KR20240100423A - electrode wire - Google Patents

Abstract

The present invention relates to an electrode wire comprising a metal core (10) extending along a longitudinal axis, and a coating on the metal core comprising one or more copper-zinc gamma phase alloy regions (30-32), wherein these regions Each is formed solely from a copper-zinc gamma phase alloy and the zinc concentration within each of these copper-zinc gamma phase alloy regions is greater than 65.4 atomic percent at an ambient temperature of 25°C. More than 50% of the copper-zinc gamma phase alloy regions 30-32 are located less than 1 μm from the outer surface of the electrode wire.

Description

electrode wire

The present invention relates to an electrode wire that can be used as an electrode wire for electro-erosion processing. The invention also relates to a method of manufacturing such electrode wire.

Electrode wires are used in electro-erosion processing machines to cut metal or electrically conductive materials by electro-erosion.

The well-known electro-erosion machining or spark erosion method allows material to be removed from electrically conductive parts by generating sparks in the machining area between the workpiece and electrically conductive electrode wires. The electrode wire is continuously unwound near the part along the length of the wire held by the guide, and it gradually moves laterally toward the part by the transverse translation of the wire guide or the translation of the part.

A generator connected to the electrode wire by electrical contacts away from the machining area creates an appropriate potential difference between the electrode wire and the conductive component to be machined. The processing area between the electrode wire and the component is immersed in a suitable dielectric fluid. The potential difference causes sparks to appear between the electrode wire and the workpiece that slowly erode the part and the electrode wire. Unwinding the electrode wire in the longitudinal direction can maintain a sufficient wire diameter and prevent the electrode wire from being broken in the processing area. The relative movement of the wire and the part in the transverse direction allows, where applicable, to cut the part or treat its surface.

Particles separated from electrode wires and components by sparks are dispersed in the dielectric fluid and released.

To achieve precision machining, especially for producing small radius edge cuts, it is necessary to use small diameter wires that can withstand significant mechanical tensile strengths to tension the machining area and limit the amplitude of any vibrations.

Most modern electro-erosion processing machines are designed to use metal wires, typically with a diameter of 0.25 mm and tensile strengths ranging from 400 N/mm ² to 1,000 N/mm ² .

When a spark occurs between an electrode wire and a component, the surface of the electrode wire is suddenly heated to a very high temperature and for a short period of time. As a result, at the site of spark generation, the material of the surface layer of the electrode wire transitions from a solid state to a liquid or gaseous state and moves to the surface of the electrode wire and/or is released into the dielectric fluid. It can be seen that the outer surface of the electrode wire where the spark reaches is generally deformed to take the shape of a slightly concave crater and has an area where the material is melted and then solidified again.

It has been observed that the efficiency of the spark associated with electro-erosion mainly depends on the properties and topography of the surface layer of the electrode wire. for teeth,

- a core made of one or more metals or alloys that ensure good mechanical strength and good current conduction to maintain the mechanical tensile strength of the wire; and

- a coating made of one or more different metals or alloys and/or having a specific surface shape, e.g. cracks, which ensures better efficiency of electro-erosion, e.g. faster erosion rates.

Significant advances in electro-erosion efficiency have been achieved by the use of electrode wires comprising .

For example, application US 5945010 A describes an electrode wire with a brass core covered with a copper-zinc gamma phase alloy layer, optionally overlaid by a copper-zinc epsilon phase alloy layer. This application teaches that these copper-zinc gamma phase alloy layers allow for improved performance of electrode wires. In particular, this application describes a No. 3 electrode wire specimen comprising a copper-zinc gamma phase alloy layer overlaid by a copper-zinc epsilon phase alloy surface layer. The thickness of the surface layer is 3 μm. The zinc concentration of the copper-zinc gamma phase alloy layer is 68 atomic percent. This application also describes a No. 4 electrode wire specimen comprising a copper-zinc gamma phase alloy surface layer. In this case, the zinc concentration of the copper-zinc gamma phase alloy surface layer is 65 atomic percent.

The prior art is also known from the documents US 2017/259361 A, US 2008/179296 A1 and US 2009/025959 A1.

The electrode wire of application US 5945010 A has high performance capabilities. However, it is still desirable to obtain electrode wires with better performance, especially electrode wires that exhibit improved erosion efficiency and/or faster processing speeds.

The present invention aims to meet these requirements by proposing an electrode wire as claimed in claim 1.

A further object of the invention is a method for producing the claimed electrode wire.

The invention is provided by way of non-limiting example only and will be better understood by reading the following description with reference to the drawings, in which:
- Figure 1 is a schematic diagram of a cross section of an electrode wire;
- Figure 2 is a flow chart of the method for manufacturing the electrode wire of Figure 1;
- Figure 3 is a black and white photograph of a portion of the cross-section of the wire before the drawing step, produced according to the method of Figure 2;
- Figure 4 is an image of a portion of a cross-section of an electrode wire after the drawing step, produced according to the method of Figure 2;
Throughout these drawings, like reference numerals are used to represent like elements. Throughout the remainder of this description, features and functions well known to those skilled in the art are not described in detail.

Definitions of specific terms are provided below in Chapter I. In Chapter II, detailed examples of embodiments are described with reference to the drawings. Chapter III then introduces alternative embodiments of this embodiment. Finally, Chapter IV introduces the advantages of various embodiments.

Chapter I: Definitions and Terminology

The expression “element made from material A” or “element made from material A” means an element in which material A accounts for at least 90% by weight of this element, preferably at least 95% by weight or 98% by weight of this element. do.

“Copper-zinc alloy” means an alloy formed solely of copper and zinc, excluding inevitable impurities.

“Phase” of a copper-zinc alloy means a solid phase of the copper-zinc alloy that exhibits a particular crystallographic structure. More specifically, the phases of the copper-zinc system are distinct from each other in terms of their composition and their specific crystallographic structures. This specific crystallographic structure allows the phase of copper-zinc alloy to be distinguished from a simple mixture of fine copper and zinc particles with the same overall composition. Typically, the known phases of copper-zinc alloys are alpha phase, beta phase, gamma phase, delta phase, epsilon phase and eta phase. The specific crystallographic structure of a phase can be identified using a variety of means. For example, optical microscopy or metallographic micrographs of polished samples show various shades of color for each phase, as long as the sample has been properly attacked. Therefore, in order to distinguish the gamma phase from the epsilon phase, an attack is performed with “Nital”, a 3% solution of nitric acid diluted in ethanol. The gamma phase appears gray when zinc is deficient, and gray with a brown tint when zinc-rich. The epsilon phase appears a darker brown color. It is also possible to distinguish the gamma phase from the epsilon phase by observing the sample with a scanning electron microscope using a backscattered electron detector. It is also possible to identify the phase of the sample through X-ray diffraction. In this case, the wire sample is placed under an incident beam of X-rays with the correct wavelength. For example, the K _α line of copper with an average wavelength of 0.1541 nm is used. The intensity of the diffracted light is evaluated for each diffraction angle. The gamma phase has a known If a copper-zinc alloy does not crystallize in at least one of the alpha, beta, gamma, delta, epsilon, or eta phases, it is amorphous and its X-ray diffraction spectrum shows flattened bumps rather than raised peaks. ).

At a specific temperature, the various phases of the copper-zinc alloy each correspond to a specific range of zinc concentrations. The zinc concentration in each of these specific ranges varies with temperature. The zinc concentration of the phase of the sample can be obtained by compositional trace analysis. Composition trace analysis is performed using a scanning electron microscope equipped with a spectroscopic probe. For example, an electron beam accelerated in a 20 kV electric field impacts the surface of the sample, causing X-rays to be emitted. These X-rays have an energy spectrum that characterizes the composition of the surface of the sample with which the electron beam impinges. The spectrum of X-rays emitted by the surface of the sample is measured using an energy-dispersive spectroscopy (EDS) or wavelength-dispersive spectroscopy (WDS) analytical probe. Using an algorithm, the elements to be analyzed can be selected (thus eliminating the influence of any impurities) and the composition of the sample struck by the electron beam can be calculated based on the measured spectrum. It should be noted that, due to the interaction between X-rays and the material, the volume analyzed by EDS (or WDS) is typically approximately 1 cubic micrometer. At the boundary between the two phases, an average concentration can be measured that is not actually present in either phase. In these cases the concentrations stated relate to the pure phase in the analysis volume. The area over which the concentration is measured is larger than a micrometer-sized cube.

The expression “the zinc concentration in the copper-zinc alloy regions is greater than X atomic percent” means that the average zinc concentration in these regions is greater than X atomic percent. The average concentration is obtained, for example, by measuring zinc concentration at various sites within these regions and then averaging these concentration measurements. The sites at which measurements are performed are equally located at the site where the concentration is expected to be lowest, where the concentration is expected to be close to the average, and where the concentration is expected to be maximum. For this purpose, typically the area at which measurements are performed is distributed along an axis transverse to the axis of the electrode wire.

The expression “electrically conductive” means a material having an electrical conductivity at 20° C. of greater than 10 ⁶ S/m, preferably greater than 10 ⁷ S/m.

The longitudinal axis of the wire is the axis that is mainly used as a reference when the wire is extended.

The expression “cross-section” means a cross-section of the electrode wire perpendicular to the longitudinal axis of the electrode wire.

The expression “layer of electrode wire” means the annular layer of electrode wire located between the inner and outer circular boundaries, in each cross-section of the electrode wire. In reality, these boundaries are not necessarily perfect circles. However, as an initial approximation, in this literature, this boundary is likened to a circle. These circular boundaries are all centered on the longitudinal axis of the electrode wire. The inner circular boundary is the boundary of the layer closest to the longitudinal axis of the electrode wire. In contrast, the outer circular boundary is the boundary of the layer furthest from the longitudinal axis of the electrode wire. Between these inner and outer circular boundaries, the phase of the copper-zinc alloy is either homogeneous or is formed by random fusion of various phases of the copper-zinc alloy. In contrast, at the inner and outer circular boundaries, the chemical composition and/or crystallographic form changes abruptly.

A “homogeneous” layer is a layer formed by a single phase of a copper-zinc alloy.

A “uniform” layer means a layer formed of a material that, in the cross-section of the wire, extends continuously or substantially continuously around the axis of the wire and within this layer. Accordingly, a homogeneous layer does not contain numerous cracks that, in the cross-section of the wire, divide the layer into multiple regions separated from each other by numerous radial cracks. “Numerous radial cracks” means more than approximately 10 radial cracks that, in cross section, divide the layer in question into approximately 10 zones that are mechanically isolated from each other by these radial cracks.

In contrast, the term “cracked layer” means a layer comprising numerous cracks that, in the cross-section of the wire, divide the layer into a number of regions separated from each other by numerous radial cracks.

The expression “metallic surface layer”, or simply “surface layer”, means the copper-zinc alloy or zinc layer of the electrode wire, which is the outermost layer of the electrode wire. This metal surface layer may include a thin oxide film on its surface. Typically, this oxide film consists mainly of zinc oxide, zinc hydroxide, zinc carbonate, as well as possible residues such as drawing lubricant residues. The outer surface of this metal surface layer therefore coincides with the outer surface of the electrode wire, in the absence of a thin oxide film, or is separated from the outer surface of the electrode wire only by this thin oxide film.

A “radial crack” is a crack that extends primarily in a radial direction within the cross-section of the electrode wire.

The expression “ambient temperature” means a temperature in the range of 15°C to 30°C, which is typically 25°C.

The "erosion efficiency" of an electrode wire is equal to the ratio of the surface area cut in one minute to the average strength of the current passing through the electrode wire as it cuts the surface area. For example, for a 50 mm high steel part, if the feed rate of the wire to the material being cut is 2 mm/min, the processing speed is 100 mm ² /min. If the average processing current is 10 A, the erosion efficiency of the wire under these conditions is 10 mm ² /min/A.

Chapter II: Examples of Embodiments

Figure 1 shows an electrode wire 2 for electro-erosion processing as described in the introduction of this document.

For this purpose, the electrode wire 2 has a tensile strength in the range from 400 N/mm ² to 1,000 N/mm ² . The wire (2) extends along the longitudinal axis (4). In this case, the axis 4 is perpendicular to the plane of the sheet. The length of the wire 2 is greater than 1 m, typically greater than 10 m or 50 m.

The wire 2 has an outer surface 6 that is directly exposed to sparks during machining of parts by electro-erosion using this wire. The outer surface 6 is a cylindrical surface extending along the axis 4. The guide curve of face 6 is mainly a circle centered on axis 4. Therefore, the cross-section of the wire 2 is circular. The outer diameter D ₂ of the wire 2 typically ranges from 50 μm to 1 mm, most often from 70 μm to 400 μm. In this case, the diameter of the wire 2 is 250 μm.

In this embodiment, wire 2 is

- a central core (10) made of electrically conductive material; and

- Coating (12) deposited directly on the core (10)

Includes.

The function of the core 10 itself is to provide most of the tensile strength of the wire 2. A further function of the core is to provide electrical conductivity of the wire 2. For this, it is made of electrically conductive material. Typically, it is made of metal or metal alloy. For example, in this embodiment, core 10 is made of copper.

The diameter D ₁₀ of the core 10 ranges from 0.75 D ₂ to 0.98 D ₂ , typically from 0.85 D ₂ to 0.95 D ₂ , where D ₂ is the outer diameter of the electrode wire 2 . For example, in this case the diameter D ₁₀ is 230 μm.

The coating 12 is designed to increase the processing speed, thereby improving the erosion efficiency of the electrode wire and/or the quality of the surface of the part obtained after electro-erosion processing. The quality of the surface cut by electro-erosion is better the lower it exhibits roughness.

The thickness of the coating 12 is thin compared to the diameter D ₂ of the wire 2, i.e. less than 10% of the diameter D ₂ , preferably less than 8% of the diameter D ₂ . The thickness of the coating 12 corresponds, in cross section, to the shortest distance between the outer surface 6 and the circular border separating the core 10 from the coating 12 .

In this embodiment, coating 12 is

- two layers (14 and 16) stacked directly on top of each other in succession from the core (10) towards the outer face (6); and

- Possible surface layer 18 deposited directly on layer 16

is formed by

Below, the structure of the electrode wire 2 in the specific case where the layer 18 is present will be described. The entire description given for this particular case applies even if layer 18 is not present. In this case, the surface layer of the electrode wire 2 is directly layer 16 .

Layer 14 is a homogeneous and uniform layer made of copper-zinc beta phase alloy. Therefore, the zinc concentration in layer 14 typically ranges from 45 atomic percent to 50 atomic percent, with the remainder being copper and unavoidable impurities. The thickness of layer 14 is, for example, less than 5 μm.

Layer 16 is a homogeneous layer made of copper-zinc gamma phase alloy. The zinc concentration in layer 16 is high, ie in this case above the threshold S ₁₆ . This threshold S ₁₆ is greater than 65.4 atomic %, preferably 66.4 atomic %, 68.4 atomic %, or even greater than 70 atomic %, with the remainder being copper and unavoidable impurities. The zinc concentration in layer 16 is generally less than 84 atomic percent or 75 atomic percent.

According to a recently updated phase equilibrium diagram of the copper-zinc system, at steady state, the copper-zinc gamma phase alloy has a zinc concentration of 60 to 62 atomic percent at ambient temperature, with the remainder being copper. A recently updated phase equilibrium diagram of the copper-zinc system was published, for example, in the paper: Liang et al.,: "Thermodynamic assessment of the Al-Cu-Zn system, part I: Cu-Zn binary system ", CALPHAD, volume 51, 2015, pages 224 to 232.

Accordingly, when the zinc concentration is above the threshold S ₁₆ , the copper-zinc gamma phase alloy of layer 16 is not stable at ambient temperature. In this case, it is in a metastable state. In the metastable state, the transformation of the copper-zinc gamma phase alloy to its stable state, and therefore the decrease in its zinc concentration, is very slow at ambient temperature. In other words, this transformation of the gamma phase to its stable state at ambient temperature is practically undetectable by humans. Accordingly, the composition of this gamma phase in a metastable state, if this wire 2 is stored and transported under normal conditions and maintained at ambient temperature, from the time it was manufactured when it reaches the processing area of the electro-erosion machine. Little changes until. A method for producing a metastable layer of this copper-zinc alloy is described below.

The thickness of layer 16 exceeds the thickness of layer 18. 1 , by way of example, the thickness of layer 16 also exceeds the thickness of layer 14. Advantageously, the thickness of layer 16 exceeds 10%, 20% or 30% of the total thickness of coating 12. For this purpose, the thickness of layer 16 typically exceeds 1% or 2% of the diameter D ₂ . For example, the thickness of layer 16 is greater than 2.5 μm or 5 μm or 10 μm. The thickness of layer 16 is also so thin that it may crack upon drawing of the electrode wire. For this purpose, for example, the thickness of layer 16 is less than 25 μm or 20 μm.

Layer 16 is located less than 1 μm, preferably less than 0.5 μm, from the outer surface 6. In this case, it is separated from the outer face 6 only by a layer 18 . Therefore, for this purpose, the thickness of layer 18, if present, is less than 1 μm, preferably less than 0.5 μm.

Layer 18 is a more zinc-rich metal surface layer than layer 16. For example, layer 18 is made of a copper-zinc alloy having a zinc concentration that exceeds that of layer 16. Typically, the difference between the zinc concentration in layer 16 and the zinc concentration in layer 18 is greater than 2 atomic % or 5 atomic % or 10 atomic %. Typically, layer 18 is a copper-zinc epsilon phase or delta phase or eta phase alloy layer or is made of zinc.

In this embodiment, layers 16 and 18 are fractured. Accordingly, layers 16 and 18 contain cracks that, in cross section, divide each of these layers into several regions that are mechanically separated from each other by radial cracks. As explained below, such cracking is obtained by drawing a wire with uniform or substantially uniform layers 16 and 18. After drawing, the same material no longer extends completely continuously around the axis 4, but is divided in the cross section into several material regions, mechanically separated from each other by radial cracks. These cracks extend primarily radially and completely cross layers 16 and 18.

For example, a crack appears on the outer surface 6 starting at a circular boundary between layers 14 and 16.

Figure 1 schematically shows three cracks (22 to 24). These three cracks 22 to 24 divide layer 18 into three separate regions 26 to 28 and layer 16 into three separate regions 30 to 32.

These cracks correspond to hollow depressions or depressions in the solid or liquid material. The width of the crack in the direction perpendicular to the radial direction in which the crack extends is generally less than 2 μm. In this case, it should be emphasized that if the thickness of layer 18 is very thin, the copper-zinc alloy of layer 18 does not penetrate into the gaps and does not cover these gaps.

Each region of layer 16 is typically longer than the thickness of layer 16. In this case, each area of layer 16 is longer than 5 μm or 10 μm. In this document, in cross-section, the length and width of the regions are defined to be equal to the length and width, respectively, of the rectangle with the smallest surface area completely encompassing these regions.

Chapter II.1: Manufacturing Examples Using Fast Copper Diffusion:

Example 1: Rapid diffusion in a tunnel furnace

This first embodiment of the method for manufacturing the wire 2 is explained with reference to the flow chart in FIG. 2 . In this first embodiment, the threshold S ₁₆ is chosen to be 66.4 atomic percent and layer 18 is omitted.

During step 80, an initially rough metal wire is provided. In this embodiment, the coarse wire is a copper wire with a diameter of 1.25 mm.

Then, during step 82, fabrication is made on the coated wire. This coating continuously covers the entire outer surface of the rough wire. This coating is made of a material or materials capable of forming a layer 16 overlaid by a more zinc-rich layer when the temperature is in the range of 500° C. to 700° C. In this embodiment, the coating is formed, at this stage, solely with a zinc layer deposited directly on the outer side of the rough wire. For this purpose, a zinc layer is deposited on the coarse wire by means of an electrogalvanizing method to obtain an electrogalvanized wire with a diameter exceeding 1.25 mm.

In this case, after completion of step 82, this electrogalvanized wire is drawn until its diameter is 420 μm. At this stage, in this first embodiment, the thickness of the zinc coating is 25 μm in order to obtain a thick layer 16 which makes it easier to measure the zinc concentration.

During step 84, the electrogalvanized and drawn wire is heated to a temperature equal to T _c . The temperature T _c ranges from 500°C to 700°C. In this first production example, the temperature T _c ranges from 500°C to 600°C, even more advantageously from 559°C to 600°C. If a temperature T _c of 600° C. or lower is selected, the formation of zinc droplets that melt during heating is limited. In this case, the temperature T _c is 600°C.

For example, during step 84, an electrogalvanized and drawn wire is introduced into a heating zone having an internal temperature equal to T _c . Moreover, preferably, this heat treatment is carried out at atmospheric pressure in air in order to oxidize the outer surface of the electrode wire.

In this case, the electrogalvanized wire is considered to be formed by a series of successive sections of electrogalvanized wire arranged one after another along the axis 4, where each such section is very short. For example, in the description provided herein, a short portion is a portion having a length of 0.1 mm. Successive sections of the electrogalvanized wire one after another enter the heating zone, and these successive sections are in turn heated to a temperature T _c . More specifically, the heating zone includes an inlet and an outlet, between which the temperature is equal to the temperature T _c . The temperature before the inlet and after the outlet are 2 to 3 times lower than the temperature T _c . In this case, this heating zone is the tunnel of the tunnel furnace.

Each piece of electrogalvanized wire enters the heating zone through the inlet and then moves at a constant speed within the heating zone. Finally, these parts remain within the heating zone for a duration d ₀ and then exit the heating zone through the outlet. The duration d ₀ is

- The moment a part of the electrogalvanized wire enters the heating zone t _ini ; and

- the moment t ₀ at which this same portion of the electrogalvanized wire leaves the heating zone.

It is the same as the time interval separating .

The duration d ₀ is adjusted by setting the speed of movement of the electrogalvanized wire within the heating zone. The entire electrogalvanized wire passes through a heating zone such that upon completion of step 84 the entire zinc coating is heated to temperature T _c .

As taught in application US 5762726 A, at temperature T _c , copper slowly diffuses into the zinc coating. Therefore, in certain areas of the coating initially made of zinc, the copper concentration increases slowly over time.

Additionally, because copper diffuses within the coating as it progresses from the coarse copper wire toward the outside of the wire, a copper concentration gradient exists throughout the thickness of the coating. The copper concentration in the coating gradually decreases from the rough wire towards the outside. Conversely, the zinc concentration increases as the outer surface of the wire is approached. Due to this copper concentration gradient, during step 84, overlayers of several copper-zinc alloy layers of various phases appear. In this overlayer of copper-zinc alloy layers, the layers are arranged in such a way that the zinc concentration increases as the outer surface is approached. Therefore, the copper-zinc alloy surface layer is always the layer with the highest zinc concentration.

In this case, the goal of step 84 is to form a copper-zinc gamma phase alloy layer 16 located less than 1 μm from the outer surface 6 of the electrode wire and also exhibiting a high zinc concentration.

When the method described in application US 5762726 A is carried out, the zinc concentration of the copper-zinc gamma phase alloy layer is close to its maximum at the moment t _opt when the copper-zinc epsilon phase alloy layer overlying said layer disappears. was noticed. This is actually explained by the fact that the zinc concentration in the gamma phase tends to reach that of the epsilon phase as long as this epsilon phase exists. However, once the epsilon phase disappears, the zinc concentration of the gamma phase tends to balance that of the copper-zinc beta phase alloy layer that appears beneath the copper-zinc gamma phase alloy layer. Therefore, once the copper-zinc epsilon phase alloy layer disappears, the zinc concentration in the copper-zinc gamma phase alloy layer rapidly decreases. Therefore, the zinc concentration in the copper-zinc gamma phase alloy layer is optimal at an instant close to t _opt , the moment the copper-zinc epsilon phase alloy layer disappears. It should be noted that this teaching is absent from application US 5762726 A. In fact, this literature does not teach that it is advantageous to stop heating the electrogalvanized wire at the instant t _opt , or at an instant very close to the instant t _opt . In contrast, application US 5762726 A states that heating is stopped well before the instantaneous t _opt to obtain a copper-zinc epsilon phase alloy surface layer, or, conversely, well after the instantaneous t _opt to obtain a copper-zinc gamma phase alloy surface layer. It is urged to stop heating.

Consequently, in order to take advantage of this observation, in this case, for each portion of the electrogalvanized wire, step 84 is stopped at an instant t ₀ , which ranges from instants t _{0 min} to t _{0 max} . The moment t _0min is the moment when the thickness of the copper-zinc epsilon phase alloy surface layer overlying the copper-zinc gamma phase alloy layer becomes 1 μm. In fact, when the thickness of the copper-zinc epsilon phase alloy layer becomes less than 1 μm, the zinc concentration in the copper-zinc gamma phase alloy layer is at or very close to the maximum. Moreover, it is important that the thickness of the copper-zinc epsilon phase alloy layer is small to limit the deformation of the surface topography of the outer surface during electro-erosion. Moreover, it was noted that the erosion efficiency of the copper-zinc epsilon phase alloy was lower than that of the copper-zinc gamma phase alloy.

The moment t _0max occurs after the moment t _opt when the copper-zinc epsilon phase alloy surface layer disappears. After the moment t _opt , a layer of copper-zinc gamma phase alloy forms the surface layer of the electrode wire in this manufacturing step. After the instant t _opt , the zinc concentration in the copper-zinc gamma phase alloy layer rapidly decreases and falls below the critical value S ₁₆ at the instant t _0max . Typically, the moment t _0max is in the interval [t _ini ; t _0max ] is the moment such that the duration d _0max is less than 1.2*d _opt or 1.1*d _opt , where the duration d _opt is the interval [t _ini ; It is the same as the duration of t _opt ].

Therefore, for each section of electrogalvanized wire, the interval [t _{0 min} ; By choosing an instant t ₀ that falls within [t _{0 max} ], a layer of copper-zinc gamma phase alloy forms the surface layer of the electrode wire or just a very thin surface layer that is more zinc-rich, i.e. in this case copper-zinc epsilon. At the moment the zinc concentration of the copper-zinc gamma phase alloy layer, which is covered by a very thin layer of phase alloy, exceeds S ₁₆ , step 84 is stopped.

Typically, the duration d ₀ , and therefore the moment t ₀ , is determined by successive experiments. In fact, as stated in Chapter I:

1) It allows measuring the thickness of the copper-zinc gamma phase and epsilon phase alloy layers in the cross section of the electrode wire;

2) which allows determining the zinc concentration of the copper-zinc gamma phase alloy layer

There is a way.

Accordingly, the duration d ₀ can be determined by successively trying several possible values for this duration d ₀ .

Afterwards, the moment t ₀ is divided into the interval [t _opt ; t _0max ], so layer 18 is omitted.

By way of example, it was noted that under these conditions, a duration d ₀ of 10 seconds allowed to obtain a copper-zinc gamma phase alloy surface layer with a zinc concentration of 67 atomic percent.

After the end of the duration d ₀ , the coating deposited on the rough copper wire consists of a copper-zinc beta phase alloy layer (14) overlaid by a copper-zinc gamma phase alloy surface layer (16).

At this stage, this rapid heating of the electrogalvanized wire can be achieved, for example, by placing a coil of electrogalvanized wire with several thousand turns in a conventional static furnace heated to a temperature T _c . It should be noted that there is no Static furnaces are furnaces containing electrogalvanized wires that do not move throughout the heating period. Indeed, in this case, the heating rate of a turn of the electrode wire that is mechanically isolated from the air heated to temperature T _c by the other turns overlaid is much slower than the heating rate of a turn in direct contact with the heated air. Therefore, if the coil is placed in air heated to temperature T _c for 10 seconds, only a small portion of the electrogalvanized wire heats up rapidly, while another portion of the electrogalvanized wire heats much more slowly. As a result, while only a portion of the electrogalvanized wire contains the copper-zinc gamma phase alloy layer characteristic of layer 16, a significant portion of the more slowly heated electrogalvanized wire contains these copper alloys with high zinc concentrations. -Does not contain zinc gamma phase alloy layer. In other words, it is impossible to precisely control the duration d ₀ for each section of electrogalvanized wire using conventional static furnaces.

For each section of electrogalvanized wire, a rapid cooling step 90 is carried out as soon as the instant t ₀ is reached, i.e., in this case, from the end of the duration d ₀ . The purpose of the cooling step 90 is to fix the composition of the layer 16 obtained at the instant t ₀ and render it metastable at ambient temperature. For this purpose, immediately after the instant t ₀ , during step 90, each portion of the wire is subjected to rapid cooling for a duration d ₁ , whereby the temperature of the layer 16 of this portion is reduced to 30° C. in less than 10 seconds. falls suddenly.

This cooling is referred to as rapid cooling because the duration d ₁ is less than 10 seconds. Preferably, the duration d ₁ is less than 1 second or 0.5 seconds. To obtain this short duration d ₁ , the cooling rate during step 90 is fast. In this first embodiment, the duration d ₁ is less than or equal to 1 second. Therefore, the average cooling rate during the duration d ₁ is more than (T _c -30)°/s. Therefore, in this first manufacturing example, the average cooling rate is greater than 570° C./s.

In this case, step 90 is applied sequentially to each portion of the wire exiting the heating zone, such that each portion of the wire undergoes this rapid cooling. Therefore, the zinc concentration of layer 16 is thereby fixed over the entire length of electrode wire 2.

For this purpose, as soon as a section of wire leaves the heating zone, it is immersed in a fluid at ambient temperature. For example, in this case, a liquid bath at 25°C is installed at the outlet of the heating zone. For example, the liquid is water. In this case, each portion of the wire passes an initial section of its path between the outlet of the heating zone and the inlet of the bath, during which such portion is first exposed to air at ambient temperature. This portion of the wire then enters an ambient temperature bath and is in direct contact with the ambient temperature liquid while passing through the second section of this bath. After the end of the second section, part of the wire leaves the bath. The lengths of the first and second zones are such that the temperature of each portion of the wire is such that after instant t ₀ It is adjusted to drop below 30°C in less than 10 seconds. In this case, each portion of the wire passes through the first zone in less than one second. The average cooling rate of a section of wire in water at ambient temperature is approximately 20,000°C/s. Under these conditions, in this first manufacturing example, the duration d ₁ is 1 second or less.

At this stage, it should be noted that such rapid cooling cannot be achieved by, for example, immersing a coil of electrode wire with thousands of turns, heated to temperature T _c , in a bath at ambient temperature, or even in a bath of liquid. Indeed, in this case, for reasons similar to those disclosed in the case of rapid heating, the cooling rate of turns of the electrode wire that are mechanically isolated from the liquid by other overlaid turns is much slower than the cooling rate of turns in direct contact with the liquid. In other words, it is not possible to precisely control the duration d ₁ for cooling of each part of the electrode wire by immersing the coil with the turns in a liquid bath.

After the end of step 90, layer 16 is in a metastable state, as long as the wire is maintained at ambient temperature, at which its zinc concentration exceeds the threshold S ₁₆ .

Next, during step 94, the wire obtained at the completion of step 90 is drawn to obtain the electrode wire 2. This drawing step 94 allows the diameter of the electrode wire to reach the desired diameter, in this case a diameter of 250 μm. Step 94 causes layers 16 and 18 to crack. Accordingly, during this step 94, most of the cracks located in layers 16 and 18 are created.

Figure 3 is an image of a portion of a cross-section of the electrode wire 2 obtained after the end of step 90 and before the drawing step 94. These images were obtained using an optical microscope. The composition of layer 16 was measured using an energy-dispersive spectroscopy (EDS) spectroscopic probe. The zinc concentration of layer 16 is 67 atomic%.

Figure 4 is an image of a portion of the electrode wire 2 obtained upon completion of the drawing step 94. These images were also obtained using an optical microscope. Layer 16 is cracked. It is therefore divided into a number of regions separated from each other by fissures. These images show that part of the copper-zinc gamma phase alloy region can be separated from the outer surface 6 by another region of copper-zinc gamma phase alloy. In this case, these areas are located more than 1 μm from the outer face 6. However, the majority of the copper-zinc gamma phase alloy area, typically more than 70% or 80%, is located less than 1 μm, in this case less than 0.5 μm, from the outer surface 6. In this document, “majority” of the copper-zinc gamma phase alloy area corresponds to more than 50% of the copper-zinc gamma phase alloy area present in the electrode wire.

This image also shows that some of these areas may be covered by the remaining portion 100 of layer 18.

Example 2: Joule effect heating

The second manufacturing example is

- the thickness of zinc is 18 μm;

- heating is carried out by Joule effect;

- the duration d ₀ is selected such that the moment t ₀ is in the range from t _{0 min} to t _opt so that the layer 18 is present in the produced electrode wire.

Except for, it is the same as the first embodiment.

In the case of Joule effect heating, the heating zone is a segment of electrogalvanized wire positioned between a first and second conductive pulley polarized by a direct current generator. The potential difference between these two pulleys creates a direct current that flows in the segment of electrogalvanized wire located between these two pulleys. Therefore, the segment of electrogalvanized wire located between the two pulleys is heated by the Joule effect. Typically, the strength of direct current is greater than 10 A.

The various parameters of Joule effect heating are such that the moment each section of electrogalvanized wire leaves this heating zone t ₀ is in the interval defined above [t _{0 min} ; It is adjusted to fall within [t _0max ]. The adjustable parameters of Joule effect heating are, inter alia, the intensity of the direct current, the potential difference between the two pulleys, the unwinding speed of the electrogalvanized wire and the length of the heating zone of the electrogalvanized wire between the two pulleys. For example, in this case, the length of the heating zone before the electrogalvanized wire enters directly into the 25°C water bath is considered to be 1,530 mm. The unwinding speed of the electrogalvanized wire in the heating zone is 4.59 m/min. The intensity of the current flowing in the electrogalvanized wire between the two conductive pulleys is 17.9 A. In these conditions, the duration d ₀ is 20 seconds. In this embodiment, each portion of electrogalvanized wire may enter the bath before reaching the second pulley, so there is no air exposure prior to bath immersion.

The wire obtained after step 90 was analyzed. In certain areas around the wire, layer 16 is covered with a more zinc-rich layer of copper-zinc alloy, while in other areas, on the contrary, layer 16 is the only metal alloy present on the surface of the wire. am. In both cases, zinc oxide is also present on the surface of the wire.

In the regions covered by the more zinc-rich layer, layer 16 essentially has a zinc concentration ranging from 65.4 atomic % to 69.4 atomic %. In areas where layer 16 is not covered by a more zinc-rich layer, the zinc concentration of layer 16 essentially ranges from 65.4 atomic % to 66.3 atomic %.

The more zinc-rich layers, where they exist, will appear to be made of copper-zinc delta phase alloy.

Example 3: 700°C diffusion temperature

When the temperature T _c is above 400℃, the section [t _0min ; The following experiment was performed to show that t _0max ] is very short. This shows that it is not possible to produce a copper-zinc alloy layer with a high zinc concentration simply by practicing the teachings of application US 5762726 A.

A 420 μm diameter and 100 mm long copper wire coated with 18 μm zinc was placed in a static furnace for a specified duration at a temperature of 700°C, then it was quickly removed from the furnace within less than 1 second and placed in water at ambient temperature. It was immersed.

A residence time d ₀ of 6 seconds in the static furnace gave a copper-zinc gamma phase alloy layer with a zinc concentration of 68 atomic percent, overlaid by a copper-zinc epsilon phase alloy layer 18 with a thickness of less than 0.5 μm. It allows you to do it. The electrode wire obtained under the same conditions and for a residence time of 7 seconds in a static furnace does not contain the copper-zinc epsilon phase alloy surface layer 18 and the zinc concentration of the copper-zinc gamma phase alloy surface layer is only 63 atomic%.

This observation was also confirmed by running the method of Example 1, but in this case

- The coarse wire is a brass wire with a zinc concentration of 37 atomic percent;

- During step 82, the wire is drawn to a diameter of 460 μm, after drawing the thickness of the zinc coating is only 5 μm;

- The duration d ₀ is 9 seconds.

Under these conditions, the zinc concentration of the resulting surface layer 16 is 63 atomic%, which is much less than 65.4 atomic%. In fact, because the thickness of the zinc coating decreases, t _opt occurs earlier, at the moment the copper-zinc epsilon phase alloy layer disappears. As a result, by stopping step 84 after 9 seconds, the rapid cooling step 90 is too late, after the instant t _0max . Occurs.

Chapter II.2: Manufacturing Examples by Slow Copper Diffusion:

Example 4:

The present manufacturing method, during step 84,

- the thickness of zinc is 18 μm;

- A static furnace is used;

- the temperature T _c is 250°C;

- The duration d ₀ is 65 minutes,

- During step 90, the cooling is not rapid cooling.

Except for this, the manufacturing method is the same as in Example 1.

In this embodiment, because the temperature T _c is low, i.e. typically below 300° C., the electrogalvanized wire applied to the electrogalvanized wire even if the heated electrogalvanized wire is in the form of a coil containing thousands of turns. The duration d ₀ is long enough so that the heat treatment is substantially the same in all parts of this electrogalvanized wire.

During the cooling step 90, at the exit of the heating zone, the wire is exposed to ambient air at only 25° C., without the need to perform rapid cooling. In fact, tests have shown that for low temperatures T _c such rapid cooling of the wire after it leaves the static furnace is not necessary. In other words, the zinc concentration in layer 16 is the same with and without rapid cooling.

Upon completion of step 94, the resulting wire comprises a layer 18 having a thickness of less than 0.5 μm. This layer 18 is a copper-zinc epsilon phase alloy. Layer 16 has a zinc concentration ranging from 65.3 atomic percent to 68.3 atomic percent. The copper-zinc gamma phase alloy of this layer 16 appears to be less ductile than a layer of similar composition obtained at 600°C.

Chapter II.3: Manufacturing using electroplating

Example 5:

Fabrication using electroplating involves depositing layer 16 directly via water phase electroplating without undergoing a copper diffusion step.

For this purpose, a coarse wire forms the cathode and an anode containing a mixture of copper and zinc is used, the zinc concentration of the anode being greater than 65.4 or 77 atomic percent. For example, for the tests described herein, the anode is formed from a mixture of copper balls and zinc plates. The electrolytic bath is adapted to deposit a copper-zinc gamma phase alloy layer on a coarse wire with a high zinc concentration.

In this embodiment, Joe

- Water as solvent;

- Sodium hydroxide (beads) 12 kg NaOH, i.e. 60 g/l;

- 12 kg of sodium cyanide NaCN, i.e. 60 g/l;

- 3.4 kg of copper cyanide CuCN, i.e. 17 g/l;

- 12 kg of zinc cyanide Zn(CN) ₂ , i.e. 60 g/l; and

- 80 g of sodium sulfite Na ₂ SO ₃ , i.e. 0.4 g/l

It is a tank of the "Oplinger" type with a capacity of 200 liters.

The temperature of the bath is 45℃. The current density is 20 amperes per square decimeter (20 A/dm ² ). Faraday efficiency is approximately 56%. Therefore, a coarse brass wire with a diameter of 0.51 mm was coated with a 7 μm thick layer (16).

The zinc concentration measured by EDS analysis of this layer 16 is 66.4 atomic percent.

The wire coated with this electroplated gamma phase is then drawn to obtain a diameter of 0.25 mm.

The advantage of electroplating a copper-zinc alloy is that its composition is constant throughout the thickness of the coating, unlike diffusing the zinc onto a copper or brass substrate, which has a compositional gradient. Accordingly, the electrode wire manufactured according to this Example 5 does not include layer 14 or layer 18, but only layer 16.

Example 6:

The manufacturing method of Example 6 is the same as that of Example 5, except that the bath is modified to increase the zinc concentration in layer 16. For this purpose, instead of the bath of Example 5, a bath having the following characteristics is used:

- The solvent is water;

- The concentration of sodium hydroxide (NaOH) is 90 g/l;

- The concentration of sodium cyanide (NaCN) is 60 g/l;

- The concentration of copper cyanide (CuCn) is 17 g/l;

- the concentration of zinc cyanide (Zn(CN) ₂ ) is 90 g/l;

- The concentration of sodium sulfite (Na ₂ SO ₃ ) is 0.6 g/l.

The zinc concentration of layer 16 measured by EDS analysis under the same electroplating conditions is 82.3 atomic%.

When this wire was drawn to a diameter of 0.25 mm, cracking of the coating was observed, which is characteristic of copper-zinc gamma phase alloys rather than copper-zinc epsilon phase alloys.

However, if the coating obtained using the above bath also exhibits copper-zinc epsilon phase alloy residues, these residues can be reduced or eliminated by reducing the concentrations of NaOH and Zn(CN) ₂ . At that time, for example, the concentrations of NaOH and Zn(CN) ₂ range from 60 g/l to 90 g/l.

Chapter II.4: Performance

The erosion efficiencies of various 0.25 mm diameter wires are compared. Each test was performed under the following conditions:

- The electro-erosion machine used is a machine manufactured by GFMS (GF Machining Solutions) (reference number: “CUT 200 MS”);

- The cutting parts are steel blocks 50 mm high;

- the injection nozzle is separated from the part by approximately 5 mm at the top and bottom;

- The processing parameters are those of a standard bare brass wire with a diameter of 0.25 mm and a tensile strength of 900 N/mm ² , under the conditions for a plated injection nozzle.

To avoid breakage of the wire (the nozzle is effectively separated) and to measure the erosion efficiency to clearly demonstrate the effectiveness of layer 16, the spark frequency was lowered to a 25 μs interval between the two sparks, which is approximately 6.5 A. corresponds to the average intensity of The frequency was then increased by decreasing the time interval between the two sparks to determine the maximum cutting speed of the tested wire before it broke.

The compared electrode wires are:

- Wire A: This is the wire sold by ThermoCompact® under the trademark "Thermo SA" and described in application EP 1949995; It is a wire with a brass core (64% copper and 36% zinc by mass) and a surface layer of copper-zinc gamma phase alloy layers divided into blocks. The zinc concentration of this block in the gamma phase is 61.3 atomic percent;

- Wire B: This is a wire with a zinc concentration of 66.4 at% in the surface layer 16, manufactured according to Example 5 described above;

- Wire C: This is a wire with a zinc concentration of 82.3 atomic percent in layer 16, manufactured according to Example 6 described above.

Wire B has better erosion efficiency than wire A. Wire C withstands greater machining force before breaking. Therefore it can reach a higher maximum processing speed than other wires.

It should be noted that wire A has an oxide layer about 50 nm thick, which is advantageous for its erosion efficiency. Wires B and C have much thinner oxide layers. It is assumed that if the manufacturing conditions for wire B are changed to obtain an oxide thickness of approximately 50 nm thick, its erosion efficiency will be even higher.

Chapter III: Alternative Embodiments

Alternative Embodiments of Electrode Wires:

The core of the electrode wire does not necessarily have to be made of copper or an alloy containing copper, such as brass, for example. For example, the core may be made of steel or another electrically conductive metal. If the core does not contain copper, layer 16 is obtained by electroplating.

The core does not necessarily have to be made of a single metal or single metal alloy. In an alternative embodiment, the core includes several layers each made of a respective metal or metal alloy. For example, the core includes a central body made of steel or copper coated with a layer of brass. This brass layer may be a copper-zinc beta phase alloy layer.

Layer 14 may be omitted. This is particularly the case if layer 16 is produced by electroplating.

In an alternative embodiment, layer 16 is uniform and does not crack. Layer 16 is therefore formed by a single region extending continuously throughout the perimeter of core 10. For example, to manufacture this alternative embodiment, during step 82, the electrogalvanized wire is drawn to directly obtain the desired final diameter and the drawing step 94 is omitted. For example, other steps of the method of Figure 2 remain the same.

In an alternative embodiment, layer 18 is a copper-zinc delta phase or eta phase alloy or is made of zinc.

In an alternative embodiment, layer 18 is not present, so layer 16 forms the surface layer of the electrode wire.

Alternative Embodiments of Manufacturing Method:

Numerous different methods for manufacturing the wire 2 are possible. For example, fabrication methods involving fast or slow copper diffusion described in Chapter II can be performed using coarse wires that are not necessarily made entirely of copper. For example, in an alternative embodiment, the coarse wire includes only a surface layer having a copper concentration greater than 50 or 60 atomic percent and less than 95 or 90 atomic percent. Likewise, it can be implemented using coatings with zinc concentrations of less than 100 atomic percent. However, preferably the zinc concentration of the coating is high, i.e. greater than 95 atomic percent or 98 atomic percent.

The temperature T _c for carrying out the production method by slow copper diffusion can be selected from 150°C to 500°C. Therefore the duration d ₀ must be adjusted depending on the selected temperature T _c . However, preferably, the temperature T _c is chosen to be below 300°C or 250°C or 200°C, so that a static furnace can be used and to avoid carrying out rapid cooling. In cases where the temperature T _c exceeds 300°C or 400°C, a tunnel furnace is used instead of a static furnace to better control the durations d ₀ and d ₁ . In this case, the method of preparation by slow copper diffusion is identical to that of Example 1, except that the temperature T _c is in the range of 150° C. to 500° C. and not 500° C. to 700° C.

The drawing step 94 may be omitted.

Chapter IV: Advantages of the Described Embodiments:

Electrode wires with a high zinc concentration and wherein the copper-zinc gamma phase alloy region is less than 1 μm from the outer surface of the electrode wire have at least one of the following advantages compared to the electrode wire of application US 5945010 A:

- Erosion efficiency is improved and/or

- Maximum erosion speed is improved.

Herein, the fact that the performance of the electrode wire described in this document has been improved is explained as follows. Because the gamma phase layer 16 has a high zinc concentration, its melting point is high and its sublimation temperature is low. These are two features recognized as improving the performance of electrode wires. Performance is also improved by the fact that the thickness of the more zinc-rich surface layer is less than 0 or 1 μm. In fact, the melting point of layer 18 is lower than that of layer 16. Accordingly, during electro-erosion, this layer 18 melts before the copper-zinc gamma phase alloy. Reducing the thickness or removing this surface layer 18 significantly reduces the amount of liquid that appears on the surface of the electrode wire during the electro-erosion process. As a result, craters caused by, for example, electro-erosive sparks have less re-solidification area. Additionally, the electrode wire loses less material during sparking. Moreover, fewer cracks or pores are concealed by the flow of molten metal. Therefore, the surface shape of the electrode wire surface is better preserved. therefore,

- Reducing the consumption of electrode wire by reducing the unwinding speed of the electrode wire while maintaining excellent processing speed, or

- Increasing processing speed while maintaining unwinding speed

This is possible.

It should be noted here that in application US 5945010 A, the copper-zinc gamma phase alloy layer of specimen no. 4 has a lower zinc concentration than that of specimen no. 3. However, application US 5945010 A teaches that specimen number 4 has the best performance. Moreover, application US 5945010 A does not teach a method of further increasing the zinc concentration of the surface layer of specimen no. 4. In particular, this application does not teach that the heating of the electrode wire should be stopped rapidly at an instant close to the instant t _opt .

By the fact that each region of the copper-zinc gamma phase alloy is directly coplanar with the outer surface, the amount of liquid that appears during electro-erosion is further reduced. This further improves the performance of the electrode wire.

By further increasing the zinc concentration in each region of the copper-zinc gamma phase alloy, especially making the zinc concentration greater than 68.4 atomic percent, the performance of the electrode wire can be further improved.

Due to the fact that the copper-zinc alloy layer is cracked, the erosion efficiency of the electrode wire can be increased.

Diffusion heat treatment above 500° C. makes it possible to obtain an electrode wire further comprising a layer 14 below the layer 16, which is advantageous.

In contrast, if the electrode wire is manufactured using slow copper diffusion, a thick layer 14 beneath the layer 16 cannot be obtained. However, due to the slow diffusion, layer 16 can be obtained with a more uniform thickness.

Rapid cooling of layer 16 limits or prevents its zinc concentration from decreasing during step 90.

Deposition of the layer 16 by electroplating makes it possible to obtain a layer 16 with a zinc concentration of more than 66 or 70 atomic percent. Additionally, the thickness of layer 16 is more uniform.

Claims (15)

An electrode wire that can be used as an electrode wire for electro-erosion processing,
The electrode wire is
- a metal core (10) extending along a longitudinal axis; and
- a coating on said metal core comprising one or more copper-zinc gamma phase alloy regions (30-32), each of which is formed solely of copper-zinc gamma phase alloy, and which copper-zinc gamma phase alloy at an ambient temperature of 25° C. A coating wherein the zinc concentration within each of the gamma phase alloy regions is greater than 65.4 atomic percent.
Including,
Characterized in that more than 50% of the copper-zinc gamma phase alloy region (30-32) is located less than 1 μm from the outer surface of the electrode wire.
electrode wire. 2. The electrode wire of claim 1, wherein at ambient temperature, more than 50% of the copper-zinc gamma phase alloy regions (30-32) are directly coplanar with the outer surface of the electrode wire. 3. The electrode wire of claim 1 or 2, wherein at ambient temperature, the zinc concentration in each of the copper-zinc gamma phase alloy regions (30-32) is at least 68.4 atomic percent. 4. The method of claim 1 or 3, wherein at ambient temperature the coating is continuously applied from the outside towards the metal core of the electrode wire.
- a first surface layer (18) with a zinc concentration of more than 72 at% and a thickness of less than 1 μm or 0.5 μm; and just below the surface layer
- a second layer (16) containing the respective copper-zinc gamma phase alloy regions (30-32)
An electrode wire comprising a. 5. Electrode wire according to claim 4, wherein the surface layer (18) is made of copper-zinc epsilon phase alloy. Electrode wire according to claims 4 or 5, wherein the coating comprises, immediately beneath the second layer (16), a third copper-zinc alloy homogeneous layer (14) formed solely of the copper-zinc beta phase alloy. 7. Electrode wire according to any one of claims 1 to 6, wherein the electrode wire comprises cracks (22-24) mechanically separating the various copper-zinc gamma phase alloy regions in a cross-section of the electrode wire. . 8. The method according to any one of claims 1 to 7, wherein the thickness of at least one of the copper-zinc gamma phase alloy regions (30-32) in the direction perpendicular to the longitudinal axis exceeds 1% of the outer diameter of the electrode wire. phosphorus electrode wire. 9. The method of any preceding claim, wherein more than 50% of the copper-zinc gamma phase alloy regions (30-32) have a length greater than 5 μm and a width greater than 4 μm, perpendicular to the longitudinal axis. An electrode wire having a cross-section, wherein the length and width of the cross-section of the copper-zinc gamma phase alloy region are respectively equal to the width and length of a rectangle having the smallest surface area completely encompassing the cross-section. A method of manufacturing an electrode wire as claimed in any one of claims 1 to 9, said method comprising manufacturing a copper-zinc gamma phase alloy layer on a metal core, said layer being heated at 25° C. At an ambient temperature of
- located less than 1 μm from the outer surface of the electrode wire,
- The zinc concentration exceeds the threshold S ₁₆ , wherein the threshold S ₁₆ is equal to or greater than 65.4 atomic%.
A method characterized by . 11. The method of claim 10, wherein preparing the copper-zinc gamma phase alloy layer comprises the following steps:
a) preparing a coating (82) on a rough metal wire comprising a surface layer having a copper concentration of more than 50 or 60 at%, wherein the coating is released from the surface layer of the rough wire when heated above 150° C. allowing diffusion of copper into the coating to form a copper-zinc gamma phase alloy layer; and then
b) heating each successive section of the rough wire on which the coating has been prepared in turn at a temperature T _c exceeding 150° C., so that in the heated section part of the coating is coated with a copper-rich overlay by a more zinc-rich surface layer. Step 84 of conversion into a zinc gamma phase alloy layer, for which each portion of the rough wire enters the heating zone at an instant t _ini and exits the heating zone at an instant t 0, wherein each portion of the rough wire enters the heating zone at an instant t ₀ and The unwinding speed of the wire is constant, and the moment t ₀ is
- the moment when the thickness of the more zinc-rich surface layer of the part of the rough wire exiting the heating zone is less than 1 μm or disappears; and
- the moment when the zinc concentration of the copper-zinc gamma phase alloy layer of the part of the coarse wire exiting the heating zone is still greater than 65.4 atomic%.
A step determined to correspond to; next
c) cooling (90) from instant t ₀ to the copper-zinc gamma phase alloy layer of the portion of the coarse wire that exits the heating zone at said instant t ₀ , dropping its temperature to 30° C. in less than 10 seconds, At this time, the cooling step is applied to each portion of the coarse wire exiting the heating zone. 12. The method according to claim 11, wherein during step b) each portion of the coating is brought to a temperature T _c in the range from 500° C. to 700° C. 13. The process according to any one of claims 10 to 12, wherein producing the coating comprises forming a layer with a zinc concentration of more than 98 at% on a surface layer of the coarse wire with a copper concentration of more than 50 or 60 at%. A method comprising direct manufacturing. 11. The method of claim 10, wherein preparing the copper-zinc gamma phase alloy layer comprises the following steps:
a) preparing a coating (82) on a rough metal wire comprising a surface layer having a copper concentration of more than 50 or 60 at%, wherein the coating is released from the surface layer of the rough wire when heated above 150° C. allowing diffusion of copper into the coating to form a copper-zinc gamma phase alloy layer; next
b) The coarse wire on which the coating has been prepared is heated in a static furnace at a temperature T _c in the range from 150° C. to 300° C., so that a portion of the coating is overlaid by a more zinc-rich surface layer, a layer of copper-zinc gamma phase alloy. wherein the thickness of the more zinc-rich surface layer gradually decreases as heating continues; next
c) stopping step b) at instant t ₀ to allow the temperature of the electrode wire to fall below 30°C again, where instant t ₀ is
- the moment the thickness of the more zinc-rich surface layer present on the rough wire is less than 1 μm or disappears; and
- the moment the zinc concentration of the copper-zinc gamma phase alloy layer on the rough wire is still greater than 65.4 atomic%.
A step corresponding to . 11. The method of claim 10, wherein making the copper-zinc alloy layer includes electroplating a copper-zinc gamma phase alloy layer on a metal core, wherein the layer has a zinc concentration of at least 65.4 atomic percent.

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