1、Designation: G 69 97 (Reapproved 2009)Standard Test Method forMeasurement of Corrosion Potentials of Aluminum Alloys1This standard is issued under the fixed designation G 69; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year
2、 of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers a procedure for measurement ofthe corrosion potential (see Note 1) of an aluminum alloy in ana
3、queous solution of sodium chloride with enough hydrogenperoxide added to provide an ample supply of cathodicreactant.NOTE 1The corrosion potential is sometimes referred to as theopen-circuit solution or rest potential.1.2 The values stated in SI units are to be regarded asstandard. No other units of
4、 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-priate safety and health practices and determine the applica-bility of regulator
5、y limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 1193 Specification for Reagent Water3. Significance and Use3.1 The corrosion potential of an aluminum alloy dependsupon the amounts of certain alloying elements that the alloycontains in solid solution. Copper and zinc, which ar
6、e two ofthe major alloying elements for aluminum, have the greatesteffect with copper shifting the potential in the noble or positivedirection, and zinc in the active or negative direction. Forexample, commercially unalloyed aluminum (1100 alloy)3hasa potential of 750 mV when measured in accordance
7、with thispractice, 2024T3 alloy with nearly all of its nominal 4.3 %copper in solid solution, a potential of 600 to 620 mV (Note2), and 7072 alloy with nearly all of its nominal 1.0 % zinc insolid solution, a potential of 885 mV (SCE) (1-3).4NOTE 2The potential depends upon the rate of quenching.3.2
8、 Because it reflects the amount of certain alloying ele-ments in solid solution, the corrosion potential is a useful toolfor characterizing the metallurgical condition of aluminumalloys, especially those of the 2XXX and 7XXX types, whichcontain copper and zinc as major alloying elements. Its usesinc
9、lude the determination of the effectiveness of solution heattreatment and annealing (1), of the extent of precipitationduring artificial aging (4) and welding (5), and of the extent ofdiffusion of alloying elements from the core into the claddingof alclad products (2).4. Apparatus4.1 The apparatus c
10、onsists of an inert container for the testsolution, a mechanical support for the test specimens thatinsulates them electrically from each other and from ground,saturated calomel electrode (SCE) (see Note 3), wires andaccessories for electrical connections, and equipment for themeasurement of potenti
11、al.NOTE 3Saturated calomel electrodes are available from severalmanufacturers. It is a good practice to ensure the proper functioning of thereference electrode by measuring its potential against one or morereference electrodes. The potential difference should not exceed 2 or 3mV.54.2 A high-impedenc
12、e (1012V) voltmeter is suitable formeasurement of the potential. Measurement of this potentialshould be carried out to within 6 1 mV. Automatic datarecording systems may be used to permit the simultaneousmeasurement of many specimens and the continuous recordingof corrosion potentials.5. Reagents5.1
13、 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the American Chemical Society,1This test method is under the jurisdiction of ASTM Committe
14、e G01 onCorrosion of Metals and is the direct responsibility of Subcommittee G01.11 onElectrochemical Measurements in Corrosion Testing.Current edition approved May 1, 2009. Published May 2009. Originallyapproved in 1981. Last previous edition approved in 2003 as G 6997(2003).2For referenced ASTM st
15、andards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3All alloy designations are those of the Aluminum Association.4The boldface numbers
16、in parentheses refer to the references at the end of thisstandard.5Round-robin test conducted by G01.11 (unpublished results).1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.where such specifications are available.6Other grades may b
17、eused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.5.2 Purity of WaterThe water shall be distilled or deion-ized conforming to the purity requirements of SpecificationD 1193, Type IV reagent wate
18、r.5.3 Sodium Chloride (NaCl).5.4 Hydrogen Peroxide (H2O2) (30 %)In case of uncer-tainty (for example, whenever freshly opened reagent is notused), the concentration of hydrogen peroxide in the reagentshall be confirmed by chemical analysis as described in AnnexA1. In no case shall reagent containing
19、 less than 20 %hydrogen peroxide be used.6. Solution Conditions6.1 The test solution shall consist of 58.5 6 0.1 g of NaCland 9 6 1 mL of 30 % hydrogen peroxide reagent per 1 L ofaqueous solution. (This solution is 1 M with respect toconcentration of sodium chloride.)6.2 The hydrogen peroxide reagen
20、t shall be added justbefore measurements are made because it decomposes uponstanding.6.3 Freshly prepared solution shall be used for each set ofmeasurements.6.4 Not less than 500 mL of solution shall be used for eachset of measurements.6.5 The total exposed area of all the specimens of the samecompo
21、sition in each set of measurements shall not exceed 100mm2per 100 mL of solution.6.6 The temperature of the test solution shall be maintainedat 25 6 2C.7. Test Specimen7.1 For measurement alone, specimen size is unimportantprovided that the area for measurement is at least 25 mm2, butfor convenience
22、 the specimen, wherever possible, should belarge enough to permit ease of handling during preparation andan electrical connection outside the test solution. A specimen afew millimetres thick by about 15 mm wide and 100 mm longis a convenient size.8. Specimen Preparation8.1 Any convenient means such
23、as sawing or stamping maybe used to prepare a specimen to size provided that it does notheat the specimen enough to change its metallurgical structure.8.2 Irregular-shaped specimens shall be machined or pre-pared with a coarse file to provide a reasonably flat surface andto remove nonrepresentative
24、metal (for example, affected bysawing or stamping, or in case of clad product where core is tobe measured). Further preparation consists of filing with a longlathe file. Original flat surface specimens are also filed withlong lathe file to remove the original mill scale oxide layer.8.3 No filing or
25、machining is needed to prepare specimensthat have original flat surface, representative of its metallurgi-cal structure, or to prepare specimens that are too thin to permitmore than minimal removal of metal; these include cladproducts with thin claddings which are to be measured.8.4 The surfaces of
26、all products selected for measurement,including those with no previous preparation, are abraded drywith No. 320 grade aluminum oxide or silicon carbide clothand then with No. 00 steel wool.NOTE 4Caution: Clad products with thin claddings should only beabraded lightly except to remove the cladding fo
27、r measurement of thecore.8.5 Following mechanical preparation, the specimen iscleaned, or degreased, in an inert solvent (for example, acetoneor perchloroethylene).8.6 All parts of a specimen and its electrical connection tobe exposed in the test solution, except for the area of thespecimen prepared
28、 for measurement, are masked off. Anymaterial that masks a surface physically and electrically andthat is inert in the test solution may be used (see Annex A2).9. Procedure9.1 For corrosion potential measurements, the test speci-mens and the reference electrode are immersed in the appro-priate quant
29、ity of test solution; the test specimens are con-nected to the positive terminal of the equipment for measuringpotential, and the reference electrode to the negative terminal.9.2 Care should be taken to ensure that all the unmaskedarea of each test specimen prepared for measurement isexposed to the
30、test solution and that any other unmasked areais not exposed. Care should also be taken to ensure that anyunmasked portion of the electrical connection is outside the testsolution.9.3 The potential of each specimen shall be measured at5-min intervals for a period of1horrecorded continuouslyusing the
31、 output of a high-impedance voltmeter.9.4 The potential of each specimen shall be reported as theaverage of the values for the last 30 min of measurement (thatis, for the last 7 measurements).9.5 Duplicate specimens shall be measured.9.6 The average of the values for duplicate specimens shallbe used
32、 if the values agree within 5 mV. If they do not agreewithin 5 mV at least one additional specimen shall be mea-sured. The values for the three or more specimens shall beaveraged if they agree within 10 mV but they shall be reportedindividually if they do not agree.10. Standardization of Test Proced
33、ure10.1 The test procedure shall be standardized by measure-ment of the free corrosion potential of a sample of commer-cially produced 3003 alloy sheet. Sheet of any temper issuitable because the potential of this product is not affectedsignificantly by temper.10.2 The procedure shall be considered
34、acceptable if thevalue obtained is 748 6 11 mV (SCE).6Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd.,
35、 Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,MD.G 69 97 (2009)211. Report11.1 The following information shall be recorded:11.1.1 Identification of product, alloy, and temper includingreference to applicable spe
36、cifications.11.1.2 The results of all measurements with an indication ofwhether they represent individual values or averages; and ifaverages, also the number of values averaged.12. Precision and Bias712.1 PrecisionThe precision of this test method wasdetermined by the statistical examination of the
37、interlaboratorytest results.12.1.1 RepeatabilityThe repeatability (within laboratoryvariability) standard deviation (Srand the 95 % limit (r = 2.8Sr) was determined for two alloys as follows:Alloy Average Srr(95 %)1100-H18 758 mV 0.0018 65.1 mV3003-H18 748 mV 0.0017 64.7 mV12.1.2 ReproducibilityThe
38、reproducibility (between labo-ratory variability) standard deviation (SR) and the 95 % limit(R = 2.8 SR) was determined for two alloys as follows:Alloy Average SRR(95 %)1100-H18 758 mV 0.0018 612 mV3003-H18 748 mV 0.0017 611 mV12.2 BiasNo information can be presented on the bias ofthe procedure in t
39、his test method because no accepted externalreference value is available. The values for corrosion potentialof aluminum alloys as measured by this test method are definedonly in terms of this test method.13. Keywords13.1 aluminum alloy; aqueous; copper; corrosion potential;sodium chloride; solid sol
40、ution; zincANNEXES(Mandatory Information)A1. ANALYSIS OF HYDROGEN PEROXIDE REAGENTA1.1 Dilute a sample of the hydrogen peroxide reagent tocontain approximately6gH2O2/L. Then pipet a 10-mLaliquotof this solution into a beaker to which has already been added400 mL of water and 15 mL of 50 % sulfuric a
41、cid. Titrate thissolution with standard 0.1 N potassium permanganate solution.A1.2 To obtain the grams of hydrogen peroxide per litre ofreagent, multiply the millilitres of potassium permanganatesolution used by 0.1 times 0.017 times the aliquot factor.Tablesin chemical handbooks provide the data re
42、quired to convertgrams per litre of hydrogen peroxide to percent.A1.3 Some stabilizers used with hydrogen peroxide reactwith permanganate, but this interference can be ignored when-ever the analysis given by the manufacturer was also deter-mined by permanganate analysis.A2. MASKING MATERIALSA2.1 Mat
43、erials suitable for masking are made by severalmanufacturers.A2.2 A satisfactory masking material can be prepared byadding powdered rosin gradually to melted beeswax untilsaturation is obtained. Several hours may be required becauseof the slow rate of dissolution of the rosin.APPENDIX(Nonmandatory I
44、nformation)X1. CONVERSION FACTORS FOR POTENTIALSX1.1 Many corrosion potentials of aluminum alloys in theliterature were measured in an aqueous solution at 25Ccontaining 53 g of NaCl and 9 mL of 30 % H2O2/L. Thepotentials were measured with a 0.1 N calomel electrode withits tip immersed directly into
45、 the solution without bridging.X1.2 To a good approximation, values measured underX1.1 may be converted to those measured by this practicebythe addition of 92 mV (for example, 830 mV convertsto 738 mV).X1.3 Alternatively, values measured by this practice maybe converted to those measured under X1.1
46、by the subtractionof 92 mV (for example, 738 mV converts to 830 mV).7Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR: G011015.G 69 97 (2009)3REFERENCES(1) Brown, R. H., Fink, W. L., and Hunter, M. S., “Measurement ofIrreversible
47、Potentials as a Metallurgical Research Tool,” Transac-tions of the American Institute of Mining and Metallurgical Engineers,Institute of Metals Division, Vol 143, 1941, pp. 115123.(2) Brown, R. H., “Aluminum Alloy Laminates: Alclad and Clad Alumi-num Alloy Products,” Chapter 11 in Composite Engineer
48、ing Lami-nates, G. H. Dietz(editor), MIT Press, Cambridge, MA, 1969.(3) Anderson, W.A., and Stupf, H. C., Corrosion Magazine, Vol 6, 1980,p. 212.(4) Lifka, B. W., and Sprowls, D. O., “Significance of IntergranularCorrosion in High Strength Aluminum Alloys,” Symposium on Local-ized CorrosionCause of
49、Metal Failure, ASTM STP 516, Am. Soc.Testing Mats., 1972, pp. 12044.(5) Shumaker, M. B., Kelsey, R.A., Sprowls, D. O., and Williamson, J. G.,“Evaluation of Various Techniques for Stress Corrosion TestingWelded Aluminum Alloys,” Symposium on Stress Corrosion Testing,ASTM STP 425, Am. Soc. Testing Mats., 1967, pp. 31741.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any su
