement was completed and then subjected to an interface stabilization treatment at 710°C, 9 MPa for 20 minutes.

[0066] The test results showed that after the restricted reaction pretreatment, the Te enrichment region was mainly located at the corresponding position of the island-like local reaction domain, with a maximum continuous tellurium enrichment length of 126 μm in the original interface direction. After shear displacement reached 0.5 mm, 1.0 mm, and 1.5 mm, the maximum continuous tellurium enrichment length in the original interface direction decreased to 104 μm, 87 μm, and 68 μm, respectively. After interface stabilization treatment, the pore area fraction decreased from 0.58% to 0.27%, and the newly formed copper-based contact area between adjacent dispersed tellurium enrichment sections remained continuously distributed. No continuously penetrating tellurium enrichment network along the original interface direction was observed.

[0067] Comparative Example 1: A copper foil carrier with a thickness of 25 micrometers and without a tellurium dry film was placed between two adjacent beryllium copper substrate units and stacked to form an assembled blank. The assembled blank was heat-treated at 565 degrees Celsius for 12 minutes, then held at 735 degrees Celsius and 27 MPa for 8 minutes with a unidirectional shear displacement of 1.5 mm, and then stabilized at 710 degrees Celsius and 9 MPa for 20 minutes. Subsequent processing was then completed to obtain a beryllium copper alloy.

[0068] Test results showed that the tellurium content in the finished product was less than 0.002%, and the lead content was less than 0.005%; no discrete tellurium-rich sections formed by the transformation of tellurium-containing reactive micro-layers were observed. The porosity fraction was 0.25%; the tensile strength was 1210 MPa, the elongation after fracture was 8.9%, and the short chip rate was 47.3%.

[0069] Comparative Example 2: A continuous, full-surface tellurium-containing layer was formed between two adjacent beryllium copper substrate units. This continuous, full-surface tellurium-containing layer was formed by loading a tellurium-containing dry film onto the surface of a 25-micrometer-thick copper foil carrier, with a tellurium loading of 0.074 mg / cm². The assembled blank was pretreated at 565°C for 12 minutes, then pressurized at 735°C and 27 MPa for 8 minutes with a 1.5 mm unidirectional shear displacement, followed by stabilization treatment at 710°C and 9 MPa for 20 minutes. Subsequent processing was then completed to obtain the beryllium copper alloy.

[0070] Test results showed that the tellurium content in the finished product was 0.0039%, and the lead content was less than 0.005%. The Te enrichment area was continuously or semi-continuously distributed along the original interface direction, and a continuous Te enrichment band was formed in some observation fields, spanning the statistical field of view. The maximum continuous tellurium enrichment length along the original interface direction was 263 micrometers, and the porosity fraction was 0.36%. The tensile strength was 1041 MPa, the elongation after fracture was 5.5%, and the short chip rate was 95.4%.

[0071] Comparative Example 3: Discontinuously patterned tellurium-containing reactive micro-layers were set between two adjacent beryllium copper matrix units. The local reaction domains adopted an island-like pattern with an equivalent diameter of 130 micrometers, a center-to-center spacing of 180 micrometers, and a local reaction domain area ratio of 31%. The tellurium loading per unit area was 0.074 mg / cm². After the assembled billet underwent a restricted reaction pretreatment at 565°C for 12 minutes, it was hot-pressed and densified at 735°C and 27 MPa for 8 minutes without applying shear displacement during the pressing process. Then, it was held at 710°C and 9 MPa for 20 minutes for interface stabilization treatment, followed by subsequent processing to obtain a beryllium copper alloy.

[0072] Test results showed that the tellurium content in the finished product was 0.0038%, and the lead content was less than 0.005%. Te enrichment zones were formed at the corresponding locations of local reaction sites, with some Te enrichment zones retaining relatively long continuous sections. The maximum continuous tellurium-rich section length in the original interface direction was 147 micrometers, the minimum width of the copper-based continuous zone between adjacent tellurium-rich sections was 2.1 micrometers, and the porosity fraction was 0.42%. The tensile strength was 1108 MPa, the elongation after fracture was 6.8%, and the short chip rate was 78.6%.

[0073] Comparative Example 4: Discontinuously patterned tellurium-containing reactive micro-layers were set between two adjacent beryllium copper substrate units. The local reaction domains adopted an island-like pattern with an equivalent diameter of 130 micrometers, a center-to-center spacing of 180 micrometers, and a local reaction domain area ratio of 31%. The tellurium loading per unit area was 0.074 mg / cm². After the assembled billet underwent a restricted reaction pretreatment at 565°C for 12 minutes, it was then subjected to a pressure hold of 735°C and 27 MPa for 8 minutes with a 1.5 mm unidirectional shear displacement. Subsequently, without interface stabilization treatment, subsequent processing was directly completed to obtain a beryllium copper alloy.

[0074] Test results showed that the tellurium content in the finished product was 0.0037%, and the lead content was less than 0.005%. Dispersed tellurium-rich zones were formed in the finished product, with the longest continuous tellurium-rich zone length in the original interface direction being 75 micrometers. However, there were many residual pores at the shear separation boundary. The pore area fraction was 0.74%; the tensile strength was 1093 MPa, the elongation after fracture was 6.0%, and the short chip rate was 84.8%.

[0075] Comparative Example 5: A tellurium-containing beryllium copper base material was prepared according to the target tellurium content of the finished product. The tellurium-containing beryllium copper base material, by mass percentage, includes 1.80% beryllium, 0.0060% tellurium, 0.20% zinc, 0.10% cobalt, 0.15% nickel, 0.05% iron, 0.04% aluminum, and 0.03% silicon, with the balance being copper and unavoidable impurities, wherein the lead content is not greater than 0.005%. The tellurium-containing beryllium copper base material was smelted, cast, homogenized, hot-rolled, and cold-rolled to produce a tellurium-containing beryllium copper strip with a thickness of 1.20 mm. Subsequent processing was then carried out to obtain a beryllium copper alloy.

[0076] Test results showed that the tellurium content in the finished product was 0.0061%, and the lead content was less than 0.005%. Te was distributed as a whole in the alloy, without forming discrete tellurium-rich sections concentrated along the original interface region due to the transformation of discontinuous patterned tellurium-containing reactive micro-layers. Local Te-rich areas were randomly distributed. The tensile strength was 1125 MPa, the elongation after fracture was 6.7%, and the short chip rate was 76.2%.

[0077] Comparative Example 6: Discontinuously patterned tellurium-containing reactive micro-layers were set between two adjacent beryllium copper matrix units. The local reaction domains adopted an island-like pattern with an equivalent diameter of 130 micrometers, a center-to-center spacing of 180 micrometers, and a local reaction domain area ratio of 31%. The tellurium loading per unit area was 0.074 mg / cm². The assembled billet was not subjected to restricted reaction pretreatment. It was directly pressurized at 735°C and 27 MPa for 8 minutes with a 1.5 mm unidirectional shear displacement, and then held at 710°C and 9 MPa for 20 minutes for interface stabilization treatment. Subsequent processing was then completed to obtain the beryllium copper alloy.

[0078] Test results showed that the tellurium content in the finished product was 0.0038%, and the lead content was less than 0.005%. The distribution of Te enrichment zones in the corresponding local reaction areas was uneven, and some tellurium-rich sections had residual porosity with adjacent copper-based regions. The maximum continuous tellurium-rich length in the original interface direction was 102 micrometers, with a porosity fraction of 0.69%. The tensile strength was 1082 MPa, the elongation after fracture was 5.9%, and the short chip rate was 80.1%.

[0079] Table 1 Key test results of the final products of the examples and comparative examples Example 1 0.0038 72 0.28 1185 8.2 85.6 Example 2 0.0037 58 0.22 1196 8.3 87.8 Example 3 0.0093 81 0.31 1168 7.9 91.2 Comparative Example 1 ＜0.002 No tellurium-rich section formed 0.25 1210 8.9 47.3 Comparative Example 2 0.0039 263 0.36 1041 5.5 95.4 Comparative Example 3 0.0038 147 0.42 1108 6.8 78.6 Comparative Example 4 0.0037 75 0.74 1093 6 84.8 Comparative Example 5 0.0061 not applicable Not included in the original interface statistics 1125 6.7 76.2 Comparative Example 6 0.0038 102 0.69 1082 5.9 80.1 The test results show that the embodiment did not form a continuous tellurium-rich layer extending along the original interface direction in the low tellurium content range, but instead controlled the tellurium-rich region to be discretely distributed. Compared with the sample with a continuous tellurium-rich layer on the entire surface, the maximum continuous tellurium-rich length in the original interface direction of the embodiment was reduced by about 69% to 78%, but the tensile strength was increased by about 12% to 15%, and the elongation after fracture was increased by about 44% to 51%. This indicates that although a continuous tellurium-rich layer is beneficial for chip breaking, it weakens the continuous load-bearing path of the copper substrate. The present invention avoids this continuous embrittlement along the interface direction by using discontinuously patterned tellurium-rich reactive micro-layers to continuously separate the tellurium-rich region with the copper substrate. Compared with the sample without tellurium-containing reactive micro-interlayers, the short chip rate of the embodiment was increased by about 81% to 93%, indicating that the discrete tellurium-rich section can provide an effective local fracture triggering location during the cutting process; however, compared with the sample with tellurium added as a whole, the embodiment can still increase the short chip rate by about 12% to 20%, while the tensile strength and elongation after fracture are increased by about 4% to 6% and 18% to 24%, respectively, indicating that the effect of the present invention does not come from the total amount of tellurium itself, but from the microstructure of tellurium after controlled distribution in the original interface region.

[0080] Further examining the impact of process steps on the microstructure, without applied shear displacement, the tellurium-rich region still retains a relatively long continuous segment. However, in the example, the maximum continuous tellurium-rich length in the original interface direction is reduced by approximately 45%–61%, indicating that hot-pressing-shear composite densification is not a typical pressure-holding densification process, but rather a crucial treatment that promotes thinning, separation, and discretization of the tellurium-containing reaction connection zone. Without the restricted reaction pretreatment, the maximum continuous tellurium-rich length and porosity in the original interface direction are significantly degraded, while in the example, they are reduced by approximately 21%–43% and 55%–68%, respectively. This indicates that the restricted reaction pretreatment provides a stable local initial reaction basis for subsequent shear discretization. Without the interface stabilization treatment, although dispersed tellurium-rich segments can be formed, residual porosity is significantly increased. In the example, the porosity area fraction is reduced by approximately 58%–70%, indicating that the interface stabilization treatment stabilizes the newly formed copper-based contact area and reduces residual porosity at the shear separation boundary.

[0081] Therefore, this invention does not simply achieve machinability by adding tellurium, nor does it rely on sacrificing strength to improve the short chip rate by a continuous tellurium-rich layer. Instead, it achieves a balance between the chip-breaking performance and mechanical load-bearing performance of lead-free beryllium copper alloys by continuously combining discontinuous patterned tellurium-containing reaction micro-interlayers, restricted reaction pretreatment, hot-pressing-shear composite densification, and interface stabilization treatment. This allows the discrete tellurium-rich sections to take on the chip-breaking triggering role, while the continuous copper matrix maintains its load-bearing role.

[0082] The above description is only a specific embodiment of this disclosure, but the protection scope of this disclosure is not limited thereto. The protection scope of this disclosure should be determined by the protection scope of the claims.

Claims

1. A method for preparing a lead-free, free-machining, and easily machinable beryllium copper alloy, characterized in that, include: Prepare beryllium copper matrix units that do not contain the intentionally added tellurium and lead elements; The tellurium loading per unit area is determined according to the target tellurium content of the finished product, and a discontinuously patterned tellurium-containing reactive micro-interlayer is set between adjacent beryllium copper substrate units. The tellurium-containing reactive micro-interlayer is composed of multiple spaced local reaction domains. A restricted reaction pretreatment is performed on the assembled preform containing the tellurium-containing reaction micro-interlayer to form a local initial reaction zone between the local reaction domain and the adjacent copper-based region; Hot pressing-shear composite densification is performed on the assembled green body that has undergone restricted reaction pretreatment, so that the local initial reaction zone is transformed into a tellurium-containing reaction connection zone, and the tellurium-containing reaction connection zone is thinned, separated and discretized under the combined action of compression and shear, resulting in a new interface green body with dispersed tellurium-rich sections. An interface stabilization treatment is performed on the newly formed interface billet to maintain the continuous distribution of the newly formed copper-based contact area between adjacent dispersed tellurium-rich sections and reduce the residual porosity of the original interface area, thereby obtaining a copper-based continuous contact composite billet. The copper-based continuous contact composite billet is subjected to plastic working, cold working and aging treatment to obtain a lead-free, free-cutting and easy-to-machine beryllium copper alloy; The lead-free free-machining beryllium copper alloy comprises a continuous copper matrix and discrete tellurium-rich segments distributed within the continuous copper matrix. The discrete tellurium-rich segments do not form a continuous tellurium-rich network along the original interface direction, and the tellurium content of the lead-free free-machining beryllium copper alloy, as measured by inductively coupled plasma atomic emission spectrometry, is 0.0030% to 0.0100%.

2. The preparation method according to claim 1, characterized in that, The tellurium-containing reactive microlayer is formed by locally loading a tellurium-containing dry film onto the surface of a copper foil carrier. The thickness of the copper foil carrier is 10 micrometers to 40 micrometers, the area ratio of the local reactive domain is 20% to 40%, and the tellurium loading per unit area of ​​the tellurium-containing reactive microlayer is 0.06 mg / cm² to 0.20 mg / cm².

3. The preparation method according to claim 2, characterized in that, The local reaction domain adopts either an island pattern or a strip pattern; When the local reaction domain adopts an island pattern, the equivalent diameter of the island pattern is 60 micrometers to 160 micrometers, and the center-to-center spacing is 90 micrometers to 220 micrometers. When the local reaction domain adopts a strip pattern, the length of the strip pattern is 120 micrometers to 240 micrometers, the width is 20 micrometers to 60 micrometers, the spacing between the strips is 80 micrometers to 160 micrometers, and the long axis of the strip pattern is arranged along the shear direction.

4. The preparation method according to claim 1, characterized in that, The restricted reaction pretreatment is carried out under a protective atmosphere, with a treatment temperature of 540°C to 590°C and a holding time of 5 minutes to 30 minutes, so that the local reaction domain and the adjacent copper-based region undergo a local reaction, and the local initial reaction zone does not form a continuous reaction layer along the original interface direction.

5. The preparation method according to claim 1, characterized in that, The hot-pressing-shear composite densification is carried out at 700°C to 760°C and 15 MPa to 35 MPa, with a holding time of 5 minutes to 15 minutes, and either a unidirectional shear path or a cross-shear path is used. When using a unidirectional shear path, apply a unidirectional shear displacement of 0.5 mm to 2.5 mm; When using a cross-shear path, apply a first-direction shear displacement of 0.5 mm to 1.5 mm and a second-direction shear displacement of 0.4 mm to 1.2 mm in sequence.

6. The preparation method according to claim 1, characterized in that, The thinning, separation, and discretization of the tellurium-containing reaction connection region were determined by cross-sectional scanning electron microscopy and energy dispersive spectroscopy elemental distribution detection. When the tellurium-rich region corresponding to the same local reaction domain is divided into two or more non-connected segments by a copper-based continuous region, and the width of the copper-based continuous region between adjacent tellurium-rich regions is not less than 2 micrometers, the tellurium-containing reaction connection region forms a separated state. When the maximum continuous tellurium-rich length in the original interface direction of the tellurium-rich region within the statistical area is lower than the corresponding value after the restricted reaction pretreatment, the tellurium-containing reaction connection region forms a discretized state.

7. The preparation method according to claim 1, characterized in that, The interface stabilization treatment is carried out at 680°C to 730°C and 5 MPa to 15 MPa, with a holding time of 10 minutes to 60 minutes. The interface stabilization treatment targets the newly formed copper-based contact area and the residual pores at the shear separation boundary formed after hot pressing-shear composite densification. After the interface stabilization treatment, the newly formed copper-based contact area between adjacent dispersed tellurium-rich sections remains continuously distributed, and the discrete tellurium-rich sections do not form a continuous tellurium-rich network along the original interface direction.

8. The preparation method according to claim 1, characterized in that, The plastic processing includes hot extrusion and drawing. The hot extrusion temperature is 720°C to 760°C, and the extrusion ratio is 6:1 to 14:

1. The cumulative deformation of the cold working is 20% to 45%. The aging treatment includes a first-stage aging and a second-stage aging. The first-stage aging temperature is 280°C to 340°C, and the second-stage aging temperature is 360°C to 430°C.

9. The preparation method according to claim 1, characterized in that, The continuous contact state of the copper-based matrix in the original interface region was determined by scanning electron microscopy pore identification and energy spectrum elemental distribution identification. The copper-based continuous contact region of the original interface region is only included when the corresponding region simultaneously meets the following conditions: there are no continuous pores, copper elements are continuously distributed across the original interface, and the tellurium-rich region is continuously separated by the copper-based matrix. When using electron backscatter diffraction orientation identification for auxiliary confirmation, the uniformity of individual grain orientations is not used as the basis for determining the continuous contact state of the copper substrate in the original interface region.

10. A lead-free, free-machining, and easily machinable beryllium copper alloy, characterized in that, Prepared by any one of claims 1 to 9, comprising, by mass percentage: 0.20%–2.00% beryllium, 0.0030%–0.0100% tellurium, 0.10%–0.30% zinc, 0.05%–0.60% total cobalt and nickel, ≤0.15% iron, ≤0.15% aluminum, ≤0.10% silicon, with the balance being copper and unavoidable impurities, wherein the lead content is not greater than 0.005%; The lead-free, free-machining beryllium copper alloy comprises a continuous copper matrix and discrete tellurium-rich segments distributed within the continuous copper matrix. The Te content in the discrete tellurium-rich segments is higher than the Te content in the adjacent continuous copper matrix. The discrete tellurium-rich segments are in at least one of the following forms: short strips, islands, and granules. Furthermore, the discrete tellurium-rich segments do not form a continuous tellurium-rich network along the original interface direction.

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