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ASTM A1071 - A 1071M - 11 (2015).pdf

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ASTM A1071 - A 1071M - 11 (2015).pdf

Designation A1071/A1071M − 11 Reapproved 2015Standard Test Method forEvaluating Hygrothermal Corrosion Resistance ofPermanent Magnet Alloys1This standard is issued under the fixed designation A1071/A1071M; the number immediately following the designation indicates theyear of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the equipment, procedures, andmeasurement of the resistance of permanent magnet alloysagainst corrosion in high temperature, high pressure watervapor environments. This test is also known as the BulkCorrosion Test BCT.1.2 The values and equations stated in customary cgs-emuand inch-pound units or SI units are to be regarded separatelyas standard. Within this standard the SI units, when differentfrom customary units, are shown in brackets, the values statedin each system may not be exact equivalents; therefore, eachsystem shall be used independently of the other. Combiningvalues from the two systems may result in nonconformancewith this standard.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-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards2D3330/D3330M Test Method for PeelAdhesion of Pressure-Sensitive Tape2.2 JEDEC Standards3JESD22-A102-C Accelerated Moisture Resistance – Unbi-ased Autoclave3. Terminology3.1 Definitions3.1.1 bulk corrosion test BCT grade, ngrade given toranges of specific weight loss to indicate the relative corrosionresistance of a material. The grades are listed in 15.2.3.1.2 specific weight loss, nweight loss of the specimenper unit of exposed surface area, in units of milligrams persquare centimetre, due to corrosion and disintegration.4. Summary of Test Method4.1 Permanent magnet samples are exposed to pressurizedsteam to determine the resistance of these materials, especiallyrare earth-type permanent magnets, to degradation by thecombined action of heat and water vapor. The resulting weightloss including removed loosely-attached material is used torate the hygrothermal corrosion resistance of the magnet.5. Significance and Use5.1 This test method provides a controlled corrosive envi-ronment which can be utilized to produce relative corrosionresistance information for sintered permanent magnets.5.2 Although prediction of performance in natural environ-ments has seldom been statistically correlated with corrosiontest results, sufficient empirical results are available to supportthe usefulness of this test in quantifying relative resistance tocorrosion from moisture and heat.5.3 The reproducibility of results in this test method isdependent on the type, size, and shape of specimens tested, andthe control of the operating variables. In any testing program,sufficient replicates should be included to establish confidencelimits. Replicates may be run simultaneously, in subsequenttest runs, or in duplicate test chambers.5.4 When multiple test chambers and operators are utilized,efforts shall be made to perform a suitable repeatability andreproducibility study for the equipment, operators, and testmethod.6. Interferences6.1 This test method will not yield meaningful results ifnonhomogeneous specimens such as assemblies or partiallycoated magnets are tested because of the potential aggravatingeffect of galvanic corrosion between dissimilar materials,1This test method is under the jurisdiction of ASTM Committee A06 onMagnetic Properties and is the direct responsibility of Subcommittee A06.01 on TestMethods.Current edition approved Oct. 1, 2015. Published October 2015. Originallyapproved in 2011. Last previous edition approved in 2011 as A1071/A1071M – 11.DOI10.1520/A1071_A1071M–11R15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.3Available from JEDEC Solid State Technology Association, 2500 WilsonBoulevard, Arlington, VA 22201–3834. www.jedec.orgCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1chemical reactivity with included materials, incompletely ex-posed surfaces, and difficulty in determining the amount ofweight loss attributable to the magnet and coating.6.2 Many cleansers contain bleach or chlorides which willincrease the corrosion rate of the samples being tested. Do notuse bleach- or chloride-containing cleansers to clean theinterior of the test chamber or sample racks. Nonmetallicscrubbing pads and water rinsing have been found to besuitable for routine cleaning of chambers and racks.7. Apparatus7.1 AutoclaveAheated pressure chamber capable of main-taining pressurized steam at controlled temperature. The tem-perature shall be maintained within 62C of the selectedtemperature for the duration of the exposure. The atmosphereduring test shall be saturated steam 100 RH. This can beachieved by venting the chamber as it reaches operatingtemperature and pressure and resealing the chamber afterpressure has been reduced to 5 psi [34 kPa] through venting.The escaping steam purges the chamber of air, leaving onlysteam within the chamber. While commercial autoclaves areavailable that have self-contained heaters and timers, a con-ventional pressure cooker with external heater may also beused, as long as temperature and pressure controls capable ofmaintaining suitable control of these variables are present.7.2 BalanceWith suitable holders capable of measuringthe mass of magnetic material to within 60.001 g or 60.1 ofthe magnet’s nominal weight whichever is greater.7.3 Specimen Holders or RacksSuitable containers orracks which can keep specimens from touching each other ormetallic parts of the autoclave chamber. They must be con-structed of material that will not affect the corrosion rate of thesample. Suitable materials of construction have been found tobe aluminum see Note 1, borosilicate or laboratory glass, orhalogen-free polymers.NOTE 1Aluminum readily develops an insulating film when exposedto air or steam. Care should be exercised when using freshly prepared orrefinished aluminum surfaces as the oxide film may be thin enough toallow galvanic corrosion with the magnet under test. Generally, afterexposure to steam, the oxide film is sufficiently thick to prevent galvaniccorrosion.8. Reagents and Materials8.1 Distilled Water.8.2 Masking TapePaper tape with a pressure-sensitiveadhesive with strength of at least 1.57 lb/in. [28 kg/m] whentested in accordance with Procedure A of Test Method D3330/D3330M.8.3 BrushBristle brush made with synthetic polymer ornatural fiber.9. Known Hazards9.1 This test method utilizes equipment operating at el-evated pressure. Suitable means should be employed to ensurethe equipment meets local safety regulations and is in goodoperating condition, particularly regarding the security of thechamber door and ports. Suitable means typically a pressurerelief valve shall be employed to ensure that the pressurewithin the equipment does not exceed its design limit.9.2 This test method utilizes pressurized steam which hasthe ability to cause severe burns. Suitable means should beemployed to ensure that personnel are protected from ventedsteam during operation, and in particular when the chamber isopened at the conclusion of the test.9.3 This test method utilizes elevated temperature. Suitablemeans should be employed to prevent burns caused by theequipment, vented steam, and the specimens.10. Sampling, Test Specimens, and Test Units10.1 A minimum of three replicates should be tested.10.2 Whenever possible the samples should be unmagne-tized. Magnetized samples may be demagnetized electro-magnetically or thermally, provided the thermal process doesnot damage the sample or significantly change its metallurgicalstate. Magnetized samples may be used in the magnetized stateprovided they are secured on the rack so that they do notcontact other samples. Care shall be taken to prevent magneticparticles from being attracted to and sticking to the testsamples, causing erroneous readings. Obtaining accurateweights of magnetic material is difficult on many balances. Formagnetized samples, equipment and techniques that yieldaccurate weights shall be used, including spacing the magnetaway from the mechanism of the balance.11. Preparation of Apparatus11.1 All equipment and specimen holders shall be inspectedand cleaned as necessary prior to use to ensure that the testchamber, support racks, and other components are free ofdebris and visible contamination.12. Calibration and Standardization12.1 Verify calibration of balance and autoclave tempera-ture controller. Verify that autoclave test temperature isoperating within specified range see 7.1.13. Sample Preparation13.1 Test specimens shall not come into direct contact withskin at any point during the procedure due to the potential forskin oils to influence the corrosion rate. Handle the specimenswith gloved hands or clean tools.13.2 Coatings if present or surface debris shall be removedusing nonmetallic scrubbing pads or virgin nonmetallic abra-sive grit blasting. Metallic scrapers or used abrasive grit shallnot be used.13.3 If the specimens must be cleaned with a liquid prior totest, useACS reagent grade, nonpolar organic solvents only; donot use cleansers or bleaches which may influence the corro-sion rate.13.4 Immediately prior to the beginning of the test, thespecimens shall be brushed see 8.3 to remove loosely adheredmaterial. Once sufficiently brushed, the specimens shall be“taped” see 8.2 by repeatedly pressing fresh tape onto thesurface of the specimen until there is no further evidence oftransfer of material from the specimen to fresh tape.A1071/A1071M − 11 2015213.5 Specimen identification shall be accomplished by ameans that does not alter the surface of the specimen, such asmapping the specimen location in the specimen holders, or byfeatures on the specimen holders. Marking the surface of thespecimen with ink, labels, or scribed marks is not permitteddue to potential influence on the corrosion rate. Even when theeffects of marking do not influence the test, if corrosion issubstantial, surface marks are likely to be removed by thetesting.13.6 Immediately prior to referee testing, the specimensshall be dry baked at temperatures between 100 to 122C untila constant weight is achieved after “taping.”14. Procedure14.1 Determine the surface area of each specimen to thenearest 0.05 cm2or with a minimum resolution of 0.1 of thenominal surface area, whichever is greater.14.2 Weigh the specimens prepared as detailed in Section13 to the nearest 0.001 g or 0.1 of the sample weight,whichever is greater.14.3 Place the specimen in the autoclave such that there isample exposure to the test atmosphere and so that contact withcondensed water is minimized.14.4 Expose the specimen to a saturated steam environment100 RH at the required temperature and time duration.Time duration is the cumulative time when the temperature andrelative humidity are at required values. Once the test begins,the total intentional or unintentional interruptions of the testshall not exceed 1 of the total time duration. Standardconditions are 120 6 2C temperature for 96 h. A temperatureof 120C produces a nominal steam pressure of 29 psia[200 kPa]. See Appendix X1 for additional temperature-pressure information. Other conditions see Note 2 may beused if agreed upon by all affected parties.NOTE 2JEDEC JESD22-A102-C lists several time durations that arecommonly used for autoclave testing of electronic components.14.5 At the end of the test, the specimens shall be promptlyremoved from the test chamber, washed or scrubbed in warmtap water, pat dried and allowed to cool to room temperature.Prior to weighing, the specimens shall be brushed to removeloose corrosion products. Once sufficiently brushed, the speci-mens shall be “taped” in the same manner as during samplepreparation.14.6 The specimen shall be weighed to the nearest 0.001 gor 0.1 of the starting magnet weight, whichever is greater.15. Calculation or Interpretation of Results15.1 Calculate the specific weight loss, SWL, in milligramsper square centimetre of exposed surface, by the formulaSWL 51000Wi2 WfA1whereWi the initial weight of specimen, in grams,Wf the final weight of specimen, in grams, andA the total surface area of the specimen, in squarecentimetres.15.2 When specimens were exposed to the standard testconditions in accordance with 14.4, the BCT grade is definedby the following table based on the specific weight lossrounded as follows. For weight loss less than 10 mg/cm2, roundto the nearest 0.1; for weight loss equal to or higher than 10,round to the nearest whole numberBCT Grade Specific Weight Lossmg/cm2A 1.0B 1.1 to 3.9C 4.0 to 10D 11to20E 21to35F 36 or more16. Report16.1 Report the following data for each test performed16.1.1 Specimen identification, including identity of themagnet material and any lot-specific notes.16.1.2 Condition of the specimens, including whether thesamples were magnetized, nonmagnetized, or demagnetizedincluding method of demagnetization; and whether thesamples were previously coated including method of coatingremoval.16.1.3 Temperature, pressure, and duration of test.16.1.4 The BCT grade if the standard test conditions wereused, or the average weight loss in mg/cm2of exposuresurface area, or both.16.1.5 Report results for each specimen.17. Precision and Bias17.1 Because the repeatability and reproducibility of the testmethod is significantly influenced by the specific characteris-tics of the test specimens, it is not considered possible to statemeaningful values for repeatability and reproducibility that areuniversally applicable.17.2 Since there is no accepted reference material fordetermining the bias for the procedure in this test method, biashas not been determined.18. Keywords18.1 autoclave; BCT; bulk corrosion test; corrosion resis-tance; hygrothermal; permanent magnetA1071/A1071M − 11 20153APPENDIXNonmandatory InformationX1. APPENDIXX1.1 Autoclave TestAn autoclave is a sealed vessel ca-pable of being raised to greater than atmospheric pressurethrough the application of a gas or vapor. For the purposes ofthis test, the atmosphere is steam obtained by heating water ina closed vessel. Under these conditions, the relationshipbetween temperature and pressure has been well establishedand the information, called “steam tables,” is published innumerous places. The chart in

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