ASTM G67-99

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: G 67 – 99
Standard Test Method for
Determining the Susceptibility to Intergranular Corrosion of
5XXX Series Aluminum Alloys by Mass Loss After Exposure
to Nitric Acid (NAMLT Test)
This standard is issued under the fixed designation G 67; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope continuous network along grain boundaries, the effect of the
preferential attack is to corrode around the grains, causing
1.1 This test method describes a procedure for constant
them to fall away from the specimens. Such dropping out of the
immersion intergranular corrosion testing of 5XXX series
grains causes relatively large mass losses of the order of 25 to
aluminum alloys.
2 2
75 mg/cm (160 to 480 mg/in ), whereas, samples of
1.2 This test method is applicable only to wrought products.
intergranular-resistant materials lose only about 1 to 15 mg/
1.3 This test method covers type of specimen, specimen
2 2
cm (10 to 100 mg/in ). When the bAl-Mg compound is
preparation, test environment, and method of exposure.
randomly distributed, the preferential attack can result in
1.4 The values stated in SI units are to be regarded as the
intermediate mass losses. Metallographic examination is re-
standard.
quired in such cases to establish whether or not the loss in mass
1.5 This standard does not purport to address all of the
is the result of intergranular attack.
safety concerns, if any, associated with its use. It is the
4.2 The precipitation of the second phase in the grain
responsibility of the user of this standard to establish appro-
boundaries also gives rise to intergranular corrosion when the
priate safety and health practices and determine the applica-
material is exposed to chloride-containing natural environ-
bility of regulatory limitations prior to use.
ments, such as seacoast atmospheres or sea water. The extent to
2. Referenced Documents which the alloy will be susceptible to intergranular corrosion
depends upon the degree of precipitate continuity in the grain
2.1 ASTM Standards:
boundaries. Visible manifestations of the attack may be in
D 1193 Specification for Reagent Water
various forms such as pitting, exfoliation, or stress-corrosion
G 1 Practice for Preparing, Cleaning, and Evaluating Cor-
cracking, depending upon the morphology of the grain struc-
rosion Test Specimens
ture and the presence of sustained tensile stress.
3. Summary of Test Method
5. Interferences
3.1 This test method consists of immersing test specimens
5.1 If all loose particles are not removed during cleaning
in concentrated nitric acid at 30°C (86°F) for 24 h and
after exposure, the mass loss will be low relative to the amount
determining the mass loss per unit area as a measure of
of corrosion that actually occurred.
susceptibility to intergranular corrosion.
6. Apparatus
4. Significance and Use
6.1 Nonmetallic Container—A suitable inert, nonmetallic
4.1 This test method provides a quantitative measure of the
container should be used to contain the nitric acid and
susceptibility to intergranular corrosion of Al-Mg and Al-
specimens during the period of the test. The use of individual
Mg-Mn alloys. The nitric acid dissolves a second phase, an
beakers for each specimen is recommended; however, the
aluminum-magnesium intermetallic compound (bAl-Mg), in
immersion of multiple specimens in the same container is
preference to the solid solution of magnesium in the aluminum
acceptable.
matrix. When this compound is precipitated in a relatively
6.1.1 The specimens should be situated in the container so
that none of the major surfaces is in total contact with the walls
This test method is under the jurisdiction of ASTM Committee G-1 on
of the container. Also, specimens should be isolated electrically
Corrosion of Metals and is the direct responsibility of Subcommittee G01.05 on
from one another. A recommended method of positioning the
Laboratory Corrosion Tests. This method was developed by a joint task group with
The Aluminum Association, Inc.
Current edition approved Aug. 10, 1999. Published October 1999. Originally
published as G 67 – 80. Last previous edition G 67 – 93. Craig, H. L. Jr., “Nitric Acid Weight Loss Test for the H116 and H117 Tempers
Annual Book of ASTM Standards, Vol 11.01. of 5086 and 5456 Aluminum Alloys,” Localized Corrosion—Cause of Metal
Annual Book of ASTM Standards, Vol 03.02. Failure, ASTM STP 516, ASTM, pp. 17–37, 1972.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
G67
specimens is to incline them so that the edges rest on the 11.7 Remove the specimens, and rinse with water while
bottom and side wall of the container. brushing with a stiff plastic bristle brush, for example, a
6.1.2 The container should have a loose fitting cover to toothbrush, to remove all adhering particles. Allow to air dry.
reduce evaporation and to confine any fumes evolved by the 11.8 Weigh the specimens and determine mass losses to no
acid. more than 6 1.0 mg, preferably 0.1 mg. Reclean to obtain a
constant weight in accordance with Practice G 1.
7. Reagents 11.9 Calculate the mass losses per unit area and express as
mg/cm to the nearest whole number.
7.1 Purity of Reagents—The nitri
...