ASTM G64-99
(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
SCOPE
1.1 This standard contains 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.
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Designation: G 64 – 99
Standard Classification of
Resistance to Stress-Corrosion Cracking of Heat-Treatable
Aluminum Alloys
ThisstandardisissuedunderthefixeddesignationG 64;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (e) 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
stresscorrosioncracking(SCC)ofhigh-strengthaluminumalloystoassistintheselectionofmaterials.
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 3. Terminology
1.1 This standard contains alphabetical ratings of the rela- 3.1 Definitions:
tive resistance to SCC of various mill product forms of the 3.1.1 lot—an identifiable quantity of material of the same
wrought 2XXX, 6XXX, and 7XXX series heat-treated alumi- mill form, alloy, temper, section and size (or thickness, in the
num alloys and the procedure for determining the ratings. case of sheet and plate) traceable to a heat treat lot or lots, and
1.2 The ratings do not apply to metal in which the metal- subjected to inspection at one time.
lurgical structure has been altered by welding, forming, or 3.1.2 stress-corrosion cracking (SCC)—a cracking process
other fabrication processes. that requires the simultaneous action of a corrodent and
sustained tensile stress. SCC in aluminum alloy products
2. Referenced Documents
historically has been observed to follow an intergranular path
2.1 ASTM Standards: leading to the ultimate fracture. Thus, for the purpose of this
G 44 Practice for Evaluating Stress Corrosion Cracking
standard, a fractured test specimen that reveals only pitting
ResistanceofMetalsandAlloysbyAlternateImmersionin
corrosion or pitting plus transgranular cracking shall not be
3.5 % Sodium Chloride Solution considered as an SCC failure (Test Method G 47).
G 47 Test Method for Determining Susceptibility to Stress-
4. Significance and Use
Corrosion Cracking of High-Strength Aluminum Alloy
Products 4.1 Thisclassificationinvolvesalphabeticalratingsintended
only to provide a qualitative guide for materials selection. The
ratings are based primarily on the results of standard corrosion
tests.
This classification is under the jurisdiction of ASTM Committee G-1 on
Corrosion of Metals and is the direct responsibility of Subcommittee G01.06 on
4.2 Interpretations of the SCC ratings in terms of typical
Stress Corrosion Cracking and Corrosion Fatigue.
problem areas including service experience are given in Table
Current edition approved Aug. 10, 1999. Published September 1999. Originally
e1 1. Practical experience has shown that SCC problems with
published as G 64 – 80. Last previous edition G 64 –91 (1997) .
Annual Book of ASTM Standards, Vol 03.02. aluminum alloys generally have involved situations where the
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G64
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 treatement, straightening, forming, and so forth.
direction and magnitude of the tensile stresses resulting from A—Equal to or greater than 75 % of the specified minimum
manufacturing or use, or both, of the material were not yield strength.
recognized. B—Equal to or greater than 50 % of the specified minimum
4.3 AlistoftheSCCratingsfortheheat-treatablealuminum yield strength.
alloyproductsisgiveninTable2.Revisionstothetablewillbe C—Equal to or greater than 25 % of the specified minimum
required as new materials become available and additional test yield strength or 100 MPa (14.5 ksi), whichever is higher.
results are accumulated. D—Fails to meet the criterion for rating C.
4.4 These alphabetical ratings are not suitable for direct use 6.2 Specimens shall be exposed by alternate immersion in
in mathematical models for material selection, but numerical 3.5 % sodium chloride solution in accordance with Practice
weights and confidence factors can be devised on thebasis of G 44.
experience and judgment of the materials engineer. 6.3 The length of exposure shall be selected according to
alloy type and specimen orientation as follows:
A
5. Basis of Classification
Test Direction
Alloy Type ST L and LT
5.1 The stress corrosion ratings for new or additional
2XXX 10 days 40 days
materials shall be based on laboratory tests of standard smooth
6XXX 90 days 90 days
7XXX 20 days 40 days
specimens for susceptibility at specified stress levels. The
A
See Footnote B, Table 2.
3.5 % NaCl alternate immersion test (Practice G 44) was
These exposure periods are believed to be long enough to
chosen for the laboratory test because it is widely used for
detect susceptibility to intergranular SCC in each instance, yet
aluminum alloys and is capable of detecting mate
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