ASTM_D_6208_-_07_2014.pdf

Designation:D620807(Reapproved 2014)Standard Test Method forRepassivation Potential of Aluminum and Its Alloys byGalvanostatic Measurement1This standard is issued under the fixed designation D6208;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last 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 A procedure to determine the repassivation potential ofaluminum alloy 3003-H14(UNSA93003)(1)2as a measure ofrelative susceptibility to pitting corrosion by conducting agalvanostatic polarization is described.Aprocedure that can beused to check experimental technique and instrumentation isdescribed,as well.1.2 The test method serves as a guide for similar measure-ment on other aluminum alloys and metals(2-5).1.3 The values stated in SI units are to be regarded as thestandard.Values given in parentheses are for information only.1.4 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 Standards:3D1193 Specification for Reagent WaterD3585 Specification for ASTM Reference Fluid for CoolantTestsG3 Practice for Conventions Applicable to ElectrochemicalMeasurements in Corrosion TestingG15 Terminology Relating to Corrosion and Corrosion Test-ing(Withdrawn 2010)4G46 Guide for Examination and Evaluation of Pitting Cor-rosionG107 Guide for Formats for Collection and Compilation ofCorrosion Data for Metals for Computerized DatabaseInput3.Terminology3.1 Definitions:Terms used in this test method can be foundin Practice G3 and Terminology G15.3.2 Symbols:3.2.1 EBbreak potential,potential at which the passivealuminum oxide layer breaks down.3.2.2 EGprotection potential as measured in this galvano-static method,potential at which oxide layer repassivates.3.2.3 Jcurrent density,in A/m24.Summary of Test Method4.1 The test method described is an adaptation of themethod described in FORD Motor Company standards(6).4.2 An aluminum alloy specimen is polarized at fixedcurrent density for 20 min.in a solution of coolant andcorrosive water containing chloride.The potential as a functionof time is recorded.4.3 The maximum potential,EBreached upon polarizationis determined,as is the minimum potential following themaximum potential,EG.4.4 Visual examination of the specimen may be made usingGuide G46 as a guide after disassembly and rinsing.5.Significance and Use5.1 This test method is designed to measure the relativeeffectiveness of inhibitors to mitigate pitting corrosion ofaluminum and its alloys,in particular AA3003-H14,rapidlyand reproducibly.The measurements are not intended tocorrelate quantitatively with other test method values or withsusceptibility to localized corrosion of aluminum observed inservice.Qualitative correlation of the measurements and sus-ceptibility in service has been established(1).5.2 Themaximumpotentialreacheduponinitialpolarization,EB,is a measure of the resistance to breakdown ofthe aluminum oxide film.Lower susceptibility to initiation ofpitting corrosion is indicated by a more noble potential(See1This test method is under the jurisdiction of ASTM CommitteeD15 on EngineCoolants and Related Fluids and is the direct responsibility of SubcommitteeD15.06on Glassware Performance Tests.Current edition approved Feb.1,2014.Published March 2014.Originallyapproved in 1997.Last previous edition approved in 2007 as D6208-07.DOI:10.1520/D6208-07R14.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For 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 ASTM website.4The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 Practice G3 and Terminology G15.)This potential,as mea-sured in this test method,is not very sensitive to the inhibitorspresent.5.3 The minimum potential,EG,following the maximumpotential is a measure of the protection against continuedpitting corrosion by the inhibitors.Again,a more noblepotential indicates better protection.This potential is sensitiveto the inhibitors present.5.4 Visual examination of the specimens can provide infor-mation about subleties of the pitting and inhibition mecha-nisms.Number of pits,pit depth,amount of deposit,andsurface discoloration are some examples of recordableobservations,which can assist evaluation of inhibitor effective-ness.5.5 The presence of chloride in the test solution is cr