ASTM_G_64_-_99_2013.pdf

Designation:G6499(Reapproved 2013)Standard Classification ofResistance to Stress-Corrosion Cracking of Heat-TreatableAluminum Alloys1This standard is issued under the fixed designation G64;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.INTRODUCTIONStress corrosion behavior is an important characteristic to be considered when optimizing the choiceof material for an engineering structure.Unfortunately,there is no generally accepted scale formeasuring it,and stress corrosion tendencies are difficult to define because of the complexinterdependence of the material,tensile stress,environment,and time.Conventional test-dependenttypes of laboratory stress corrosion data have only very limited applicability in mathematical modelsused for materials selection.This standard is intended to provide a qualitative classification of the relative resistance to stresscorrosion cracking(SCC)of high-strength aluminum alloys to assist in the selection of materials.Theclassification is based on a combination of service experience and a widely accepted laboratorycorrosion test.It is cautioned,however,that any such generalized classification of alloys can involve anoversimplification in regard to their behavior in unusual environments.Moreover,the quantitativeprediction of the service performance of a material in a specific situation is outside the scope of thisstandard.1.Scope1.1 This classification covers alphabetical ratings of therelative resistance to SCC of various mill product forms of thewrought 2XXX,6XXX,and 7XXX series heat-treated alumi-num alloys and the procedure for determining the ratings.1.2 The ratings do not apply to metal in which the metal-lurgical structure has been altered by welding,forming,orother fabrication processes.1.3 The values stated in SI units are to be regarded as thestandard.The values given in parentheses are for informationonly.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:2G44 Practice for Exposure of Metals andAlloys byAlternateImmersion in Neutral 3.5%Sodium Chloride Solution2G47 Test Method for Determining Susceptibility to Stress-Corrosion Cracking of 2XXX and 7XXX AluminumAlloy Products2.2 Other Documents:MIL-HANDBOOK-5 Metallic Materials and Elements forAerospace Vehicle Structures3MIL-STD-1568 Materials and Processes for Corrosion Pre-vention and Control in Aerospace Systems31This classification is under the jurisdiction of ASTM Committee G01 onCorrosion of Metals and is the direct responsibility of Subcommittee G01.06 onEnvironmentally Assisted Cracking.Current edition approved May 1,2013.Published July 2013.Originally approvedin 1980.Last previous edition approved in 2005 as G64 99(2005).DOI:10.1520/G0064-99R13.2For 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.3Available from Standardization Documents Order Desk,DODSSP,Bldg.4,Section D,700 Robbins Ave.,Philadelphia,PA 19111-5098Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 MSFC-SPEC-522A Design Criteria for Controlling StressCorrosion Cracking43.Terminology3.1 Definitions:3.1.1 lotan identifiable quantity of material of the samemill form,alloy,temper,section,and size(or thickness,in thecase of sheet and plate)traceable to a heat treat lot or lots,andsubjected to inspection at one time.3.1.2 stress-corrosion cracking(SCC)a cracking processthat requires the simultaneous action of a corrodent andsustained tensile stress.SCC in aluminum alloy productshistorically has been observed to follow an intergranular pathleading to the ultimate fracture.Thus,for the purpose of thisstandard,a fractured test specimen that reveals only pittingcorrosion or pitting plus transgranular cracking shall not beconsidered as an SCC failure(Test Method G47).4.Significance and Use4.1 This classification involves alphabetical ratings intendedonly to provide a qualitative guide for materials selection.Theratings are based primarily on the results of standard corrosiontests.4.2 Interpretations of the SCC ratings in terms of typicalproblem areas including service experience are given in Table1.Practical experience has shown that SCC problems withaluminum alloys generally have involved situations where thedirection and magnitude of the tensile stresses resulting frommanufacturing or use,or both,of the material wer