ASTM G64-99(2013)

Standard Classification of Resistance to Stress-Corrosion Cracking of Heat-Treatable Aluminum Alloys

SIGNIFICANCE AND USE
4.1 This classification involves alphabetical ratings intended only to provide a qualitative guide for materials selection. The ratings are based primarily on the results of standard corrosion tests.  
4.2 Interpretations of the SCC ratings in terms of typical problem areas including service experience are given in Table 1. Practical experience has shown that SCC problems with aluminum alloys generally have involved situations where the direction and magnitude of the tensile stresses resulting from manufacturing or use, or both, of the material were not recognized.Note 1—The stress levels mentioned below and the test stresses mentioned in 6.2 are not to be interpreted as “threshold” stresses, and are not recommended for design. Other documents, such as MIL-HANDBOOK-5, MIL-STD-1568, NASC SD-24, and MSFC-SPEC-522A, should be consulted for design recommendations.  
4.3 A list of the SCC ratings for the heat-treatable aluminum alloy products is given in Table 2. Revisions to the table will be required as new materials become available and additional test results are accumulated.
4.4 These alphabetical ratings are not suitable for direct use in mathematical models for material selection, but numerical weights and confidence factors can be devised on the basis of experience and judgment of the materials engineer.5
SCOPE
1.1 This classification covers alphabetical ratings of the relative resistance to SCC of various mill product forms of the wrought 2XXX, 6XXX, and 7XXX series heat-treated aluminum alloys and the procedure for determining the ratings.  
1.2 The ratings do not apply to metal in which the metallurgical structure has been altered by welding, forming, or other fabrication processes.  
1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.  
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 30-Apr-2013
• ICS: 77.120.10 - Aluminium and aluminium alloys
• Technical Committee: G01 - Corrosion of Metals
• Drafting Committee: G01.06 - Environmentally Assisted Cracking

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:G64 −99 (Reapproved 2013)
Standard Classification of
Resistance to Stress-Corrosion Cracking of Heat-Treatable
Aluminum Alloys
ThisstandardisissuedunderthefixeddesignationG64;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Stresscorrosionbehaviorisanimportantcharacteristictobeconsideredwhenoptimizingthechoice
of material for an engineering structure. Unfortunately, there is no generally accepted scale for
measuring it, and stress corrosion tendencies are difficult to define because of the complex
interdependence of the material, tensile stress, environment, and time. Conventional test-dependent
types of laboratory stress corrosion data have only very limited applicability in mathematical models
used for materials selection.
This standard is intended to provide a qualitative classification of the relative resistance to stress
corrosion cracking (SCC) of high-strength aluminum alloys to assist in the selection of materials. The
classification is based on a combination of service experience and a widely accepted laboratory
corrosion test.
It is cautioned, however, that any such generalized classification of alloys can involve an
oversimplification in regard to their behavior in unusual environments. Moreover, the quantitative
prediction of the service performance of a material in a specific situation is outside the scope of this
standard.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This classification covers alphabetical ratings of the
G44 PracticeforExposureofMetalsandAlloysbyAlternate
relative resistance to SCC of various mill product forms of the
Immersion in Neutral 3.5 % Sodium Chloride Solution
wrought 2XXX, 6XXX, and 7XXX series heat-treated alumi-
G47 Test Method for Determining Susceptibility to Stress-
num alloys and the procedure for determining the ratings.
Corrosion Cracking of 2XXX and 7XXX Aluminum
1.2 The ratings do not apply to metal in which the metal- Alloy Products
lurgical structure has been altered by welding, forming, or
2.2 Other Documents:
other fabrication processes.
MIL-HANDBOOK-5 Metallic Materials and Elements for
Aerospace Vehicle Structures
1.3 The values stated in SI units are to be regarded as the
MIL-STD-1568 Materials and Processes for Corrosion Pre-
standard. The values given in parentheses are for information
vention and Control in Aerospace Systems
only.
MSFC-SPEC-522A Design Criteria for Controlling Stress
Corrosion Cracking
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3. Terminology
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
3.1 Definitions:
bility of regulatory limitations prior to use.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
This classification is under the jurisdiction of ASTM Committee G01 on Standards volume information, refer to the standard’s Document Summary page on
Corrosion of Metals and is the direct responsibility of Subcommittee G01.06 on the ASTM website.
Environmentally Assisted Cracking. Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,
CurrenteditionapprovedMay1,2013.PublishedJuly2013.Originallyapproved Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098
in 1980. Last previous edition approved in 2005 as G64 – 99 (2005). DOI: Available from NationalAeronautics and SpaceAdministration (NASA), 300 E
10.1520/G0064-99R13. St. SW, Washington, D.C.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G64−99 (2013)
TABLE 1 Practical Interpretation of Ratings for Resistance to SCC
NOTE 1—The stress levels mentioned below and the test stresses mentioned in 6.2 are not to be interpreted as “threshold” stresses, and are not
recommended for design. Other documents, such as MIL-HANDBOOK-5, MIL-STD-1568, NASC SD-24, and MSFC-SPEC-522A, should be consulted
for design recommendations.
Rating Interpretation
A
A Very high. SCC not anticipated in general applications if the total sustained tensile stress is less than 75 % of the minimum specified yield strength for
the alloy, heat treatment, product form, and orientation.
A
B High. SCC not anticipated if the total sustained tensile stress is less than 50 % of the minimum specified yield strength.
A
C Intermediate. SCC not anticipated if the total sustained tensile stress is less than 25 % of the minimum specified yield strength. This rating is designated
for the short transverse direction in improved products used primarily for high resistance to exfoliation corrosion in relatively thin structures where appre-
ciable short transverse stresses are unlikely.
A
D Low. SCC failures have occurred in service or would be anticipated if there is any sustained tensile stress in the designated test direction. This rating cur-
rently is designated only for the short transverse direction in certain materials.
A
The sum of all stresses including those from service loads (applied), heat treatment, straightening, forming, and so forth.
3.1.1 lot—an identifiable quantity of material of the same chosen for the laboratory test because it is widely used for
mill form, alloy, temper, section, and size (or thickness, in the aluminum alloys and is capable of detecting materials that
case of sheet and plate) traceable to a heat treat lot or lots, and would be likely to be susceptible to SCC in natural environ-
subjected to inspection at one time. ments.
3.1.2 stress-corrosion cracking (SCC)—a cracking process
5.2 Other types of tests using precracked specimens or
that requires the simultaneous action of a corrodent and
dynamic loading have promise as alternative or supplemen-
sustained tensile stress. SCC in aluminum alloy products
tary methods, but they presently require better understanding
historically has been observed to follow an intergranular path
and standardization.
leading to the ultimate fracture. Thus, for the purpose of this
standard, a fractured test specimen that reveals only pitting 6. Test Method
corrosion or pitting plus transgranular cracking shall not be
6.1 To rate a new material and test direction, stress-
considered as an SCC failure (Test Method G47).
corrosion tests shall be performed on at least ten random lots.
The highest rating assigned shall be that for which the test
4. Significance and Use
results show 90 % conformance at the 95 % confidence level
4.1 Thisclassificationinvolvesalphabeticalratingsintended
when tested at the following stresses:
only to provide a qualitative guide for materials selection. The
A—Equal to or greater than 75 % of the specified minimum
ratings are based primarily on the results of standard corrosion
yield strength.
tests.
B—Equal to or greater than 50 % of the specified minimum
yield strength.
4.2 Interpretations of the SCC ratings in terms of typical
problem areas including service experience are given in Table C—Equal to or greater than 25 % of the specified minimum
yield strength or 100 MPa (14.5 ksi), whichever is higher.
1. Practical experience has shown that SCC problems with
aluminum alloys generally have involved situations where the D—Fails to meet the criterion for rating C.
direction and magnitude of the tensile stresses resulting from
6.2 Specimens shall be exposed by alternate immersion in
manufacturing or use, or both, of the material were not
3.5 % sodium chloride solution in accordance with Practice
recognized.
G44.
4.3 Al
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