ASTM_G_67_-_13.pdf

Designation:G6713Standard Test Method forDetermining the Susceptibility to Intergranular Corrosion of5XXX Series Aluminum Alloys by Mass Loss After Exposureto Nitric Acid(NAMLT Test)1This standard is issued under the fixed designation G67;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 describes a procedure for constantimmersion intergranular corrosion testing of 5XXX seriesaluminum alloys.1.2 This test method is applicable only to wrought products.1.3 This test method covers type of specimen,specimenpreparation,test environment,and method of exposure.1.4 The values stated in SI units are to be regarded as thestandard.The values given in parentheses are for informationonly.1.5 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 WaterG1 Practice for Preparing,Cleaning,and Evaluating Corro-sion Test Specimens3.Summary of Test Method3.1 This test method consists of immersing test specimensin concentrated nitric acid at 30C(86F)for 24 h anddetermining the mass loss per unit area as a measure ofsusceptibility to intergranular corrosion.4.Significance and Use4.1 This test method provides a quantitative measure of thesusceptibility to intergranular corrosion of Al-Mg and Al-Mg-Mn alloys.The nitric acid dissolves a second phase,analuminum-magnesium intermetallic compound(Al-Mg),inpreference to the solid solution of magnesium in the aluminummatrix.When this compound is precipitated in a relativelycontinuous network along grain boundaries,the effect of thepreferential attack is to corrode around the grains,causingthem to fall away from the specimens.Such dropping out of thegrains causes relatively large mass losses of the order of 25 to75 mg/cm2(160 to 480 mg/in2),whereas,samples ofintergranular-resistant materials lose only about 1 to 15 mg/cm2(10 to 100 mg/in2).When the Al-Mg compound israndomly distributed,the preferential attack can result inintermediate mass losses.Metallographic examination is re-quired in such cases to establish whether or not the loss in massis the result of intergranular attack.4.2 The precipitation of the second phase in the grainboundaries also gives rise to intergranular corrosion when thematerialisexposedtochloride-containingnaturalenvironments,such as seacoast atmospheres or sea water.Theextent to which the alloy will be susceptible to intergranularcorrosion depends upon the degree of precipitate continuity inthe grain boundaries.Visible manifestations of the attack maybe in various forms such as pitting,exfoliation,or stress-corrosion cracking,depending upon the morphology of thegrain structure and the presence of sustained tensile stress.35.Interferences5.1 If all loose particles are not removed during cleaningafter exposure,the mass loss will be low relative to the amountof corrosion that actually occurred.6.Apparatus6.1 Nonmetallic ContainerA suitable inert,nonmetalliccontainer should be used to contain the nitric acid and1This test method is under the jurisdiction of ASTM Committee G01 onCorrosion of Metals and is the direct responsibility of Subcommittee G01.05 onLaboratory Corrosion Tests.This method was developed by a joint task group withThe Aluminum Association,Inc.Current edition approved May 1,2013.Published May 2013.Originallyapproved in 1980.Last previous edition approved in 2004 as G67 04,which waswithdrawn January 2013 and reinstated May 2013.DOI:10.1520/G0067-13.2For 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.3Craig,H.L.Jr.,“Nitric Acid Weight Loss Test for the H116 and H117 Tempersof 5086 and 5456 Aluminum Alloys,”Localized CorrosionCause of MetalFailure,ASTM STP 516,ASTM,1972,pp.1737.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 specimens during the period of the test.The use of individualbeakers for each specimen is recommended;however,theimmersion of multiple specimens in the same container isacceptable.6.1.1 The specimens should be situated in the container sothat none of the major surfaces is in total contact with the wallsof the container.Also,specimens should be isolated electricallyfrom one another.A recommended method of positioning thespecimens is to incline them so that the edges rest on thebottom and side wall of the container.6.1.2 The container shoul