WO2024200375A1 - Precision resistive alloy based on copper, manganese, nickel and tin - Google Patents

Abstract

The invention relates to a precision resistive alloy based on copper (Cu) for producing a precision resistor, the alloy being characterised in that it consists of, in wt%: - manganese (Mn) in an amount of between 20.0 and 23.0%; - nickel (Ni) in an amount of between 4.5 and 8.0%; - tin (Sn) in an amount of between 0.2 and 2.0%; - optionally silicon (Si) in an amount of between 0.02 and 0.15%, in accordance with Sn+4*Si<2.0%, the remainder being copper and unavoidable impurities, and in which alloy the ratio (in wt%) of the amount of Mn to the amount of Ni is between 3.0 and 5.0. The alloy of the invention could, in particular, be used in the production of precision resistors, or in battery measurement and control systems, in shunts or in strain gauges.

Description

Description

Title of the invention: Precision resistive alloy based on copper, manganese, nickel and tin

[0001] The present invention relates to the field of precision resistive alloys based on copper and, more particularly, to a resistive alloy whose main constituents are copper and manganese, and also comprising nickel, tin, and optionally silicon.

[0002] Copper-manganese alloys are known for their electrical properties, and in particular for their resistivity.

[0003] In so-called "precision" resistive alloys, in addition to resistivity as an essential characteristic, there is the temperature coefficient of resistance, also noted TCR (Temperature Coefficient Resistance), as well as the thermoelectric power, noted PTE.

[0004] The present invention relates more specifically to an alloy having optimum stability of resistivity after exposure to temperature over a long period of use (several hundred hours), a very low temperature coefficient and a very low thermoelectric power, which will be used in precision resistors for current measurement or in standard resistors.

[0005] Thus, such an alloy will find an application in particular in the manufacture of precision resistors such as shunts (or micro-shunts) which are in particular essential in the control system of accumulator batteries (or BMS - Battery Management System) where the temperature has a major effect on the charging capacity of the battery, or even its destruction.

[0006] This alloy can also be used in the manufacture of precision chip resistors (or SMD - Surface Mount Resistor and Chip Resistors) such as metal foil resistors or current sense resistors (Current Sense Resistors).

[0007] Finally, this alloy will also find an application in the manufacture of strain gauges for which the measurements require high precision and temperature stability. [0008] The shunt, in particular, consists of a core made from a resistive alloy, and two copper connectors, and said connectors are assembled to the core by welding, the potential difference between the materials of the core and the copper connectors conditioning the PTE, the latter having to be as low as possible.

[0009] In other words, thermoelectric power reflects the appearance of a difference in electrical potential between a pair of materials subjected to a temperature gradient.

[0010] In the intended applications, namely precision resistors, the lowest possible PTE is sought, in order to avoid the existence of harmful parasitic current for certain applications, with, in parallel, a high resistivity value.

[0011] Resistivity, noted Q, as opposed to conductivity, defines the capacity of a material to block the passage of electrical charges, and therefore of current.

[0012] The resistivity Q of copper is very low (1.724 pQ.cm in the annealed state), which makes it an excellent electrical conductor. Indeed, the electrical conductivity of copper is defined as being equal to 100% IACS (International Annealed Copper Standard).

[0013] Finally, the temperature coefficient, TC, represents the variation of a physical property, which can be, for example, the thermal conductivity of a material, the mechanical strength, or the resistance of a conductor, as a function of temperature.

[0014] In the applications of the present invention, the physical quantity of interest is the temperature coefficient of resistance (TCR); it is therefore this property which will be measured, and for which we seek to achieve the lowest possible value.

[0015] In alloys whose main constituent is copper, manganese may be added to this copper, which has the effect of increasing the resistivity of the alloy and the thermoelectric power, while lowering the temperature coefficient.

[0016] The addition of nickel to the preceding alloy has the effects, on the one hand, of increasing the resistivity, with however a lesser effect than that of manganese and, on the other hand, of lowering the thermoelectric power. [0017] The TCR can be negative, positive or zero depending on the combination of elements and the temperature range.

[0018] Tin and silicon may also be added, in proportions of up to 3% by mass for tin, and 1% for silicon, to adjust the temperature coefficient of resistance, the thermoelectric power, and improve the temperature stability of the resistivity.

[0019] We thus know, in particular, from the American patent application published under number US 2020/224293, a resistance element manufactured from an alloy comprising copper, manganese in a proportion of between 23 and 28%, nickel in a proportion of between 9 and 13%, and tin, with a proportion of up to 1%.

[0020] Silicon may also be added, in a proportion of up to 1%.

[0021] This gives an alloy which gives the final product an interesting resistivity of around 90 pQ.cm.

[0022] However, precision resistive alloys containing a high proportion of manganese have disadvantages.

[0023] In particular, such alloys require, at the time of their preparation, the carrying out of a vacuum or controlled atmosphere fusion of the elements, so as to avoid the formation of MnO oxides likely to alter the properties of the alloy. In addition to the fusion, the transfer of the liquid alloy to the ingot mold frequently requires the use of technologies that do not involve passage to air (source process).

[0024] However, the implementation of a vacuum melting and casting step requires the use of specific equipment (vacuum enclosure, atmosphere control) which has the disadvantage of being expensive.

[0025] Furthermore, the stability of the temperature coefficient TCR and the thermoelectric power PTE still needs to be improved, in order to propose an alloy of optimal composition for the manufacture of precision resistors.

[0026] Other alloys are known in the state of the art, in particular compositions comprising between 6 and 10% manganese, and 3 to 9% aluminum, for applications in the manufacture of resistors. [0027] That being said, for such alloys, the resistivity values obtained are relatively low and of little interest for the intended applications, typically between 25 pQ.cm and 55 pQ.cm.

[0028] The same applies to CuMnSn alloys, for which the composition comprises between 5 and 12% manganese and 1 to 7% tin, and by means of which the resistivity values are centred around 30 pQ.cm.

[0029] The present invention aims to be able to propose a copper-based alloy, the composition of which is furthermore constituted by at least manganese, nickel and tin, for the production of precision resistors having both a high resistivity, of at least 70 pQ.cm, a low PTE and an optimal TCR in a temperature range from 20 to 50°C, while also exhibiting stability over time of their resistivity.

[0030] For this purpose, the invention relates to a precision resistive alloy based on copper (Cu) for the manufacture of a precision resistor, characterized in that said alloy consists of, in % by mass:

[0031] - manganese (Mn) in a proportion of between 20.0 and 23.0%,

[0032] - nickel (Ni) in a proportion of between 4.5 and 8.0%,

[0033] - tin (Sn) in a proportion of between 0.2 and 2.0%,

[0034] - Optionally silicon (Si) in a proportion of between 0.02 and 0.15%, then respecting Sn+4*Si<2.0%,

[0035] The remainder being copper and unavoidable impurities,

[0036] And in which alloy the ratio (in % by mass) between the proportion of Mn and Ni is between 3.0 and 5.0.

[0037] According to particular embodiments of the precision resistive alloy of the invention:

[0038] - the proportion of Sn within the alloy is between 0.6 and 1.6% by mass;

[0039] - the proportion of Mn within the alloy is between 20.0 and 22.0% by mass;

[0040] - the proportion of Ni within the alloy is between 5.0 and 6.5% by mass; [0041] - said alloy has the following characteristics:

• a resistivity between 70 and 85 pQ.cm,

• a PTE thermoelectric power with a value less than 2 pV/°C, preferably less than 1 pV/°C, more preferably still less than 0.5 pV/°C, and

• a temperature coefficient of the TCR resistance, between 20 and 50°C, between -50 and +50 ppm/°C, preferably between -40 and +40 ppm/°C, and more preferably still between -20 and +20 ppm/°C.

[0042] The invention also relates to a precision resistor comprising, on the one hand, a core obtained from a resistive alloy in accordance with the invention, and, on the other hand, copper connectors located on either side of said core and assembled, by welding, to the latter.

[0043] The invention also relates to a first embodiment of a method for manufacturing a strip of precision resistive alloy based on copper in accordance with the invention and described above, said method comprising at least the following steps, taken in order:

[0044] - Melting of the constituent elements of said alloy and continuous casting so as to obtain an ingot with a thickness or diameter of between 100 and 250 mm;

[0045] - Homogenization heat treatment operation at a temperature between 600 and 800°C for 2 to 5 h;

[0046] - From a homogenized ingot, obtaining a strip with a thickness of less than 20 mm, by dynamic hot recrystallization, comprising rolling, extrusion and forging, at a temperature between 700 and 850°C, with a section reduction ratio greater than 50%;

[0047] - Obtaining a strip with a thickness of less than 10 mm by static recrystallization after cold work hardening with a section reduction ratio of between 65 and 85%, at a temperature of between 550°C and 700°C, for a duration of between 1 and 3 hours.

[0048] In a second embodiment of the method of the invention, which is just as advantageous, it comprises at least the following steps, taken in order: [0049] - Melting of the constituent elements of said alloy and continuous casting so as to obtain a strip with a thickness of less than 20 mm;

[0050] - Homogenization heat treatment operation at a temperature between 600 and 800°C for 2 to 5 h;

[0051] - From a homogenized strip with a thickness of less than 20 mm, obtaining a strip with a thickness of less than 10 mm by static recrystallization after cold work hardening with a section reduction ratio of between 65 and 85%, at a temperature of between 550°C and 700°C, for a period of between 1 and 3 hours.

[0052] Other aims and advantages of the present invention will appear during the description which follows relating to embodiments which are given only as indicative and non-limiting examples.

[0053] Understanding of this description will be facilitated by referring to the single attached figure described below:

[0054] [Fig.1] shows curves of variation of the resistance relative to the resistance at 20°C as a function of the temperature for two alloys of the invention having the following composition:

- CuMn21 Ni6Sn1 ( — ■ — ■ — ) with 21.0% Mn, 6.0% Ni and 1.0% Sn, the remainder being copper and unavoidable impurities;

- CuMn21 Ni6SnO.5 ( — ) with 21.0% Mn, 6.0% Ni and 0.5% Sn, the remainder being copper and unavoidable impurities;

And three comparative alloys whose composition does not fall within the definition of the invention:

- CuMn23Ni3 ( - ) with 23.0% Mn and 3.0% Ni, the remainder being copper and unavoidable impurities;

- CuMnl 2Ni5Sn3 ( — ■ ■ — ■ ■ — ) with 12.0% Mn; 5.0% N, and 3.0% Sn, the remainder being copper and unavoidable impurities

- CuMn20Ni5Si ( - ) with 20.0% Mn, 5.0% Ni and Si, the remainder being copper and unavoidable impurities. [0055] The present invention relates to a copper (Cu)-based alloy for the manufacture of standard resistors or precision resistors, the latter having applications in particular in measuring devices such as shunts and strain gauges, said shunts being able to be found in the control system of accumulator batteries.

[0056] In such systems, temperature has a major effect on the charging capacity of the batteries, or even on their destruction.

[0057] Therefore for such applications it is essential to provide alloys, for the manufacture of precision resistors, having stable electrical properties in the temperature ranges to which such components are likely to be subjected.

[0058] Thus, the inventors have developed a precision resistive alloy, the majority element of which is Cu, and having the following composition, this being optimal for use in the manufacture of precision resistors and obtaining the desired thermoelectric properties:

[0059] - A proportion of manganese (Mn) between 20.0 and 23.0%,

[0060] - A proportion of nickel (Ni) between 4.5 and 8.0%,

[0061] - A proportion of tin (Sn) between 0.2 and 2.0%,

[0062] The remainder being copper and unavoidable impurities in a maximum proportion, for the latter, of 0.8%, preferably in a maximum proportion of 0.4%.

[0063] And in which alloy the ratio (in % by mass) between the proportion of Mn and Ni is between 3.0 and 5.0.

[0064] Such an alloy composition makes it possible to manufacture precision resistors having exceptional properties, in terms of both resistivity, but also TCR and PTE, and, moreover, to maintain stability of these properties in the temperature ranges to which said resistors are subjected, in use.

[0065] Thus, such an alloy composition makes it possible to manufacture electronic components having a resistivity considered to be particularly high, for such an alloy family, between 70.0 and 85.0 pQ.cm. [0066] Such resistivity values have not, until now, been achieved by alloys having a CuMnNi base and produced in the context of conventional melting processes, but only in the context of vacuum melting processes.

[0067] However, in the field of application of precision resistors, obtaining high resistivity is not sufficient.

[0068] Also, by means of the present alloy composition of the invention, the inventors have succeeded in achieving, also, optimal values in terms of temperature coefficient TCR and thermoelectric power PTE.

[0069] More specifically, the Mn/Ni ratio, between the proportions of manganese and nickel in the alloy, must be between 3 and 5, making it possible to ensure an optimal PTE and, preferably, less than 1 pV/°C.

[0070] As a reminder, the PTE reflects the appearance of a difference in electrical potential under the effect of a thermal gradient applied to the junctions of pairs of materials.

[0071] Thus, by means of the Mn/Ni ratio specific to the precision resistive alloy of the invention, a low electrical potential difference is maintained between the core of a precision resistor, obtained from said alloy, and the copper connectors assembled to said core by welding.

[0072] The proportion of tin in the resistive alloy of the invention, between 0.2 and 2.0%, makes it possible to ensure obtaining a temperature coefficient TCR of the resistance between -50 and +50 ppm/°C, in a temperature range between 20 and 50°C.

[0073] In other words, the alloy of the invention makes it possible to ensure stability of the temperature resistance, in the range of temperatures of use of a precision resistor obtained using said alloy.

[0074] Most preferably, the proportion of Sn in the alloy of the invention is between 0.6 and 1.6% by mass, which further allows adjustment of the TCR and maintenance thereof in a range between -40 and +40 ppm/°C.

[0075] More preferably still, it has been established that a proportion of tin between 0.2 and 1.0% makes it possible to obtain a particularly optimal TCR between -20 and +20 ppm/°C. [0076] The graph in Figure 1 allows us to compare two alloys in accordance with the invention, noted:

- CuMn21 Ni6Sn1 (curve — ■ — ■ — ) and comprising 21.0% Mn, 6.0% Ni and 1.0% Sn, the remainder being copper and unavoidable impurities, and

- CuMn21 Ni6SnO.5 (solid curve — ) with 21.0% Mn, 6.0% Ni and 0.5% Sn, the remainder being copper and unavoidable impurities, with three alloys of different composition: CuMn23Ni3 ( - ),

CuMn12Ni5Sn3 ( — - - ) and CuMn20Ni5Si ( - ).

[0077] This figure shows the resistance variation curves of these alloys, relative to the resistance at 20 °C as a function of temperature. From these curves, the TCR can be deduced by mathematical modeling.

[0078] It can thus be deduced from the results illustrated on these curves that the alloys of the invention each allow the obtaining of a TCR which is particularly stable and close to 0, in particular over a temperature range between 20 and 50°C.

[0079] According to an optional characteristic of the composition of the precision resistive alloy of the invention, the composition thereof also comprises, in addition to Cu, Mn, Ni and Sn, a proportion of silicon (Si) of between 0.02 and 0.15% by mass.

[0080] In this case, when the composition of the alloy of the invention incorporates a proportion of Si, it is imperative to respect the following relationship, considering the mass percentage of Sn and that of Si:

[0081] The sum of the mass percentages (Sn + 4*Si) must be less than 2.0% and, more preferably still, this sum (Sn + 4*Si) is less than 1.6%.

[0082] The introduction of Si, carried out most preferably during the process for producing the precision resistive alloy of the invention, at the end of the melting of the various constituent elements of said alloy, allows, on the one hand, a reduction in the formation of Mn oxide and, on the other hand, to reduce the oxidation of Mn during the casting step and to limit the formation of porosities which could have a harmful effect on the thermoelectric properties of the resistor. [0083] Furthermore, Si acts on the resistivity, just like Mn. Thus, the introduction of Si into the alloy of the invention makes it possible to further substantially improve the resistivity values obtained.

[0084] However, the combined effect of the Sn and Si elements on the TCR should be taken into account, which is maintained between -20 and +20 ppm/°C while respecting the above-mentioned relationship (Sn + 4*Si) < 2.0%, preferably < 1.6%.

[0085] Furthermore, the proportion of Si within the precision resistive alloy of the invention must be less than 0.15% so as to avoid embrittlement thereof during a hot transformation step implemented during the process for producing a strip, described below, from said alloy.

[0086] Indeed, the present invention also relates to a method for manufacturing a strip of precision resistive alloy based on copper as described above, consisting of the elements Mn, Ni, Sn, possibly Si, in the proportions and respecting the Mn/Ni ratio mentioned, and possibly the Si+Sn criterion introduced where appropriate, the remainder of the alloy being Cu as well as the inevitable impurities.

[0087] In a first embodiment of the method of the invention, it comprises at least the following steps, taken in order:

[0088] - Melting of the constituent elements of said alloy and semi-continuous casting so as to obtain an ingot with a thickness or diameter of between 100 and 250 mm;

[0089] - Carrying out a homogenization heat treatment operation at a temperature advantageously between 600 and 800°C, for a duration preferably between 2 and 5 hours;

[0090] - From an ingot homogenized following the previous step, obtaining a strip with a thickness of less than 20 mm, by dynamic hot recrystallization, comprising at least rolling or extrusion or forging, at a temperature advantageously between 700 and 850°C, with a section reduction ratio greater than 50%;

[0091] - Obtaining a strip with a thickness of less than 10 mm by static recrystallization after cold work hardening, with a section reduction ratio of between 65 and 85%, at a temperature advantageously of between 550°C and 700°C, for a duration of preferably between 1 and 3 hours. [0092] According to a second embodiment of the method of the invention, the latter comprises, at least, the following steps, taken in order:

[0093] - Melting of the constituent elements of said alloy and continuous casting so as to obtain a strip with a thickness of less than 20 mm;

[0094] - Carrying out a homogenization heat treatment operation at a temperature advantageously between 600 and 800°C for a duration of between 2 and 5 hours;

[0095] - From a strip with a thickness of less than 20 mm and homogenized, obtaining a strip with a thickness of less than 10 mm by static recrystallization after cold work hardening with a section reduction ratio of between 65 and 85%, at a temperature preferably of between 550°C and 700°C, for a duration advantageously of between 1 and 3 h.

[0096] Due to the specific composition of the precision resistive alloy of the invention, the method of the invention, advantageously, does not require carrying out the melting and casting in a vacuum enclosure.

[0097] In other words, in the process of the invention, conventional melting and casting are carried out, not under vacuum.

[0098] Furthermore, the implementation of this method makes it possible to reduce the heterogeneities of microstructures to allow transformations, and to ensure the homogeneity and constancy of the electrical properties of the final product obtained.

[0099] It should also be noted that a homogenization temperature of the alloy, before transformation, not exceeding 800°C, allows the CuMnSn phases rich in Sn (more than 20% Sn) to be dissolved and thus avoid their fusion, which would be likely to cause decohesion and damage during transformation.

[0100] Most preferably, when the starting alloy incorporates a proportion of Si of between 0.02% and 0.15%, respecting the criterion Sn+0.4*Si<2.0%, preferably <1.6%, the Si is introduced at the end of fusion, after introduction and fusion of the other constituent elements of the alloy, Cu, Mn, Ni and Sn.

Claims

Claims [Claim 1] (A precision resistive alloy based on copper (Cu) for the manufacture of a precision resistor, said alloy being characterized in that it consists of, in % by mass: - manganese (Mn) in a proportion of between 20.0 and 23.0%, - nickel (Ni) in a proportion of between 4.5 and 8.0%, - tin (Sn) in a proportion of between 0.2 and 2.0%, - Possibly silicon (Si) in a proportion of between 0.02 and 0.15%, then respecting Sn+4*Si<2.0%, - The remainder being copper and unavoidable impurities, - And in which alloy the ratio (in % by mass) between the proportion of Mn and Ni is between 3.0 and 5.0. [Claim 2] Precision resistive copper-based alloy according to claim 1 characterized in that the proportion of Sn is between 0.6 and 1.6%. [Claim 3] A precision copper-based resistive alloy according to claim 1 or claim 2 characterized in that the proportion of Mn is between 20.0 and 22.0%. [Claim 4] Precision resistive copper-based alloy according to any one of claims 1 to 3, characterized in that the proportion of Ni is between 5.0 and 6.5%. [Claim 5] Precision copper-based resistive alloy according to any one of claims 1 to 4, characterized in that it has a resistivity of between 70 and 85 pQ.cm, a thermoelectric power PTE with a value of less than 2 pV/°C, preferably less than 1 pV/°C, preferably less than 0.5 pV/°C, and a temperature coefficient of resistance TCR, between 20 and 50 °C, of between -50 and +50 ppm/°C, preferably of between -40 and +40 ppm/°C, preferably of between -20 and +20 ppm/°C. [Claim 6] A method of manufacturing a copper-based precision resistive alloy strip according to any one of claims 1 to 5, said alloy consisting of, in mass %, between 20.0 and 23.0% of Mn, between 4.5 and 8.0% of Ni, between 0.2 and 2.0% of Sn, optionally between 0.02 and 0.15% of Si, then respecting Sn+4*Si<2.0%, the remainder being copper and unavoidable impurities, and in which alloy the ratio between the proportion of Mn and Ni is between 3.0 and 5.0, said method being characterized in that it comprises, at least, the following steps, taken in order: - Melting of the constituent elements of said alloy and semi-continuous casting so as to obtain an ingot with a thickness or diameter of between 100 and 250 mm; - Homogenization heat treatment operation at a temperature between 600 and 800°C for 2 to 5 hours; - From a homogenized ingot, obtaining a strip with a thickness of less than 20 mm, by dynamic hot recrystallization, including rolling, extrusion and forging, at a temperature between 700 and 850 °C, with a section reduction ratio greater than 50% - Obtaining a strip with a thickness of less than 10 mm by static recrystallization after cold work hardening with a section reduction ratio of between 65 and 85%, at a temperature of between 550°C and 700°C, for a duration of between 1 and 3 hours. [Claim 7] A method of manufacturing a copper-based precision resistive alloy strip according to any one of claims 1 to 5, said alloy consisting of, in mass %, between 20.0 and 23.0% of Mn, between 4.5 and 8.0% of Ni, between 0.2 and 2.0% of Sn, optionally between 0.02 and 0.15% of Si, then respecting Sn+4*Si<2.0%, the remainder being copper and unavoidable impurities, and in which alloy the ratio between the proportion of Mn and Ni is between 3.0 and 5.0, said method being characterized in that it comprises: - Fusion of the constituent elements of said alloy and continuous casting so as to obtain a strip with a thickness of less than 20 mm; - Homogenization heat treatment operation at a temperature between 600 and 800°C for 2 to 5 hours; - From a homogenized strip with a thickness of less than 20 mm, obtaining a strip with a thickness of less than 10 mm by static recrystallization after cold work hardening with a section reduction ratio of between 65 and 85%, at a temperature of between 550 °C and 700 °C, for a duration of between 1 and 3 h. ]