ASTM G66-23

Standard Test Method for Visual Assessment of Exfoliation Corrosion Susceptibility of 5XXX Series Aluminum Alloys (ASSET Test)

SIGNIFICANCE AND USE
5.1 This test method provides a reliable prediction of the exfoliation corrosion behavior of Al-Mg alloys in marine environments.4,5,6 The test is useful for alloy development studies and quality control of mill products such as sheet and plate.
SCOPE
1.1 This test method covers a procedure for continuous immersion exfoliation corrosion testing of 5XXX series aluminum-magnesium alloys containing 2.0 % or more magnesium.  
1.2 This test method applies only to wrought products.  
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, 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

• Status: Published
• Publication Date: 30-Nov-2023
• ICS: 77.040.30 - Chemical analysis of metals
• Technical Committee: G01 - Corrosion of Metals
• Drafting Committee: G01.05 - Laboratory Corrosion Tests

Relations

• Replaces: ASTM G66-99(2018)e1 - Standard Test Method for Visual Assessment of Exfoliation Corrosion Susceptibility of 5XXX Series Aluminum Alloys (ASSET Test)
• Effective Date: 01-Dec-2023
• Referred By: ASTM G112-22 - Standard Guide for Conducting Exfoliation Corrosion Tests in Aluminum Alloys
• Effective Date: 01-Dec-2023
• Referred By: ASTM B928/B928M-15(2023)e1 - Standard Specification for High Magnesium Aluminum-Alloy Products for Marine Service and Similar Environments
• Effective Date: 01-Dec-2023
• Referred By: ASTM G31-21 - Standard Guide for Laboratory Immersion Corrosion Testing of Metals
• Effective Date: 01-Dec-2023

Overview

ASTM G66-23: Standard Test Method for Visual Assessment of Exfoliation Corrosion Susceptibility of 5XXX Series Aluminum Alloys (ASSET Test) is a key international standard developed by ASTM International. This test method provides a consistent procedure for assessing the susceptibility of 5XXX series aluminum-magnesium (Al-Mg) alloys-containing at least 2.0% magnesium-to exfoliation corrosion. The method is specifically designed for continuous immersion testing of wrought aluminum products, such as sheet and plate, providing critical data for both alloy development and quality control in industries where corrosion resistance in marine or aggressive environments is vital.

Key Topics

• Exfoliation Corrosion: Defined as subsurface corrosion progressing laterally from the initiation sites along planes parallel to the surface-predominantly at grain boundaries-exfoliation corrosion results in the formation of corrosion products that force the metal away from the base material, creating a layered, book-page-like appearance.
• Visual Assessment: After exposure, test specimens are visually examined and rated using standard reference photographs and a prescribed grading system, offering an objective assessment of corrosion susceptibility.
• Test Procedure Highlights:
  • Specimens are immersed in a specified test solution at controlled temperature (65 ± 1°C) for 24 hours.
  • Fresh solution and precise specimen preparation are required for every test run to ensure reliability.
  • The degree of corrosion is categorized with codes (N: No attack, P: Pitting, E: Exfoliation) and sub-graded to reflect severity.
• Quality and Reproducibility: Control specimens with known susceptibility are included to validate test conditions. Interlaboratory studies have shown the method to be repeatable and reproducible across different facilities and operators.

Applications

ASTM G66-23 is widely applied in the following areas:

• Alloy Development: Essential for research and development teams, this method offers a predictive tool for evaluating the corrosion performance of new and existing Al-Mg alloy formulations in aggressive environments, helping guide material design.
• Quality Control: The method supports manufacturers in consistently verifying the corrosion resistance of aluminum sheet and plate products, minimizing the risk of field failures.
• Marine and Industrial Sectors: Particularly valuable for aluminum used in marine vessels, offshore structures, transportation, and chemical processing equipment where 5XXX series alloys are favored for their strength-to-weight ratio and corrosion resistance.
• Specification Compliance: Helps suppliers and buyers enforce compliance with corrosion resistance specifications relevant to end-use requirements.

Related Standards

For comprehensive corrosion assessment and terminology, ASTM G66-23 references or complements the following standards:

• ASTM D1193: Specification for Reagent Water, ensuring purity for test solutions.
• ASTM G15: Terminology and Acronyms Relating to Corrosion and Corrosion Testing.
• ASTM G67: Test Method for Determining the Susceptibility to Intergranular Corrosion of 5XXX Series Aluminum Alloys by Mass Loss After Nitric Acid Immersion.
• Industry Standards: May be used alongside aluminum product specifications and other corrosion test methods for a complete evaluation of material performance.
• International Alignment: Developed under WTO Technical Barriers to Trade (TBT) Committee principles, ensuring global recognition and applicability.

By following ASTM G66-23, organizations can reliably assess the visual exfoliation corrosion susceptibility of 5XXX series aluminum alloys, supporting improved material durability and performance in demanding applications. This standard remains a crucial resource for maintaining product quality, advancing material science, and ensuring engineering reliability where corrosion resistance is non-negotiable.

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: G66 − 23
Standard Test Method for
Visual Assessment of Exfoliation Corrosion Susceptibility of
5XXX Series Aluminum Alloys (ASSET Test)
This standard is issued under the fixed designation G66; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
3.1 Definitions:
1.1 This test method covers a procedure for continuous
immersion exfoliation corrosion testing of 5XXX series 3.1.1 exfoliation corrosion, n—subsurface corrosion that
proceeds laterally from the sites of initiation along planes
aluminum-magnesium alloys containing 2.0 % or more mag-
nesium. parallel to the surface forming corrosion products that force
metal away from the body of the material, giving rise to a
1.2 This test method applies only to wrought products.
layered appearance resembling the pages of a book. (see
1.3 The values stated in SI units are to be regarded as the
Terminology G193).
standard. The values given in parentheses are for information
only.
4. Summary of Test Method
1.4 This standard does not purport to address all of the
4.1 Specimens are immersed for 24 h at 65 °C 6 1 °C
safety concerns, if any, associated with its use. It is the
(150 °F 6 2 °F) in a solution containing ammonium chloride,
responsibility of the user of this standard to establish appro-
ammonium nitrate, ammonium tartrate, and hydrogen perox-
priate safety, health, and environmental practices and deter-
ide. The susceptibility to exfoliation is determined by visual
mine the applicability of regulatory limitations prior to use.
examination using performance ratings established by refer-
1.5 This international standard was developed in accor-
ence to standard photographs.
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
5. Significance and Use
Development of International Standards, Guides and Recom-
5.1 This test method provides a reliable prediction of the
mendations issued by the World Trade Organization Technical
exfoliation corrosion behavior of Al-Mg alloys in marine
Barriers to Trade (TBT) Committee.
4,5,6
environments. The test is useful for alloy development
studies and quality control of mill products such as sheet and
2. Referenced Documents
plate.
2.1 ASTM Standards:
D1193 Specification for Reagent Water
6. Apparatus
G193 Terminology and Acronyms Relating to Corrosion
6.1 Any suitable glass or plastic container can be used to
2.2 ASTM Adjunct:
contain the solution and specimens during the test period.
ASSET Tested Specimens (2 figs, Fig. 1, 2; 8.5 × 11 in.)
Depending upon the shape and size of the specimens, rods or
PDF Download
racks of glass, plastic, or other inert substance shall be used to
support the specimens above the bottom of the container. The
container should be fitted with a removable cover to reduce
evaporation.
This test method is under the jurisdiction of ASTM Committee G01 on
Corrosion of Metals and is the direct responsibility of Subcommittee G01.05 on
Laboratory Corrosion Tests. This method was developed by a joint task group with
The Aluminum Assoc., Inc.
Current edition approved Dec. 1, 2023. Published December 2023. Originally Aluminum Association Technical Report T1, “Exfoliation Corrosion Testing of
ɛ1
approved in 1980. Last previous edition approved in 2018 as G66 – 99 (2018) . Aluminum Alloys 5086 and 5456”.
DOI: 10.1520/G0066-23. Sprowls, D. O., Walsh, J. D. and Shumaker, M. B., “Simplified Exfoliation
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Testing of Aluminum Alloys”, Localized Corrosion—Cause of Metal Failure, ASTM
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM STP 516, ASTM, 1972, pp 38–65.
Standards volume information, refer to the standard’s Document Summary page on Summerson T. J., Interim Report, Aluminum Association Task Group on
the ASTM website. Exfoliation and Stress Corrosion Cracking of Aluminum Alloys for Boat Stock;
Available from ASTM International Headquarters. Order Adjunct No. Proceedings Tri-Service Corrosion Military Equipment Conference, October 29–31,
ADJG0066-E-PDF. Original adjunct produced in 1987. 1974; Technical Report AFML-TR-75-42, Vol. II, p. 193–221, February 1, 1975.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G66 − 23
7. Reagents 11.2 The control may be any material of the Al-Mg series
that has a well-documented susceptibility to exfoliation
7.1 Purity of Reagents—Reagent grade chemicals shall be
corrosion, preferably one with an intermediate susceptibility.
used in all tests.
7.2 Purity of Water—Distilled or deionized water conform-
12. Procedure
ing to Specification D1193. Type IV shall be used to prepare
12.1 Degrease the specimens with a suitable solvent. After
the test solution except chloride ion sodium limits can be
degreasing, prepare specimens as follows: Etch 1 min in 5 %
disregarded.
by weight sodium hydroxide solution at 80 °C (176 °F), rinse
in water, desmut 30 s in concentrated nitric acid at room
8. Test Solution
temperature, rinse with distilled or deionized water, air dry.
8.1 Preparation of Test Solution:
8.1.1 The test solution shall have the following composi- NOTE 2—If specimens are not to be immersed in the test solution
immediately, they should be stored in a desiccator maintained at less than
tion:
1 % relative humidity (use fresh desiccant such as activated alumina or
NH Cl (1.0 M)
anhydrous calcium sulfate).
NH NO (0.25 M)
4 3
(NH ) C H O (0.01 M) 12.2 Use fresh solution at the start of each test.
4 2 4 4 6
H O (0.09 M)
2 2
12.3 Immerse the specimens vertically with the top edge of
8.1.2 In separate containers, dissolve 53.5 g ammonium
the specimens at least 25 mm (1 in.) below the surface of the
chloride (NH Cl), 20.0 g ammonium nitrate (NH NO ), 1.8 g
4 4 3
solution and the bottom edge at least 25 mm above the bottom
ammonium tartrate ((NH ) C H O ), and 10 mL of 30 % stock
4 2 4 4 6
of the container.
solution hydrogen peroxide (H O ) in a small amount of water.
2 2
12.4 Immerse the specimens in the test solution continu-
After dissolving, mix the components together thoroughly and
ously for 24 h.
adjust the final dilution to 1 L.
12.5 Rinse the specimens gently in running tap water
NOTE 1—If a stock solution of the above chemicals is to be stored, the
immediately after removal from the solution, then soak in
hydrogen peroxide should not be added until the solution is heated for the
test.
concentrated nitric acid at room temperature until they appear
clean, again rinse in water, and air dry.
8.2 The solution will have a typical pH of 5.2 to 5.4.
12.5.1 Air-blast drying is to be avoided in order to prevent
8.3 The solution shall be used in sufficient quantity to
mechanical removal of exfoliated metal.
provide a volume-to-exposed specimen surface area ratio of at
2 2
least 100
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1
Designation: G66 − 99 (Reapproved 2018) G66 − 23
Standard Test Method for
Visual Assessment of Exfoliation Corrosion Susceptibility of
5XXX Series Aluminum Alloys (ASSET Test)
This standard is issued under the fixed designation G66; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Adjunct description in 2.2 and adjunct stock number in Footnote 4 were updated editorially in February 2023.
1. Scope
1.1 This test method covers a procedure for continuous immersion exfoliation corrosion testing of 5XXX series aluminum-
magnesium alloys containing 2.0 % or more magnesium.
1.2 This test method applies only to wrought products.
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, 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.
2. Referenced Documents
2.1 ASTM Standards:
D1193 Specification for Reagent Water
G15G193 Terminology and Acronyms Relating to Corrosion and Corrosion Testing (Withdrawn 2010)
2.2 ASTM Adjunct:
ASSET Tested Specimens (2 figs, Fig. 1, 2; 8.5 × 11 in.) PDF Download
3. Terminology
3.1 Definitions:
3.1.1 exfoliation—exfoliation corrosion, n—subsurface corrosion that proceeds laterally from the sites of initiation along planes
parallel to the surface, generally at grain boundaries, surface forming corrosion products that force metal away from the body of
the material, giving rise to a layered appearance resembling the pages of a book. (see Terminology G15G193).
This test method is under the jurisdiction of ASTM Committee G01 on Corrosion of Metals and is the direct responsibility of Subcommittee G01.05 on Laboratory
Corrosion Tests. This method was developed by a joint task group with The Aluminum Assoc., Inc.
Current edition approved Oct. 1, 2018Dec. 1, 2023. Published November 2018December 2023. Originally approved in 1980. Last previous edition approved in 20132018
ɛ1
as G66 – 99 (2013).(2018) . DOI: 10.1520/G0066-99R18E01.10.1520/G0066-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from ASTM International Headquarters. Order Adjunct No. ADJG0066-E-PDF. Original adjunct produced in 1987.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G66 − 23
4. Summary of Test Method
4.1 Specimens are immersed for 24 h at 65 6 1°C (150 6 2°F)24 h at 65 °C 6 1 °C (150 °F 6 2 °F) in a solution containing
ammonium chloride, ammonium nitrate, ammonium tartrate, and hydrogen peroxide. The susceptibility to exfoliation is
determined by visual examination using performance ratings established by reference to standard photographs.
5. Significance and Use
5.1 This test method provides a reliable prediction of the exfoliation corrosion behavior of Al-Mg alloys in marine
4,5,6
environments. The test is useful for alloy development studies and quality control of mill products such as sheet and plate.
6. Apparatus
6.1 Any suitable glass or plastic container can be used to contain the solution and specimens during the test period. Depending
upon the shape and size of the specimens, rods or racks of glass, plastic, or other inert substance shall be used to support the
specimens above the bottom of the container. The container should be fitted with a removable cover to reduce evaporation.
7. Reagents
7.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests.
7.2 Purity of Water—Distilled or deionized water conforming to Specification D1193. Type IV shall be used to prepare the test
solution except chloride ion sodium limits can be disregarded.
8. Test Solution
8.1 Preparation of Test Solution:
8.1.1 The test solution shall have the following composition:
NH Cl (1.0 M)
NH NO (0.25 M)
4 3
(NH ) C H O (0.01 M)
4 2 4 4 6
H O (0.09 M)
2 2
8.1.2 Dissolve In separate containers, dissolve 53.5 g ammonium chloride (NH Cl), 20.0 g ammonium nitrate (NH NO ), 1.8 g
4 4 3
ammonium tartrate ((NH ) C H O ), and 10 mL of 30 % stock solution hydrogen peroxide (H O ) in a small amount of water.
4 2 4 4 6 2 2
After dissolving, mix the components together thoroughly and adjust the final dilution to 1 L.
NOTE 1—If a stock solution of the above chemicals is to be stored, the hydrogen peroxide should not be added until the solution is heated for the test.
8.2 The solution will have a typical pH of 5.2 to 5.4.
8.3 The solution shall be used in sufficient quantity to provide a volume-to-exposed specimen surface area ratio of at least 100
2 2
L/m (65 mL/in. ).
8.4 The temperature of the solution shall be maintained at 65 6 1°C (150 6 2°F).65 °C 6 1 °C (150 °F 6 2 °F).
9. Sampling
9.1 The procedure for sampling mill products is covered in product specifications, or otherwise, and is considered outside the
scope of this standard.
Aluminum Association Technical Report T1, “Exfoliation Corrosion Testing of Aluminum Alloys 5086 and 5456”.
Sprowls, D. O., Walsh, J. D. and Shumaker, M. B., “Simplified Exfoliation Testing of Aluminum Alloys”, Localized Corrosion—Cause of Metal Failure,ASTM STP 516,
ASTM, 1972, pp 38–65.
Summerson T. J., Interim Report, Aluminum Association Task Group on Exfoliation and Stress Corrosion Cracking of Aluminum Alloys for Boat Stock; Proceedings
Tri-Service Corrosion Military Equipment Conference, October 29–31, 1974; Technical Report AFML-TR-75-42, Vol. II, p. 193–221, February 1, 1975.
G66 − 23
10. Test Specimen
10.1 While this test method can be used with any form of specimen or part that can be immersed in the test solution, it is preferred
that specimens be at least 4040 mm by 100 mm (1.5 by 4.0 in.) (1.5 in. by 4.0 in.) with the metal working direction in the 40-mm
(1.5-in.)40 mm (1.5 in.) dimension.
10.2 The specimens should be sawed or machined to minimize introducing residual stresses in edges during preparation of the
specimens (sheared edges are allowed only if the edges are sufficiently dressed or filed down a distance equal to the thickness of
the specimen in order to remove metal deformed by shearing).
11. Standardization
11.1 To provide an indication when some inadvertent deviation from the correct test conditions occurs, it is necessary to expose
to the test at regular intervals a control specimen of a material of known susceptibility. This control should exhibit the same degree
of exfoliati
...