ASTM_G_69_-_12.pdf

Designation:G6912Standard 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.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 anaqueous solution of sodium chloride with enough hydrogenperoxide added to provide an ample supply of cathodicreactant.NOTE1The 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 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 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 Terminology 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 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)has apotential of 750 mV when measured in accordance with thismethod,2024T3 alloy with nearly all of its nominal 4.3%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 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 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 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.NOTE2Saturated 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 3 mV.4.2 High-impedance(1012)voltmeter is suitable for mea-surement of the potential.Measurement of this potential shouldbe carried out to within 6 1 mV.Automatic data recordingsystems may be used to permit 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 that1This 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.Last 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 ASTM website.3The boldface numbers in parentheses refer to the references at the end of thisstandard.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 all reagents shall conform to the specifications of the Commit-tee on 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 R