ASTM G64-99(2021)
(Classification)Standard Classification of Resistance to Stress-Corrosion Cracking of Heat-Treatable Aluminum Alloys
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. (A) The sum of all stresses including those from service loads (applied), heat treatment, straightening, forming, and so forth.
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. (A) The ratings apply to standard mill products in the types of tempers indicated, including stress-relieved tempers, and could be invalidated in some cases by application of nonstandard thermal treatments or mechanical deformation at room temperature by the user.(B) Test direction refers to orientation of the stressing direction relative to the directional grain structure typical of wrought materials, which in the case of extrusions and forgings may not be predictable from the geometrical cross section of the product.
L — Longitudinal: parallel to direction of principal metal extension during manufacture of the product.
LT—Long Transverse: perpendicular to direction of principal metal extension. In products whose grain structure clearly shows directionality (width-to-thickness ratio greater than two) it is that perpendicular direction parallel to the major grain dimension.
ST—Short Transverse: perpendicular to direction of principal metal extension and parallel to minor dimension of grains in products with significant grain directionality.(C) Sections wit...
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 standard. The values given in parentheses after SI units are provided for information only and are not considered standard.
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
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Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: G64 −99 (Reapproved 2021)
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
Stress-corrosion behavior is an important characteristic to be considered when optimizing the
choice 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 1.5 This international standard was developed in accor-
dance with internationally recognized principles on standard-
1.1 This classification covers alphabetical ratings of the
ization established in the Decision on Principles for the
relative resistance to SCC of various mill product forms of the
Development of International Standards, Guides and Recom-
wrought 2XXX, 6XXX, and 7XXX series heat-treated alumi-
mendations issued by the World Trade Organization Technical
num alloys and the procedure for determining the ratings.
Barriers to Trade (TBT) Committee.
1.2 The ratings do not apply to metal in which the metal-
2. Referenced Documents
lurgical structure has been altered by welding, forming, or
other fabrication processes.
2.1 ASTM Standards:
G44 PracticeforExposureofMetalsandAlloysbyAlternate
1.3 The values stated in SI units are to be regarded as
Immersion in Neutral 3.5 % Sodium Chloride Solution
standard. The values given in parentheses after SI units are
G47 Test Method for Determining Susceptibility to Stress-
provided for information only and are not considered standard.
Corrosion Cracking of 2XXX and 7XXX Aluminum
1.4 This standard does not purport to address all of the
Alloy Products
safety concerns, if any, associated with its use. It is the
2.2 Other Documents:
responsibility of the user of this standard to establish appro-
MIL-HANDBOOK-5 Metallic Materials and Elements for
priate safety, health, and environmental practices and deter- 3
Aerospace Vehicle Structures
mine the applicability of regulatory limitations prior to use.
MIL-STD-1568 Materials and Processes for Corrosion Pre-
vention and Control in Aerospace Systems
1 2
This classification is under the jurisdiction of ASTM Committee G01 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Corrosion of Metals and is the direct responsibility of Subcommittee G01.06 on contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Environmentally Assisted Cracking. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Aug. 1, 2021. Published August 2021. Originally the ASTM website.
approved in 1980. Last previous edition approved in 2013 as G64 – 99 (2013). DOI: Available from DLA Document Services, Building 4/D, 700 Robbins Ave.,
10.1520/G0064-99R21. Philadelphia, PA 19111-5094, http://quicksearch.dla.mil.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G64 − 99 (2021)
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.
MSFC-SPEC-522A Design Criteria for Controlling Stress weights and confidence factors can be devised on the basis of
4 5
Corrosion Cracking experience and judgment of the materials engineer.
5. Basis of Classification
3. Terminology
5.1 The stress-corrosion ratings for new or additional ma-
3.1 Definitions:
terials shall be based on laboratory tests of standard smooth
3.1.1 lot—an identifiable quantity of material of the same
specimens for susceptibility at specified stress levels. The
mill form, alloy, temper, section, and size (or thickness, in the
3.5 % NaCl alternate immersion test (Practice G44) was
case of sheet and plate) traceable to a heat treat lot or lots, and
chosen for the laboratory test because it is widely used for
subjected to inspection at one time.
aluminum alloys and is capable of detecting materials that
3.1.2 stress-corrosion cracking (SCC)—a cracking process
would be likely to be susceptible to SCC in natural environ-
that requires the simultaneous action of a corrodent and
ments.
sustained tensile stress. SCC in aluminum alloy products
5.2 Other types of tests using precracked specimens or
historically has been observed to follow an intergranular path
dynamic loading have promise as alternative or supplemen-
leading to the ultimate fracture. Thus, for the purpose of this
tary methods, but they presently require better understanding
standard, a fractured test specimen that reveals only pitting
and standardization.
corrosion or pitting plus transgranular cracking shall not be
considered as an SCC failure (Test Method G47).
6. Test Method
4. Significance and Use 6.1 To rate a new material and test direction, stress-
corrosion tests shall be performed on at least ten random lots.
4.1 Thisclassificationinvolvesalphabeticalratingsintended
The highest rating assigned shall be that for which the test
only to provide a qualitative guide for materials selection. The
results show 90 % conformance at the 95 % confidence level
ratings are based primarily on the results of standard corrosion
when tested at the following stresses:
tests.
A—Equal to or greater than 75 % of the specified minimum
4.2 Interpretations of the SCC ratings in terms of typical
yield strength.
problem areas including service experience are given in Table
B—Equal to or greater than 50 % of the specified minimum
1. P
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