1、Designation: A712 07 (Reapproved 2013)Standard Test Method forElectrical Resistivity of Soft Magnetic Alloys1This standard is issued under the fixed designation A712; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、 revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the measurement of electricalresistivity of strip or bar specimens of soft magnetic alloys.1.2 The
3、 values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priat
4、e safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A34/A34M Practice for Sampling and Procurement Testingof Magnetic Materials3. Summary of Test Method3.1 The electrical resistance of a 0.25-m long (minimum
5、)test specimen is measured with a Kelvin-type resistance bridgeor a digital multimeter or the potentiometer-ammeter method.The resistivity is then calculated from the resistance measure-ment and the dimensions of the specimen and is known as theelectrical resistivity of the material. This value is e
6、qual to theresistance between opposite faces of a cube of unit dimensions.4. Significance and Use4.1 This test method is suitable for the measurement of theelectrical resistivity of specimens of soft magnetic materials.4.2 The reproducibility and repeatability of this test methodare such that it is
7、suitable for design, specification acceptance,service evaluation, quality assurance, and research and devel-opment.5. Apparatus5.1 Kelvin-type resistance bridge or a digital multimeter ora dc potentiometer and dc ammeter providing resistancemeasurements to an accuracy within 0.5 % of the accepted tr
8、uevalue.6. Sampling6.1 Samples shall be representative of the material in thephysical condition as shipped or agreed upon by the producerand the user.7. Test Specimen7.1 The test specimen shall be a straight strip or bar or wireof substantially uniform cross-sectional area.7.2 It shall have a minimu
9、m length of 0.25 m. Stripspecimens preferably should have a uniform width of 0.03 mminimum, unless not available.7.2.1 If width of the strip material to be sampled preventsobtaining a sample of 0.03-m minimum width, the specimenwidth to be used shall be the maximum obtainable and shall beagreed upon
10、 between the producer and the user.7.2.2 Bars and wires having circular, rectangular, or othersections shall be used in the sectional dimensions as produced,unless they are so large as to require cutting a representativesample of suitable dimensions.7.3 It shall be free of obvious surface defects.7.
11、4 The surface shall be cleaned by wiping with a cloth. Oiland grease, if present on the surface, shall be removed with asuitable solvent. Normal surface oxide or core plating need notbe removed except in areas in which it is necessary to makesatisfactory electrical contact.8. Procedure8.1 Measure th
12、e electrical resistance of the test specimenusing a Kelvin-type resistance bridge or a digital multimeter orpotentiometer-ammeter system having separate current andpotential leads.8.2 The distance between each potential lead contact and thecorresponding current lead contact shall be at least twice t
13、hewidth of the test specimen with the two potential contacts lyingbetween the current contacts. The distance between the poten-tial contacts shall be not less than 0.12 m.1This test method is under the jurisdiction of ASTM Committee A06 onMagnetic Properties and is the direct responsibility of Subco
14、mmittee A06.01 on TestMethods.Current edition approved May 1, 2013. Published July 2013. Originally approvedin 1975. Last previous edition approved in 2007 as A71207. DOI: 10.1520/A0712-07R13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at ser
15、viceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States18.3 The dimension of each potential contact in the dire
16、ctionof the length of the specimen shall be not more than 0.5 % ofthe distance between potential contacts.8.4 The contacts to the specimen shall be located centrallywith respect to the specimens width dimension, and thecurrent contacts shall cover more than 80 % of the width. Areliable contact shall
17、 be made with the specimen by both thecurrent and potential leads.8.5 Specimen temperature during test should be about 25C.8.6 To eliminate errors as a result of contact potential, taketwo readings, one direct and one with the current reversed, inclose succession.8.7 The electrical current in the te
18、st specimen must belimited to avoid overheating but must be adequate to providesufficient sensitivity to show an out-of-balance condition whenthe resistance reading is changed 0.5 % of the value recorded.If the current is too low, sensitivity is low also, and a balancecan be shown for a broad range
19、of resistance.9. Calculation9.1 Strip Specimens:9.1.1 Determine the average cross-sectional area of the testspecimen from the weight, length, and density as follows:A 5 m/l (1)where:A = cross-sectional area of test specimen, m2;m = mass of test specimen, kg;l = length of test specimen, m; and = dens
20、ity of test specimen, kg/m3, determined in accor-dance with Practice A34/A34M.9.1.2 Eq 1 assumes a negligible mass of any coatingmaterial.9.2 Bar and Wire SpecimensThe cross-sectional area ofthe test specimen shall be based on direct measurements witha micrometer or caliper.9.3 Calculate resistivity
21、 from the measured value of electri-cal resistance and the cross-sectional area as follows: 5 RA/l2(2)where: = electrical resistivity of the material, m;R = resistance of electrical path, ;A = cross-sectional area of electrical path, m2; andl2= length of electrical path between potential contacts on
22、the test specimen, m.9.4 The resistivity units in ohm-metres shown in Eq 2 canbe converted to microhm-centimetres by multiplying the ohm-metre figure by 108microhm-centimetres per ohm-metre. Forexample, if the resistivity is 0.25 106 m; 0.25 106108 cm/ m is equal to 25 cm.NOTE 1The resistivities of
23、commercial soft magnetic alloys areshown in Annex A1.10. Precision and Bias10.1 Although no rigorous interlaboratory comparisons ofthis test method have been performed, it is estimated that thereproducibility standard deviation is no greater than 2 % of themean.10.2 The bias of this test method is b
24、elieved to be zero.11. Keywords11.1 electrical resistivity; magnetic alloy; potentiometer-ammeter; resistance bridgeANNEX(Mandatory Information)A1. RESISTIVITIESA1.1 This test method assumes the establishment of auniform current density along the test specimen throughout theregion between the potent
25、ial contacts. The current contactsshould be in the form of transverse clamps covering at least80 % and preferably the entire width of the specimen. Thepotential contacts can be either knife edge or point contacts.A1.1.1 If a potentiometer is used, a suitable dc source andammeter are required to esta
26、blish and measure the total currentin the specimen, which should be limited to avoid excessiveheating. The required R is then the ratio of the measuredpotential drop to the measured current. When the potentiometeris balanced, no current flows in the potential leads so that anycontact resistance at t
27、he potential points is of no consequence.A1.1.2 The Kelvin bridge is calibrated to read directly theresistance between the potential points without knowledge ofthe current in the specimen. Contact resistance at the potentialpoints and the resistance of the four leads to the specimen arenot a part of
28、 the required R and are usually negligible portionsof the corresponding components of the bridge system.A1.1.3 Digital multimeters used for measuring resistance inthe range required for this test method will be equipped forfour-wire ohm measurements. In the four-wire method, acontrolled source curre
29、nt is applied to the resistance to bemeasured via the current leads, and the voltage drop is sensedacross the potential (or sense) leads. Since the input resistanceof the digital multimeter is very large (typically greater than 10A712 07 (2013)2M), the contact resistance between the sense leads and
30、thespecimen and the resistance of the leads do not affect themeasurement.A1.2 Typical resistivities of iron-silicon-aluminum alloysteel sheets are shown in Fig. A1.1 and other soft magneticalloys in Table A1.1. Commercial electrical steels are low-carbon, silicon-iron, or silicon-aluminum-iron alloy
31、s contain-ing up to 3.5 % silicon and only a small amount of aluminum.NOTE 1The linear equation for the graph in this figure is as follows: = 0.1325 106+ 0.113 (percent silicon + percent aluminum) 106 mwhere = electrical resistivity in ohm-metres at approximately 25C. The equation is based on the av
32、erage line drawn through many test points obtainedon commercial grades of electrical steels of various compositions. Individual tests may show departures from the average line, which is shown in equationand graphical form for general use and guidance. The intercept constant 0.1325 applies only to st
33、eels having alloying elements over about 0.15 %. Asthe percentage of alloying elements decreases to low values, the intercept constant decreases, approaching the value of about 0.107.FIG. A1.1 Electrical Resistivities Versus Composition of Commercial Grades of Electrical SteelsA712 07 (2013)3ASTM In
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35、ly their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand s
36、hould be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on S
37、tandards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 6
38、10-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).TABLE A1.1 Electrical Resistivity of Soft Magnetic Alloys of Nickel, Chromi
39、um, and IronGeneral CompositionTypical ElectricalResistivity, mGeneral Name36 % Nickel, balance iron 0.82 106Invar45 % Nickel, balance iron 0.53 45 Permalloy48 % Nickel, balance iron 0.48 High Perm, 49; 475052 % Nickel, balance iron 0.43 52 Alloy65 % Nickel, balance iron 0.22 65 Permalloy77 % Nickel
40、, 5 % copper, 2.6 % chromium,balance iron0.60 Mumetal78.5 % Nickel, balance iron 0.16 78 Permalloy80 % Nickel, 4 % molybdenum, balance iron 0.58 479 Permalloy; Hy Mu 8080 % Nickel, 5 % molybdenum, balance iron 0.60 579 Permalloy; Hy Mu 800 Supermalloy17 % Chromium, balance iron 0.61 Stainless Type 430A712 07 (2013)4
