1、Designation: G69 12Standard Test Method forMeasurement of Corrosion Potentials of Aluminum Alloys1This standard is issued under the fixed designation G69; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of last revision.An
2、umber 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 anaqueous solution of s
3、odium 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. See Practice G193.1.2 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 regulatory
5、 limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodG3 Practice for Conventions Applicable to ElectrochemicalMeasurements in Corrosion TestingG193 Ter
6、minology and Acronyms Relating to Corrosion3. 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 are two ofthe major alloying elements for aluminum, have the greate
7、steffect with copper shifting the potential in the noble or positivedirection, and zinc in the active or negative direction. Forexample, commercially unalloyed aluminum (1100 alloy) has apotential of 750 mV when measured in accordance with thismethod, 2024T3 alloy with nearly all of its nominal 4.3
8、%copper in solid solution, a potential of 600 to 620 mV,depending upon the rate of quenching and 7072 alloy withnearly all of its nominal 1.0 % zinc in solid solution, a potentialof 885 mV (SCE) (1-3).33.2 Because it reflects the amount of certain alloying ele-ments in solid solution, the corrosion
9、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 usesinclude the determination of the effectiveness of solution heattreatment and annealing (1), of the
10、 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 consists of an inert container for the testsolution, a mechanical support for the test specimens
11、 thatinsulates them electrically from each other and from ground, asaturated calomel electrode (SCE), wires and other accessoriesfor electrical connections, and equipment for the measurementof potential. See Note 2.NOTE 2Saturated calomel electrodes are available from severalmanufacturers. It is a g
12、ood 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 3 mV.4.2 High-impedance (1012) voltmeter is suitable for mea-surement of the potential. Measurement of this poten
13、tial should1This test method is under the jurisdiction of ASTM Committee G01 onCorrosion of Metals and is the direct responsibility of Subcommittee G01.11 onElectrochemical Measurements in Corrosion Testing.Current edition approved May 1, 2012. Published October 2012. Originallyapproved in 1981. Las
14、t previous edition approved in 2009 as G6997(2009). DOI:10.1520/G0069-12.2For 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 standards Document Summary page onthe A
15、STM website.3The boldface numbers in parentheses refer to the references at the end of thisstandard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.be carried out to within 6 1 mV. Automatic data recordingsystems may be used to permi
16、t the simultaneous measurementof many specimens and the continuous recording of corrosionpotentials.5. Reagents5.1 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
17、 Analytical Reagents of the American Chemical Society,where such specifications are available.45.2 Purity of WaterThe water shall be distilled or deion-ized conforming to the purity requirements of SpecificationD1193, Type IV reagent water.5.3 Sodium Chloride (NaCl) Analytical Reagent (AR).5.4 Hydro
18、gen 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 less than 20 %hydrogen peroxide be us
19、ed.5.5 Nitric Acid70 % (conc).5.6 Hydrochloric Acid12 N (conc).5.7 Sulfuric Acid36 N (conc).5.8 Sodium Hydroxide.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 resp
20、ect toconcentration of sodium chloride.)6.2 The hydrogen peroxide reagent 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 meas
21、urements.6.5 The total exposed area of all the specimens of the samecomposition 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 unimportantprov
22、ided that the area for measurement is at least 25 mm2, butfor convenience 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 longi
23、s a convenient size.8. Specimen Preparation8.1 Any convenient means, such as sawing or stamping,may be used to prepare a specimen to size provided that it doesnot heat the specimen enough to change its metallurgicalstructure.8.2 Irregular-shaped specimens shall be machined or pre-pared with a coarse
24、 file to provide a reasonably flat surface andto remove nonrepresentative 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
25、lathe file to remove the original mill scale oxide layer.8.3 No filing or 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 clad
26、products with thin claddings which are to be measured.8.4 Mechanical PreparationThe surfaces of all productsselected for measurement, including those with no previouspreparation, are abraded dry with No. 320 grade aluminumoxide or silicon carbide cloth and then with No. 00 steel wool.NOTE 3Caution:
27、Clad products with thin claddings should only beabraded lightly except to remove the cladding for measurement of thecore.8.4.1 Following mechanical preparation, the specimen iscleaned or degreased in an inert solvent (for example, acetone,MEK, EtOH).8.5 Chemical PreparationAnyone of the following fi
28、veprocedures may be used. The etch treatment is followed by arinse in Specification D1193 Type IV water, desmut for oneminute in conc. nitric acid, and final rinse in SpecificationD1193 water and air dry.8.5.1 One minute immersion in HF/HNO3at 93 6 2Ccontaining 5 mL/L of 48% HF and 50 mL/L of concen
29、tratednitric acid. Do not let the HF solution remain in the borosilicateglass vessels used in this method, because the HF solution willattack the glass.8.5.2 One minute in 10% NaOH solution at 71 6 2C.8.5.3 Thirty seconds immersion in 12 N HCL at roomtemperature (22 6 2C).8.5.4 Sixty seconds immersi
30、on in 5N HCl at room tempera-ture (22 6 2C).8.5.5 Five minute immersion in1NH2SO4at 60 6 2C.8.6 Measurement of the core alloy in Alclad alloys requiresremoval of the cladding surfaces. This can be accomplished byeither mechanical or chemical means. It is important that theentire cladding alloy be re
31、moved from one or both sides of theproduct in order to obtain reliable and reproducible results. Thethickness of the Alclad samples should be reduced to at least1.5 times of the total thickness of the clad layer(s) on one orboth sides of the Alclad product. Metallographic cross section-ing may be ne
32、cessary to verify complete removal of thecladding.8.6.1 Mechanical Removal of CladdingSee 8.4.8.6.2 Chemical Removal of CladdingImmerse in 5%NaOH at 60 6 2C for a few minutes. The time of immersionis dependent upon rate of etching and cladding thickness. Rinse4Reagent Chemicals, American Chemical So
33、ciety Specifications, AmericanChemical Society, Washington, DC. For Suggestions on the testing of reagents notlisted by the American Chemical Society, see Annual Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacop
34、eial Convention, Inc. (USPC), Rockville,MD.G69122in cold water, desmut in conc. nitric acid for 1 min, and finalrinse in Specification D1193 Type IV water and air dry.NOTE 4Measure the reduction in thickness of the sheet or platesample to insure complete removal of the cladding.8.7 All parts of a sp
35、ecimen and its electrical connection tobe exposed in the test solution, except for the area of thespecimen prepared 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 corro
36、sion potential measurements, the test speci-mens and the reference electrode are immersed in the appro-priate quantity 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 s
37、hould be taken to ensure that all the unmaskedarea of each test specimen prepared for measurement isexposed to the 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 T
38、he potential of each specimen shall be measured andrecorded with a high impedance voltmeter after 20, 25 and 30min in a 30min run or after 50, 55 and 60 min in a 60minrun.9.4 The 30min potential of each specimen shall be reportedtogether with the average of the last three measurements, thatis, at 20
39、, 25 and 30 min. If the test is continued for 60 min, thepotential at 60 min shall be reported together with the averageof potentials at 50, 55 and 60 min.9.5 Duplicate specimens shall be measured.9.6 The average of the values for duplicate specimens shallbe used if the values agree within 5 mV. If
40、they do not agreewithin 5 mV, at least one additional specimen shall bemeasured. 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.10. Standardization of Test Procedure10.1 The test procedure shall be standar
41、dized 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 acceptable if thevalue obtained is 751 6 20
42、 mV (SCE).11. Report11.1 The following information shall be recorded:11.1.1 Identification of product, alloy, and temper, includingreference to applicable specifications.11.1.2 Whether mechanical or chemical pretreatment wasused; specify which chemical pretreatment.11.1.3 The results of all measurem
43、ents with an indication ofwhether they represent individual values or averages; and ifaverages, also the number of values averaged and the range.12. Precision and Bias512.1 PrecisionThe precision of this test method wasdetermined by analysis of the results of an interlaboratory testprogram with eigh
44、t laboratories participation. PracticeE691was used in the analysis of the data.12.1.1 RepeatabilityThe repeatability, r, (within labora-tory variation) and the repeatability standard deviation (Srweredetermined as in Table 1.12.1.2 ReproducibilityThe reproducibility, R, (betweenlaboratory variation)
45、 and the reproducibility standard deviation(SR) were determined as in Table 2. It should be noted that theapparent cause of the interlaboratory variation was variation ofthe reference electrodes used. The chemical etch treatments of5000 series alloys apparently causes an unstable surface forthis met
46、hod and that is responsible for the larger variation inresults both in repeatability and reproducibility.12.2 BiasThis test method has no bias because thiscorrosion potential is defined only in terms of this test method.13. Keywords13.1 aluminum alloy; aqueous; copper; corrosion potential;sodium chl
47、oride; solid solution; zinc5Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR:G01-1024.TABLE 1 RepeatabilityAlloy Surface Average Sr6r (95 %)1100-H18 Any 759.2 mV 3.0 mV 8.4 mV3003-H18 Any 750.7 mV 3.0 mV 8.4 mV5052-H32 Mech. 756.5
48、 mV 3.0 mV 8.4 mV5052-H32 Chem. 738.4 mV 5.6 mV 15.7 mV2024-T3 Any 605.6 mV 3.0 mV 8.4 mV7075-T6 Any 725.2 mV 3.0 mV 8.4 mVG69123ANNEXES(Mandatory Information)A1. ANALYSIS OF HYDROGEN PEROXIDE REAGENTA1.1 Dilute a sample of the hydrogen peroxide reagent tocontain approximately6gH2O2/L. Then pipet a
49、10-mLaliquotof this solution into a beaker to which has already been added400 mL of water and 15 mL of 50 % sulfuric acid. 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 required to convertgrams per litre of hydrogen peroxide to percent.A1.3 Some stabilizers used with hydrogen peroxide reactwith perman
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