Precision resistance alloy based on copper, manganese, nickel and tin

Abstract

The invention discloses a precise resistance alloy based on copper, manganese, nickel and tin. A copper (Cu)-based precision resistance alloy for manufacturing precision resistors, characterized in that it consists, in mass%, of:-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%,-optionally silicon (Si) in a proportion of between 0.02% and 0.15%, with Sn + 4 * Silt; the balance is copper and unavoidable impurities, and the ratio (in mass%) of Mn and Ni in the copper-based precision resistance alloy is between 3.0 and 5.0. The alloy of the invention can be used in particular for the manufacture of precision resistors for applications in battery management systems, shunts or strain gauges.

Description

[0001] Implementation

[0002] This invention relates to the field of copper-based resistance alloys, and more specifically, resistance alloys whose main components are copper and manganese, and which also include nickel, tin, and optionally silicon.

[0003] The electrical properties of copper and manganese alloys are well known, and more specifically, they relate to their resistivity.

[0004] In so-called "precision" resistance alloys, the essential characteristics beyond resistance are the temperature coefficient of resistance (TCR) and the thermoelectric potential (TEP).

[0005] More precisely, this invention relates to an alloy that exhibits optimal stability of its resistivity, a very low temperature coefficient, and a very small thermoelectric potential after prolonged exposure to temperature (hundreds of hours) of use, and will be used in precision resistors for measuring current or in standard resistors.

[0006] Therefore, this alloy will be used specifically in the manufacture of precision resistors, such as shunts (or current dividers), which are particularly important in battery management systems (BMS), where temperature has a significant impact on the battery's charging capacity, or may even destroy it.

[0007] This alloy can also be used to manufacture chip-based precision resistors (or SMD - surface mount resistors and chip resistors), such as metal foil resistors or current sensing resistors.

[0008] Finally, this alloy will also be used in the manufacture of strain gauges that require high precision and temperature stability.

[0009] The shunt consists specifically of a core made of a resistance alloy and two copper connectors, which are assembled to the core by soldering. The potential difference between the material of the core and the copper connectors affects the TEP, and this potential difference must be as low as possible.

[0010] In other words, thermoelectric potential reflects the potential difference that appears between a pair of materials under the influence of a temperature gradient.

[0011] In the target application, namely in precision resistors, the goal is to seek the lowest possible TEP to avoid the presence of parasitic currents, which are detrimental to certain applications with parallel high resistivity values.

[0012] In contrast to conductivity, resistivity, expressed as ρ, defines a material’s ability to block charge from passing through and thus block current from passing through.

[0013] Copper has a very low resistivity ρ (1.724 μΩ·cm in the annealed state), which makes it an excellent conductor. In fact, the conductivity of copper is defined as equal to 100% IACS (International Standard for Annealed Copper).

[0014] Finally, the temperature coefficient TC represents the change in physical properties as a function of temperature, such as the thermal conductivity of a material, the mechanical strength of a conductor, or its electrical resistance.

[0015] In the application of this invention, the physical quantity of interest is the temperature coefficient of resistance (TCR); therefore, this property will be measured and the lowest possible value will be sought.

[0016] In copper alloys, manganese can be added to increase the resistivity and thermoelectric potential of the alloy while reducing the temperature coefficient.

[0017] Adding nickel to the aforementioned alloy increases resistivity, though less so than manganese, and also reduces thermoelectric potential.

[0018] Depending on the combination of components and temperature range, TCR can be negative, positive, or zero.

[0019] Tin and silicon can also be added, with the ratio of tin to silicon ranging from 3% by mass to 1% by mass, to adjust the temperature coefficient of resistance, thermoelectric potential, and improve the temperature stability of resistivity.

[0020] Therefore, in particular, U.S. Patent Application Publication No. US2020 / 224293 is known to be a resistive element made of an alloy comprising copper, manganese in proportions between 23% and 28%, nickel in proportions between 9% and 13%, and tin in proportions up to 1%.

[0021] Silicon may also be added, up to a maximum of 1%.

[0022] This yields an alloy that makes it possible for the final product to have an interesting resistivity of approximately 90 μΩ·cm.

[0023] However, precision resistance alloys containing a high proportion of manganese have disadvantages.

[0024] Specifically, the production of such alloys requires vacuum melting or a controlled atmosphere of elements to avoid the formation of oxides such as MnO, which could alter the alloy's properties. In addition to melting, transferring the molten alloy to an ingot mold often requires the use of techniques that prevent air from passing through (source processes).

[0025] However, precision resistance alloys containing a high proportion of manganese have disadvantages.

[0026] Specifically, the production of such alloys requires vacuum melting or a controlled atmosphere of elements to avoid the formation of oxides such as MnO, which could alter the alloy's properties. In addition to melting, transferring the molten alloy to an ingot mold often requires the use of techniques that prevent air from passing through (source processes).

[0027] However, the melting and vacuum casting steps require the use of specific equipment (vacuum chamber, atmospheric control), which is particularly expensive.

[0028] Furthermore, the stability of the temperature coefficient (TCR) and thermoelectric potential (TEP) still needs to be improved in order to provide an alloy with the optimal composition for manufacturing precision resistors.

[0029] Other alloy systems known in the prior art, particularly those containing between 6% and 10% manganese and between 3% and 9% aluminum, are used in resistor manufacturing applications.

[0030] In other words, the resistivity values ​​obtained for this type of alloy are relatively low, typically between 25 μΩ·cm and 55 μΩ·cm, which is not very interesting for the target application.

[0031] The same applies to CuMnSn alloys, which contain between 5% and 12% manganese and 1% to 7% tin, and whose resistivity is concentrated around 30 μΩ·cm.

[0032] The present invention aims to provide a copper-based alloy, the composition of which is further composed of at least manganese, nickel and tin, for use in the production of precision resistors having a high resistivity of at least 70 μΩ·cm, low TEP and optimal TCR in a temperature range of 20°C to 50°C, while also having a resistivity that remains stable over time.

[0033] Therefore, the present invention relates to a copper (Cu)-based precision resistance alloy for manufacturing precision resistors, characterized in that the alloy comprises, by weight percent, the following:

[0034] - Manganese (Mn) in proportions between 20.0% and 23.0%,

[0035] - Nickel (Ni) in proportions between 4.5% and 8.0%,

[0036] - Tin (Sn) in proportions between 0.2% and 2.0%,

[0037] - Optionally, the proportion of silicon (Si) is between 0.02% and 0.15%, where Sn+4*Si < 2.0%.

[0038] The remainder consists of copper and unavoidable impurities.

[0039] Furthermore, the ratio (in mass%) between Mn and Ni in the precision resistance alloy is between 3.0 and 5.0.

[0040] Specific embodiments of the precision resistance alloy according to the present invention:

[0041] - The Sn content in the alloy is between 0.6 wt% and 1.6 wt%;

[0042] - The proportion of Mn in the alloy is between 20.0% and 22.0% by weight;

[0043] - The proportion of Ni in the alloy is between 5.0% and 6.5% by weight;

[0044] -This alloy has the following properties:

[0045] ● Resistivity is between 70 μΩ·cm and 85 μΩ·cm

[0046] ● The thermoelectric potential (TEP) is less than 2 μV / ℃, preferably less than 1 μV / ℃, more preferably less than 0.5 μV / ℃, and

[0047] ● The temperature coefficient of resistance (TCR) is between 20°C and 50°C, between -50 ppm / °C and +50 ppm / °C, preferably between -40 ppm / °C and +40 ppm / °C, and even more preferably between -20 ppm / °C and +20 ppm / °C.

[0048] The present invention also relates to a precision resistor, which on one hand comprises a core obtained from the resistive alloy of the present invention, and on the other hand comprises a copper connector located on either side of the core and assembled thereon by welding.

[0049] The present invention also relates to a first embodiment of a method for manufacturing a strip of copper-based resistance alloy according to the present invention and described above, the method comprising at least the following steps performed in sequence:

[0050] - Melt the constituent elements of the alloy and continuously cast to obtain an ingot with a thickness or diameter between 100 mm and 250 mm;

[0051] - Homogenization heat treatment operation at a temperature between 600℃ and 800℃ for 2 to 5 hours;

[0052] - Obtain strips with a thickness of less than 20 mm from homogenized ingots through dynamic thermal recrystallization, wherein the dynamic thermal recrystallization includes rolling, extrusion and forging at a cross-sectional reduction rate of more than 50% at a temperature between 700°C and 850°C.

[0053] - Through static recrystallization after cold hardening, at a reduction rate between 65% and 85%, at a temperature between 550°C and 700°C, for a duration between 1 hour and 3 hours, a strip with a thickness of less than 10 mm is obtained.

[0054] In a second embodiment of the method of the present invention, and advantageously, it includes at least the following steps taken in sequence:

[0055] - Melt the constituent elements of the alloy and continuously cast to obtain strip with a thickness of less than 20 mm;

[0056] - Homogenization heat treatment operation at a temperature between 600℃ and 800℃ for 2 to 5 hours;

[0057] -From homogenized strip with a thickness of less than 20 mm, through static recrystallization after cold curing, at a reduction rate between 65% and 85%, at a temperature between 550°C and 700°C for a duration between 1 h and 3 h, a strip with a thickness of less than 10 mm is obtained.

[0058] Further objects and advantages of the present invention will become apparent from the following description of embodiments, which are provided as indicative and non-limiting examples only.

[0059] Referring to the accompanying drawings will help in understanding this specification, wherein:

[0060] [ Figure 1 The following curves show the change in resistance relative to resistance at 20°C as a function of temperature for two alloys of the present invention having the following compositions:

[0061] -CuMn21Ni6Sn1(―·―·―), containing 21.0% Mn, 6.0% Ni and 1.0% Sn, with the remainder being copper and unavoidable impurities;

[0062] -CuMn21Ni6Sn0.5(―) contains 21.0% Mn, 6.0% Ni and 0.5% Sn, with the remainder being copper and unavoidable impurities;

[0063] And three comparative alloys whose compositions do not fall within the definition of this invention:

[0064] -CuMn23Ni3(―――), containing 23.0% Mn and 3.0% Ni, with the remainder being copper and unavoidable impurities;

[0065] -CuMn12Ni5Sn3(―··―··―), containing 12.0% Mn, 5.0% Ni and 3.0% Sn, with the remainder being copper and unavoidable impurities.

[0066] -CuMn20Ni5Si(-------) has 20.0% Mn, 5.0% Ni and Si, with the remainder being copper and unavoidable impurities.

[0067] This invention relates to a copper (Cu) based alloy for manufacturing standard or precision resistors, particularly for use in measuring devices such as shunts and strain gauges, which may be present in battery management systems.

[0068] In such systems, temperature has a major impact on the battery's charging capacity, or can even cause its destruction.

[0069] Therefore, for such applications, it is important to propose alloys for manufacturing precision resistors that have stable electrical properties over the temperature range that these components may be subjected to.

[0070] Therefore, the inventors have developed a precision resistance alloy whose main element is Cu and has the following composition, which is optimal for use in the manufacture of precision resistors and for obtaining the desired thermoelectric properties:

[0071] - The proportion of manganese (Mn) between 20.0% and 23.0%,

[0072] - Nickel (Ni) content between 4.5% and 8.0%,

[0073] - A tin (Sn) ratio between 0.2% and 2.0%,

[0074] The remainder consists of copper and unavoidable impurities, the latter being no more than 0.8%, preferably no more than 0.4%.

[0075] Furthermore, the ratio (in mass%) between Mn and Ni in this precision resistance alloy is between 3.0 and 5.0.

[0076] Such an alloy composition makes it possible to manufacture precision resistors with excellent resistivity, TCR and TEP, and furthermore, to maintain the stability of these properties over the temperature range that the resistor is subjected to during use.

[0077] Therefore, this alloy composition can be used to manufacture electronic components with particularly high resistivity, ranging from 70.0 μΩ·cm to 85.0 μΩ·cm for this alloy series.

[0078] To date, no CuMnNi-based alloy has achieved such a resistivity value. These alloys were all developed using traditional melting methods, and such a resistivity value can only be achieved during vacuum melting.

[0079] In other words, high resistivity is not sufficient in the application of precision resistors.

[0080] Furthermore, through the alloy composition of this invention, the inventors have also achieved optimal values ​​for the temperature coefficient (TCR) and the thermoelectric potential (TEP).

[0081] More specifically, the Mn / Ni ratio, the ratio of manganese to nickel in the alloy, must be between 3 and 5 to ensure optimal TEP and a better coefficient of less than 1 μV / ℃.

[0082] It should be noted that TEP reflects the potential difference that appears at the interface between a pair of materials under the action of a thermal gradient.

[0083] Therefore, through the specific Mn / Ni ratio of the precision resistor alloy of the present invention, a low potential difference is maintained between the core of the precision resistor obtained from the alloy and the copper connector assembled to the core by welding.

[0084] The proportion of tin in the resistance alloy of the present invention is between 0.2% and 2.0%, which ensures that the temperature coefficient of resistance (TCR) is between -50 ppm / ℃ and +50 ppm / ℃ in a temperature range between 20℃ and 50℃.

[0085] In other words, the alloy of the present invention maintains the temperature stability of the resistor within the temperature range of the precision resistor obtained through the alloy.

[0086] Preferably, the Sn content in the alloy of the present invention is between 0.6% and 1.6%, which also allows the TCR to be set and maintained in the range between -40ppm / ℃ and 40ppm / ℃.

[0087] Even better, it is still possible to establish a tin ratio between 0.2% and 1.0% to make it possible to obtain a particularly optimal TCR between -20ppm / ℃ and 20ppm / ℃.

[0088] Figure 1 The accompanying drawings allow for a comparison of the two alloys according to the invention, represented by the following formula:

[0089] -CuMn21Ni6Sn1 (curve —) and contains 21.0% Mn, 6.0% Ni and 1.0% Sn, the remainder being copper and unavoidable impurities; and

[0090] -CuMn21Ni6Sn0.5 (solid curve—), containing 21.0% Mn, 6.0% Ni and 0.5% Sn, with the remainder being copper and unavoidable impurities.

[0091] Three alloys with different compositions were used: CuMn23Ni3 (―――), CuMn12Ni5Sn3 (―··―··―), and CuMn20Ni5Si (-------).

[0092] The figure shows the resistance of these alloys as a function of temperature at 20°C. Based on these curves, the resistance coefficient (TCR) can be derived through mathematical modeling.

[0093] Therefore, it can be inferred from the results shown on these curves that the alloys of the present invention each make it possible to obtain a particularly stable TCR close to 0, especially in the temperature range between 20°C and 50°C.

[0094] The optional feature of the composition of the precision resistance alloy according to the present invention, in addition to Cu, Mn, Ni and Sn, also includes a silicon (Si) proportion between 0.02% by mass and 0.15% by mass.

[0095] In this case, when the alloy of the present invention contains a certain proportion of Si, considering the mass percentage of Sn and the mass percentage of Si, the following relationship must be followed:

[0096] The total mass percentage (Sn+4*Si) must be less than 2.0%, and more preferably less than 1.6%.

[0097] At the end of melting the various constituent elements of the alloy, the introduction of Si, preferably carried out during the preparation method of the resistance alloy of the present invention, can reduce the formation of Mn oxide on the one hand, reduce the oxidation of Mn during the casting step on the other hand, and limit the formation of pores that may have an adverse effect on the thermoelectric performance of the resistor.

[0098] Furthermore, Si affects resistivity, just like Mn. Therefore, introducing Si into the alloy of the present invention allows for further improvement of the obtained resistivity value.

[0099] However, considering that the combined effect of elements Sn and Si on TCR is appropriate, it is maintained between -20ppm / ℃ and +20ppm / ℃, while conforming to the above relationship (Sn+4*Si)<2.0%, preferably <1.6%.

[0100] Furthermore, the proportion of Si in the resistance alloy of the present invention must be less than 0.15% to avoid weakening the alloy during the thermal transformation step in the method of manufacturing strip from the alloy.

[0101] In fact, the present invention also relates to a method for manufacturing the copper-based precision resistance alloy strip as described above, the copper-based precision resistance alloy being composed of elements Mn, Ni, Sn, and optionally Si in a certain proportion and conforming to the Mn / Ni ratio, and optionally, introducing standard Si+Sn, the remainder of the alloy being Cu and unavoidable impurities where applicable.

[0102] In a first embodiment of the method of the present invention, the latter includes at least the following steps taken in sequence:

[0103] - Melt the constituent elements of the alloy and semi-continuously cast to obtain an ingot with a thickness or diameter between 100 mm and 250 mm;

[0104] - The homogenization heat treatment operation is carried out at a temperature between 600°C and 800°C, preferably for a time between 2 hours and 5 hours.

[0105] - From the ingot homogenized according to the aforementioned steps, a strip with a thickness of less than 20 mm is obtained through dynamic thermal recrystallization, wherein the dynamic thermal recrystallization includes at least rolling, extrusion or forging, at an advantageous temperature of 700°C to 850°C, with a cross-sectional reduction rate of more than 50%.

[0106] - Through static recrystallization after cold hardening, at a reduction rate between 65% and 85%, at a temperature between 550°C and 700°C, and for a duration preferably between 1 hour and 3 hours, strips with a thickness of less than 10 mm are obtained.

[0107] In a second embodiment of the method of the present invention, the method includes at least the following steps taken in sequence:

[0108] - Melt the constituent elements of the alloy and continuously cast to obtain strip with a thickness of less than 20 mm;

[0109] - The homogenization heat treatment operation is carried out at a temperature between 600°C and 800°C, preferably for a time between 2 hours and 5 hours.

[0110] -From a homogenized strip with a thickness of less than 20 mm, through static recrystallization after cold curing, a strip with a thickness of less than 10 mm is obtained at a reduction rate of 65% to 85%, preferably at a temperature between 550°C and 700°C, for a duration advantageously between 1 h and 3 h.

[0111] Due to the specific composition of the precision resistance alloy of the present invention, the method of the present invention advantageously eliminates the need for melting and casting in a vacuum chamber.

[0112] In other words, the conventional melting and casting are not performed under vacuum in the method of this invention.

[0113] Furthermore, the implementation of this method allows for the reduction of inhomogeneities in the microstructure to permit transformation, and ensures the uniformity and consistency of the electrical properties of the final product.

[0114] It should also be noted that, prior to the transformation, a homogenization temperature of no more than 800°C for the alloy allows for the dissolution of the Sn-rich CuMnSn phase (more than 20% Sn), thus preventing their melting, which could lead to stripping and damage during the transformation.

[0115] Ideally, when the proportion of Si in the initial alloy is between 0.02% and 0.15%, and simultaneously meets the criteria of Sn + 0.4 * Si < 2.0%, preferably < 1.6%, Si is added at the end of the melting process, that is, after the other constituent elements Cu, Mn, Ni and Sn of the alloy are introduced and melted.

Claims

1. A copper (Cu)-based precision resistance alloy for manufacturing precision resistors, characterized in that, The alloy, by mass percent, consists of the following: - Manganese (Mn) in proportions between 20.0% and 23.0%, - Nickel (Ni) in proportions between 4.5% and 8.0%, - Tin (Sn) in proportions between 0.2% and 2.0%, - Optionally, the proportion of silicon (Si) is between 0.02% and 0.15%, where Sn+4*Si < 2.0%. - The remainder consists of copper and unavoidable impurities. - Furthermore, the ratio (in mass%) between Mn and Ni in this copper-based precision resistance alloy is between 3.0 and 5.

0.

2. The copper-based precision resistance alloy as claimed in claim 1, wherein, The proportion of Sn is between 0.6% and 1.6%.

3. The copper-based precision resistance alloy as claimed in claim 1 or claim 2, wherein, The proportion of Mn is between 20.0% and 22.0%.

4. The copper-based precision resistance alloy according to any one of claims 1 to 3, wherein, The proportion of Ni is between 5.0% and 6.5%.

5. The copper-based precision resistance alloy according to any one of claims 1 to 4, wherein, The resistivity of this copper-based precision resistance alloy is between 70 μΩ·cm and 85 μΩ·cm, the thermoelectric power (TEP) value is less than 2 μV / ℃, preferably less than 1 μV / ℃, more preferably less than 0.5 μV / ℃, and the temperature coefficient of resistance (TCR) is between 20℃ and 50℃, between -50ppm / ℃ and +50ppm / ℃, preferably between -40ppm / ℃ and +40ppm / ℃, and more preferably between -20ppm / ℃ and +20ppm / ℃.

6. A method for manufacturing a strip of a copper-based resistance alloy as claimed in any one of claims 1 to 5, the alloy comprising, by mass percent, between 20.0% and 23.0% Mn, between 4.5% and 8.0% Ni, between 0.2% and 2.0% Sn, optionally between 0.02% and 0.15% Si, satisfying Sn+4*Si<2.0%, with the remainder being copper and unavoidable impurities, and the ratio of Mn to Ni in the copper-based resistance alloy being between 3.0 and 5.0, characterized in that the method comprises, at least sequentially, the following steps: - Melt the constituent elements of the alloy and semi-continuously cast to obtain ingots with a thickness or diameter between 100 mm and 250 mm. - Homogenization heat treatment operation at a temperature between 600℃ and 800℃ for 2 to 5 hours; - Obtain strips with a thickness of less than 20 mm from homogenized ingots by dynamic thermal recrystallization, which involves rolling, extrusion and forging at a cross-sectional reduction rate of greater than 50% at a temperature between 700°C and 850°C. - By static recrystallization after cold hardening, at a reduction rate between 65% and 85%, at a temperature between 550°C and 700°C, for a duration between 1 hour and 3 hours, a strip with a thickness of less than 10 mm is obtained.

7. A method for manufacturing a strip of a copper-based resistance alloy as claimed in any one of claims 1 to 5, the alloy comprising, by mass percent, between 20.0% and 23.0% Mn, between 4.5% and 8.0% Ni, between 0.2% and 2.0% Sn, optionally between 0.02% and 0.15% Si, conforming to Sn + 4*Si < 2.0%, the remainder being copper and unavoidable impurities, wherein the ratio of Mn to Ni in the copper-based resistance alloy is between 3.0 and 5.0, the method characterized in that it comprises: - Melt the constituent elements of the alloy and continuously cast to obtain strips with a thickness of less than 20 mm; - Homogenization heat treatment operation at a temperature between 600℃ and 800℃ for 2 to 5 hours; -From homogenized strip with a thickness of less than 20 mm, through static recrystallization after cold hardening, at a reduction rate between 65% and 85%, at a temperature between 550°C and 700°C for a duration between 1 h and 3 h, strip with a thickness of less than 10 mm is obtained.

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