Copper, manganese, nickel, and tin-based precision resistance alloys

Abstract

A copper (Cu)-based precision resistor alloy for the manufacture of precision resistors, wherein the alloy is in mass %: Manganese (Mn) in a proportion between -20.0% and 23.0% Nickel (Ni) in a proportion between -4.5% and 8.0% -Tin (Sn) in a percentage between -0.2% and 2.0% - Characterized by being selectively composed of silicon (Si) in proportions between 0.02% and 0.15%, provided that Sn+4*Si<2.0%, The remainder consists of copper and unavoidable impurities. In alloys, the ratio (in mass percent) of Mn to Ni is between 3.0 and 5.0. The alloy of the present invention can be particularly used in the manufacture of precision resistors for applications in battery management systems, shunts, or strain gauges.

Description

Technical Field

[0001] The present invention relates to copper-based resistance alloys, particularly to the field of resistance alloys whose main components are copper and manganese and which also contain nickel, tin, and optionally silicon.

Background Art

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

[0003] In so-called "precision" resistance alloys, the essential characteristics beyond resistance are the temperature coefficient of resistance (TCR) and the thermoelectric power (TEP).

[0004] More specifically, the present invention relates to an alloy having optimal stability of its resistivity, a very low temperature coefficient, and a very small thermoelectric power after exposure to temperature over a long period (hundreds of hours) of use, which would be used in precision resistors or standard resistors for the measurement of current.

[0005] Therefore, such an alloy will find particular use in the manufacture of precision resistors such as shunts (or microshunts) that are particularly essential in battery management systems (BMS) where temperature has a major impact on, or can even destroy, the capacity of the battery.

[0006] This alloy can also be used in the manufacture of chip-based precision resistors (or surface mount resistors (SMD) and chip resistors) such as metal foil resistors or current sensing resistors.

[0007] Finally, this alloy will also find use in the manufacture of strain gauges for measurements requiring high precision and temperature stability.

[0008] The shunt consists, in particular, of a core manufactured from a resistance alloy and two copper connectors, the connectors being assembled to the core by welding, and the potential difference between the core and the copper connector materials that affects TEP must be as low as possible.

[0009] In other words, thermoelectric power reflects the emergence of a potential difference between a pair of materials exposed to a temperature gradient.

[0010] In the target application, namely precision resistors, the lowest possible TEP (Temperature Efficiency) is required to avoid the presence of high resistance values ​​in parallel with parasitic currents that are detrimental to specific applications.

[0011] In contrast to conductivity, resistivity, denoted as ρ, defines a material's ability to block the passage of electric charge, or electric current.

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

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

[0014] In the applications of this invention, the physical quantity of interest is the temperature coefficient of resistance (TCR), and therefore it is this characteristic that is measured, and it is required to achieve the lowest possible value for it.

[0015] In alloys where copper is the main component, manganese can be added to the copper, increasing the resistivity and thermoelectric power of the alloy while simultaneously lowering the temperature coefficient.

[0016] The addition of nickel to the aforementioned alloy has the effect of increasing resistivity, but to a lesser extent than that of manganese, and on the other hand, it has the effect of lowering thermoelectric power.

[0017] TCR can be negative, positive, or zero depending on the combination of elements and temperature range.

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

[0019] Therefore, in particular, a U.S. patent application published under the number US2020 / 224293 is known, relating to a resistive element manufactured from an alloy containing copper, manganese in proportions between 23 and 28%, nickel in proportions between 9 and 13%, and tin in proportions up to 1%.

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

[0021] The alloy is thus obtained, which makes it possible to give the final product an interesting resistivity on the order of 90 μΩ.cm.

[0022] However, precision resistance alloys containing a high percentage of manganese have drawbacks.

[0023] In particular, such alloys require vacuum melting or an element-controlled atmosphere during their production to avoid the formation of MnO oxides, which can alter the alloy's properties. In addition to melting, the transfer of the liquid alloy to the ingot mold requires the frequent use of techniques (source processes) that do not allow air to pass through.

[0024] However, carrying out the melting and vacuum casting steps has the disadvantage of requiring the use of specific equipment (vacuum chamber, atmosphere control), which are particularly expensive.

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

[0026] In the prior art, other alloys are known which have a composition for use in the manufacture of resistors, in particular containing between 6 and 10% manganese and between 3 and 9% aluminium.

[0027] However, in the case of such alloys, the resulting resistivity values are relatively low and not very interesting for the intended applications, usually being between 25 μΩ.cm and 55 μΩ.cm.

[0028] The same applies to CuMnSn alloys, which have a composition containing between 5 and 12% manganese and between 1 and 7% tin, whereby the resistivity values are centred around 30 μΩ.cm. SUMMARY OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION

[0029] The present invention aims to propose a copper-based alloy having a composition further composed of at least manganese, nickel and tin, for the manufacture of precision resistors having a high resistivity of at least 70 μΩ.cm in the temperature range from 20 °C to 50 °C, both a low TEP and an optimal TCR, and on the other hand a resistivity stable over time. MEANS FOR SOLVING THE PROBLEM

[0030] To achieve this object, the present invention is a copper (Cu)-based precision resistance alloy for the manufacture of precision resistors, said alloy consisting in mass % of the following:

[0031] Manganese (Mn) is in a proportion between 20.0% and 23.0%,

[0032] Nickel (Ni) is in a proportion between 4.5% and 8.0%,

[0033] The tin (Sn) content is between 0.2% and 2.0%.

[0034] Selectively, silicon (Si) is present in a proportion between 0.02% and 0.15%, where Sn+4*Si<2.0%.

[0035] The remainder consists of copper and unavoidable impurities.

[0036] This invention relates to a copper-based precision resistance alloy characterized by a manganese-to-nickel ratio (mass%) between 3.0 and 5.0.

[0037] According to a specific embodiment of the precision resistance alloy of the present invention:

[0038] The proportion of Sn in the alloy is between 0.6% by weight and 1.6% by weight;

[0039] The proportion of Mn in the alloy is between 20.0% by weight and 22.0% by weight;

[0040] The proportion of Ni in the alloy is between 5.0% and 6.5% by weight;

[0041] The aforementioned alloy has the following characteristics: Resistivity between 70 μΩ.cm and 85 μΩ.cm Thermoelectric power TEP having a value of less than 2 μV / °C, preferably less than 1 μV / °C, and more preferably less than 0.5 μV / °C, A temperature coefficient of resistance (TCR) between 20°C and 50°C, ranging from -50 ppm / °C to +50 ppm / °C, preferably between -40 ppm / °C and +40 ppm / °C, and more preferably between -20 ppm / °C and +20 ppm / °C.

[0042] The present invention also relates to a precision resistor comprising, on the one hand, a core obtained from the resistive alloy of the present invention, and on the other hand, copper connectors located on both sides of the core and assembled thereto by welding.

[0043] The present invention is also related, in accordance with the present invention, to a first embodiment of a method for manufacturing copper-based resistance alloy strips, the method comprising at least the following steps, which are carried out in order:

[0044] - Melting the constituent elements of the alloy and continuous casting to obtain ingots having a thickness or diameter between 100 mm and 250 mm;

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

[0046] - From homogenized ingots, strips with a thickness of less than 20 mm are obtained by dynamic thermal recrystallization, including rolling, extrusion, and forging, at temperatures between 700°C and 850°C, with a cross-sectional reduction rate of more than 50%;

[0047] After low-temperature curing at a temperature between -550°C and 700°C over a period of 1 to 3 hours with a reduction rate between 65% and 85%, static recrystallization is performed to obtain strips with a thickness of less than 10 mm.

[0048] A second embodiment of the method of the present invention is equally advantageous, comprising at least the following steps performed in order:

[0049] - Continuous casting to melt the constituent elements of the alloy and obtain strips having a thickness of less than 20 mm;

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

[0051] From a homogenized strip having a thickness of less than -20 mm, a strip with a thickness of less than 10 mm is obtained by low-temperature curing at a temperature between 550°C and 700°C for a period between 1 hour and 3 hours with a reduction rate between 65% and 85%, followed by static recrystallization.

[0052] Further objectives and advantages of the present invention will become apparent through the following description relating to embodiments provided only as non-limiting examples.

[0053] Understanding this explanation will be facilitated by referring to the attached diagram: [Brief explanation of the drawing]

[0054] [Figure 1] Figure 1 shows the curve of the change in resistance as a function of temperature at 20°C for two alloys of the present invention having the following compositions: CuMn21Ni6Sn1(―·―·―), having 21.0% Mn, 6.0% Ni, and 1.0% Sn, with the remainder being copper and unavoidable impurities; and CuMn21Ni6Sn0.5(―), having 21.0% Mn, 6.0% Ni, and 0.5% Sn, with the remainder being copper and unavoidable impurities. Three comparative alloys whose compositions do not fall within the definition of the present invention: CuMn23Ni3(― ― ―), having 23.0% Mn and 3.0% Ni, with the remainder being copper and unavoidable impurities. CuMn12Ni5Sn3 (―··―··―), which has 12.0% Mn, 5.0% Ni, and 3.0% Sn, with the remainder being copper and unavoidable impurities. CuMn20Ni5Si (-------), which has 20.0% Mn, 5.0% Ni, and Si, with the remainder being copper and unavoidable impurities. [Modes for carrying out the invention]

[0055] The present invention relates to copper (Cu)-based alloys for the manufacture of standard resistors or precision resistors, the latter having applications particularly in measuring devices such as shunts and strain gauges, the shunts potentially found in battery management systems.

[0056] In such systems, temperature has a major impact on the battery's charging capacity, or can even cause its destruction.

[0057] Therefore, for such applications, it is essential to propose alloys that possess stable electrical properties over the temperature range to which these components are likely to be exposed, in order to manufacture precision resistors.

[0058] Therefore, the inventors have developed a precision resistance alloy in which the dominant element is copper and which has the following optimal composition for use in the manufacture of precision resistors to obtain desired thermoelectric properties.

[0059] The percentage of manganese (Mn) between 20.0% and 23.0%.

[0060] The percentage of nickel (Ni) between 4.5% and 8.0%

[0061] The percentage of tin (Sn) between 0.2% and 2.0%.

[0062] The remainder consists of copper and unavoidable impurities, the latter in a proportion of 0.8% or less, preferably 0.4% or less.

[0063] In that alloy, the ratio (in mass%) of Mn to Ni is between 3.0 and 5.0.

[0064] Such alloy compositions enable the manufacture of precision resistors with exceptional properties not only in terms of resistivity but also in terms of TCR and TEP, and furthermore, enable the stability of these properties over the temperature range to which the resistor is exposed during use.

[0065] Therefore, such alloy compositions make it possible to manufacture electronic components with resistivity ranging from 70.0 μΩ.cm to 85.0 μΩ.cm, which is considered particularly high within such alloy families.

[0066] Such resistivity values ​​have not been achieved to date with alloys based on CuMnNi developed within conventional fusion methods, but only in the context of vacuum fusion processes.

[0067] That being said, high resistivity is not sufficient in the field of precision resistor applications.

[0068] Furthermore, with the current alloy composition of the present invention, the inventors have also achieved optimal values ​​for the temperature coefficient TCR and thermoelectric power TEP.

[0069] More specifically, the Mn / Ni ratio between manganese and nickel in the alloy must be between 3 and 5, which preferably ensures an optimal TEP of less than 1 μV / °C.

[0070] To reiterate, TEP reflects the emergence of a potential difference under the influence of a thermal gradient applied to the junction of a pair of materials.

[0071] Therefore, a specific Mn / Ni ratio for the precision resistance alloy of the present invention maintains a low potential difference between the core of the precision resistor obtained from the alloy and the copper connector assembled to the core by welding.

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

[0073] In other words, the alloy of the present invention ensures the temperature stability of the resistance within the operating temperature range of the precision resistor obtained using the alloy.

[0074] In particular, the proportion of tin in the alloy of the present invention is between 0.6 mass% and 1.6 mass%, which also allows the TCR to be set and maintained within the range of -40 ppm / °C and +40 ppm / °C.

[0075] More preferably, the tin ratio can be set between 0.2% and 1.0%, making it possible to obtain a particularly optimal TCR between -20 ppm / °C and +20 ppm / °C.

[0076] The graph in Figure 1 shows the two alloys according to the present invention, as shown below: -Containing 21.0% Mn, 6.0% Ni, and 1.0% Sn, the remainder being copper and the unavoidable impurity CuMn21Ni6Sn1 (curve ---); It contains -21.0% Mn, 6.0% Ni, and 0.5% Sn, with the remainder being copper and the unavoidable impurity CuMn21Ni6Sn0.5 (real curve -), This allows for a comparison of three alloys with different compositions: CuMn23Ni3(― ― ―), CuMn12Ni5Sn3(―··―··―), and CuMn20Ni5Si(-------).

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

[0078] From the results shown on these curves, it can be inferred that each of the alloys of the present invention enables the acquisition of a particularly stable TCR close to 0, especially over a temperature range that includes between 20°C and 50°C.

[0079] According to the selective compositional features of the precision resistance alloy of the present invention, its composition includes not only Cu, Mn, Ni, and Sn, but also silicon (Si) in a proportion between 0.02 mass% and 0.15 mass%.

[0080] In this case, when the composition of the alloy of the present invention includes a proportion of silicon, it is essential to adhere to the following relationship, taking into account the mass percentage of tin and that of silicon:

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

[0082] The introduction of silicon is carried out with the highest priority in the method for producing the resistance alloy of the present invention, at the final stage of dissolving the various constituent elements of the alloy, thereby reducing the formation of Mn oxide on the one hand, and reducing the oxidation of Mn during the casting step on the other hand, and limiting the formation of porosity which may have a detrimental effect on the thermoelectric properties of the resistor.

[0083] Furthermore, silicon acts on resistivity just like manganese. Therefore, the introduction of silicon into the alloy of this invention allows for a further improvement in the resulting resistivity value.

[0084] However, while the aforementioned relationship (Sn+4*Si) < 2.0%, preferably < 1.6%, it is appropriate to take into account the combined elemental effect of tin and silicon on the TCR, which is maintained between -20 ppm / °C and +20 ppm / °C.

[0085] Furthermore, in order to avoid their weakening during the thermal change steps carried out in the method for producing the strips described below from the alloy, the proportion of Si in the resistance alloy of the present invention must be less than 0.15%.

[0086] In fact, the present invention also relates to a method for producing strips of copper-based precision resistance alloys as described above, wherein the elements Mn, Ni, Sn, and selectively Si are composed in the aforementioned proportions, and according to the aforementioned Mn / Ni ratio, the criterion of selectively Si + Sn is introduced, and where applicable, the remaining alloy is copper and unavoidable impurities.

[0087] In a first embodiment of the method of the present invention, the latter includes at least the following steps, which are carried out in order:

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

[0089] - Preferably, the homogenization heat treatment operation should be carried out over a period of 2 to 5 hours, and advantageously at a temperature between 600°C and 800°C;

[0090] - From the ingot homogenized by the aforementioned steps, a strip having a thickness of less than 20 mm is obtained, preferably at a temperature between 700°C and 850°C, with a cross-sectional reduction rate of more than 50%, by dynamic thermal recrystallization including at least rolling, extrusion, or forging;

[0091] - Preferably, a strip having a thickness of less than 10 mm is obtained by static recrystallization after low-temperature curing with a reduction rate between 65% and 85% at a temperature between 550°C and 700°C, preferably over a period of 1 to 3 hours.

[0092] A second embodiment of the method of the present invention includes at least the following steps, performed in order:

[0093] - Melting the constituent elements of the alloy and continuous casting to obtain strips having a thickness of less than 20 mm;

[0094] - Preferably, the homogeneous heat treatment operation should be performed at a temperature between 600°C and 800°C, and preferably for a period between 2 hours and 5 hours;

[0095] - From homogenized strips having a thickness of less than 20 mm, strips having a thickness of less than 10 mm are obtained by static recrystallization after low-temperature curing, preferably at a temperature between 550°C and 700°C, and advantageously over a period of 1 to 3 hours, with a reduction rate between 65% and 85%.

[0096] Due to the specific composition of the precision resistance alloy of the present invention, the method of the present invention advantageously does not require melting and casting in a vacuum chamber.

[0097] In other words, in the method of the present invention, conventional melting and casting are performed, rather than under vacuum.

[0098] Furthermore, implementing this method reduces the heterogeneity in the microstructure that allows for alteration, and ensures the homogeneity and constancy of the electrical properties of the resulting final product.

[0099] It should be noted that the homogenization temperature of the alloy, prior to alteration, not exceeding 800°C, allows for the dissolution of the Sn-rich CuMnSn phase (more than 20% Sn), thus avoiding the melting of these phases, which would likely lead to separation and damage during alteration.

[0100] In preference, when the initial alloy contains silicon in proportions between 0.02% and 0.15%, while adhering to the criterion of Sn + 0.4*Si < 2.0%, preferably < 1.6%, the other constituent elements of the alloy, Cu, Mn, Ni, and Sn, are introduced and melted, and then Si is introduced at the end of the melting process.

Claims

1. A copper (Cu)-based precision resistance alloy for the manufacture of precision resistors, wherein the alloy comprises, by mass%, the following: The manganese (Mn) content is between 20.0% and 23.0%. The nickel (Ni) content is between 4.5% and 8.0%. The proportion of tin (Sn) is between 0.2% and 2.0%. Selectively, the silicon (Si) content is between 0.02% and 0.15%, provided that Sn + 4*Si < 2.0%. The remainder consists of copper and unavoidable impurities. A copper-based precision resistance alloy characterized in that the ratio (mass%) of manganese to nickel is between 3.0 and 5.

0.

2. The copper-based precision resistance alloy according to claim 1, characterized in that the proportion of Sn is between 0.6% and 1.6%.

3. The copper-based precision resistance alloy according to claim 1 or 2, characterized in that the proportion of Mn is between 20.0% and 22.0%.

4. A copper-based precision resistance alloy according to any one of claims 1 to 3, characterized in that the proportion of Ni is between 5.0% and 6.5%.

5. A copper-based precision resistance alloy according to any one of claims 1 to 4, characterized by having a resistance between 70 μΩ. cm and 85 μΩ. cm, a thermoelectric power TEP having a value of less than 2 μV / °C, preferably less than 1 μV / °C, preferably less than 0.5 μV / °C, and a temperature coefficient of resistance TCR between 20°C and 50°C, between -50 ppm / °C and +50 ppm / °C, preferably between -40 ppm / °C and +40 ppm / °C, preferably between -20 and +20 ppm / °C.

6. A method for manufacturing a copper-based resistance alloy strip according to any one of claims 1 to 5, wherein the alloy is, by mass%, It consists of Mn between 20.0% and 23.0%, Ni between 4.5% and 8.0%, Sn between 0.2% and 2.0%, Si selectively between 0.02% and 0.15% satisfying Sn + 4*Si < 2.0%, the remainder being copper and unavoidable impurities. In the alloy, the ratio between the aforementioned proportions of Mn and Ni is between 3.0 and 5.

0. The method described above is characterized by comprising at least the following steps, which are performed in order: - The steps of melting the constituent elements of the alloy and performing semi-continuous casting to obtain an ingot having a thickness or diameter between 100 mm and 250 mm; A homogenization heat treatment operation step of 2 to 5 hours at a temperature between -600°C and 800°C; - From a homogenized ingot, obtain a strip having a thickness of less than 20 mm by dynamic thermal recrystallization, including rolling, extrusion, and forging at a temperature between 700°C and 850°C, with a cross-sectional reduction rate of more than 50%; Step - After low-temperature curing at a temperature between -550°C and 700°C for a period between 1h and 3h with a reduction rate between 65% and 85%, a strip having a thickness of less than 10 mm is obtained by static recrystallization.

7. A method for producing a strip of a copper-based resistance alloy according to any one of claims 1 to 5, wherein the alloy comprises, by mass%, Mn between 20.0% and 23.0%, Ni between 4.5% and 8.0%, Sn between 0.2% and 2.0%, and selectively Si between 0.02% and 0.15%, satisfying Sn + 4 * Si < 2.0%, with the remainder being copper and unavoidable impurities, and the ratio of the aforementioned proportions of Mn to Ni in the alloy being between 3.0 and 5.0, and the method comprises the following: - The steps of melting the constituent elements of the alloy and performing continuous casting to obtain a strip having a thickness of less than 20 mm; A homogenization heat treatment operation step of 2 to 5 hours at a temperature between -600°C and 800°C; - A homogenized strip having a thickness of less than 20 mm is subjected to low-temperature curing at a temperature between 550°C and 700°C for a period between 1 hour and 3 hours with a reduction rate between 65% and 85%, followed by static recrystallization to obtain a strip having a thickness of less than 10 mm.

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