ASTM G67 - 24a 确定5XXX系列铝合金在暴露于硝酸后质量损失的晶间腐蚀敏感性的标准试验方法（NAMLT试验

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Designation: G67 −24a
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)
1
This standard is issued under the ﬁxed designation G67; 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
1.1 This test method, also known as the Nitric Acid Mass
Loss Test (NAMLT), covers a procedure for constant immer-
sion intergranular corrosion testing of 5XXX series aluminum
alloys.
1.2 This test method is applicable only to wrought products.
1.3 This test method covers type of specimen, specimen
preparation, test environment, and method of exposure.
1.4 The values stated in SI units are to be regarded as the
standard. The values given in parentheses are for information
only.
1.5 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 appro-
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accor-
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
2
D1193 Speciﬁcation for Reagent Water
E29 Practice for Using Signiﬁcant Digits in Test Data to
Determine Conformance with Speciﬁcations
E691 Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method
G1 Practice for Preparing, Cleaning, and Evaluating Corro-
sion Test Specimens
G16 Guide for Applying Statistics to Analysis of Corrosion
Data
G193 Terminology and Acronyms Relating to Corrosion
3. Terminology
3.1 Deﬁnitions of related terms can be found in Terminol-
ogy G193.
4. Summary of Test Method
4.1 This test method consists of immersing test specimens
in concentrated nitric acid at 30 °C (86 °F) for 24 h and
determining the mass loss per unit area as a measure of
susceptibility to intergranular corrosion.
5. Signiﬁcance and Use
5.1 This test method provides a quantitative measure of the
susceptibility to intergranular corrosion of Al-Mg and Al-
Mg-Mn alloys. The nitric acid dissolves a second phase, an
aluminum-magnesium intermetallic compound (βAl-Mg), in
preference to the solid solution of magnesium in the aluminum
matrix. When this compound is precipitated in a relatively
continuous network along grain boundaries, the effect of the
preferential attack is to corrode around the grains, causing
them to fall away from the specimens. Such dropping out of the
grains causes relatively large mass losses of the order of
25 mg ⁄cm
2
to 75 mg ⁄cm
2
(160 mg ⁄in.
2
to 480 mg ⁄in.
2
),
whereas, samples of intergranular-resistant materials lose only
about 1 mg ⁄cm
2
to 15 mg ⁄cm
2
(10 mg ⁄in.
2
to 100 mg/in.
2
).
When the βAl-Mg compound is randomly distributed, the
preferential attack can result in intermediate mass losses.
Metallographic examination is required in such cases to
establish whether or not the loss in mass is the result of
intergranular attack.
5.2 The precipitation of the second phase in the grain
boundaries also gives rise to intergranular corrosion when the
material is exposed to chloride-containing natural
environments, such as seacoast atmospheres or sea water. The
extent to which the alloy will be susceptible to intergranular
1
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 Association, Inc.
Current edition approved Nov. 1, 2024. Published November 2024. Originally
approved in 1980. Last previous edition approved in 2024 as G67 – 24. DOI:
10.1520/G0067-24A.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at www.astm.org/contact. For Annual Book of
ASTM Standards volume information, refer to the standard’s Document Summary
page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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.
1

corrosion depends upon the degree of precipitate continuity in

the grain boundaries. Visible manifestations of the attack may

be in various forms such as pitting, exfoliation, or stress-

corrosion cracking, depending upon the morphology of the

grain structure and the presence of sustained tensile stress.

6. Interferences

6.1 If all loose particles are not removed during cleaning

after exposure, the mass loss will be low relative to the amount

of corrosion that actually occurred.

7. Apparatus

7.1 Nonmetallic Container—A suitable inert, nonmetallic

container should be used to contain the nitric acid and

specimens during the period of the test. The use of individual

beakers for each specimen is recommended; however, the

immersion of multiple specimens in the same container is

acceptable.

7.1.1 The specimens should be situated in the container so

that none of the major surfaces is in total contact with the walls

of the container. Also, specimens should be isolated electrically

from one another. A recommended method of positioning the

specimens is to incline them so that the edges rest on the

bottom and side wall of the container. See Figs. 1 and 2 for an

example of the recommended conﬁguration, using a 100 mL

non-ﬂuted beaker and a watchglass cover for each specimen

with the beakers immersed in a water bath. This method is

considered to be the optimal conﬁguration for this test

method.

7.1.2 The container should have a loose ﬁtting cover to

reduce evaporation and to conﬁne any fumes evolved by the

acid.

7.2 Laboratory-Grade Water Bath—This test method re-

quires precise temperature control (see 9.2 for tolerances on

test temperature). It is highly recommended that a laboratory-

grade water bath be used. An ideal conﬁguration of specimens

and water bath are shown in Figs. 1 and 2.

7.3 Temperature Measuring Device—Given the extreme

sensitivity to temperature ﬂuctuations, it is recommended that

the temperature be measured continuously with a recording

temperature measurement device.

7.4 Ultrasonic Bath—The corroded specimens will be

cleaned using an ultrasonic cleaning bath (see 12.7). Such

ultrasonic cleaning baths are available from all of the common

laboratory supply companies and typically have an operating

frequency of 40 kHz and 15 W ⁄L to 50 W ⁄L ultrasonic power.

8. Reagents

8.1 Purity of Reagents—The nitric acid (HNO

) test solu-

tion shall be reagent grade within the range of 69 w ⁄w % to

70 w ⁄w %. The sodium hydroxide (NaOH) solution used for

etching and the HNO

(67 w ⁄w % to 70 w ⁄w %) used for

desmutting shall also be reagent grade.

8.2 Purity of Water—Use water conforming to Speciﬁcation

D1193 Type IV to prepare the NaOH solution and for rinsing

and ultrasonic cleaning purposes.

9. Test Solution

9.1 Use sufficient test solution to fully immerse the speci-

mens and constitute a volume to specimen surface area ratio of

at least 30 L/m

(19 mL/in.

9.2 Maintain the test solution temperature at 30 °C 60.1 °C

(86 °F 60.2 °F).

10. Sampling

10.1 The speciﬁc location of samples in a mill product, the

number of samples that should be tested, and so forth, are

outside the scope of this standard.

Craig, H. L. Jr., “Nitric Acid Weight Loss Test for the H116 and H117 Tempers

of 5086 and 5456 Aluminum Alloys,” Localized Corrosion—Cause of Metal

Failure, ASTM STP 516, ASTM, 1972, pp. 17–37.

Aluminum Association Technical Report T1, “Exfoliation Corrosion Testing of

Aluminum Alloys 5086 and 5456,” T.J. Summerson, D.O. Sprowls. Published circa

1975. Currently out-of-print. Hard copies can be acquired from the Aluminum

Association.

FIG. 1 Recommended Conﬁguration for Specimen Exposure; A 100 mL Non-ﬂuted Beaker and Watchglass

G67 − 24a

11. Test Specimens

11.1 Prepare specimens with dimensions 50 mm by 6 mm

(2 in. by 0.25 in.) by product thickness. The 50 mm dimension

shall be parallel to the longitudinal direction of the product.

11.2 If the thickness of the product is greater than 25 mm

(1 in.), reduce it by one half or to 25 mm, whichever is less,

while retaining one original as-fabricated surface. All sawn

surfaces shall be machined to the ﬁnal dimensions.

11.3 A small drilled hole (<4 mm diameter) is permitted to

facilitate cleaning (see Fig. 3). The additional surface area of

the hole-wall is insigniﬁcant and it is therefore not necessary to

include the surface area of the hole in the total sample area.

11.4 Take a minimum of two specimens from each sample.

12. Procedure

12.1 Smooth all edges with a ﬁne ﬁle or ﬁne emery paper

(320).

12.2 Identiﬁcation of specimens can be achieved by either

scribing or stamping. Conﬁne identiﬁcation of specimens to an

as-fabricated surface.

12.3 Measure all three dimensions to the nearest 0.02 mm

(0.001 in.), and calculate the total surface area.

12.4 Immerse the specimens in 5 % NaOH solution at 80 °C

(176 °F) for 1 min followed by a water rinse, a 30 s immersion

in concentrated HNO

(desmut), and a water rinse. Allow the

specimens to air dry. Do not wipe dry with a cloth or paper

towel.

12.5 Weigh the specimens to the nearest 1.0 mg.

12.6 Immerse the specimens in the test solution for 24 h.

12.7 Remove the specimens and rinse them in water to

remove the acid. Immerse the specimens in puriﬁed water (see

8.2) in an ultrasonic bath. Cleaning of multiple specimens can

be facilitated by stringing the specimens on a coated wire with

spacers between the specimens and suspending in the ultra-

sonic bath as illustrated in Fig. 3. Ultrasonically clean them for

between 1 min and 2 min, followed by a DI water rinse and

air-dry, or blow dry with compressed air.

NOTE 1—If using compressed air, care should be taken to ensure it is

free of dirt, oils, etc.

12.8 Weigh the specimens and determine mass losses to the

nearest 0.1 mg. Re-clean (in accordance with 12.7) to obtain a

constant weight in accordance with Practice G1.

12.9 Calculate the mass losses per unit area and express as

mg/cm

to the nearest whole number using rounding rules of

Practice E29.

NOTE 2—Optional—To ascertain the morphology of corrosion, the

specimen can be cross-sectioned, polished, and examined metallographi-

cally after the mass loss determination.

FIG. 2 100 mL Beakers Inserted into a Water-bath, Using an Aluminum Template

G67 − 24a

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标签： #腐蚀 #铝合金 #合金

摘要：

本页面详细介绍了ASTM G67 - 24a标准试验方法，专门用于测定5XXX系列铝合金在暴露于硝酸后的质量损失，以评估其晶间腐蚀敏感性（即NAMLT试验）。该标准通过精确的硝酸浸泡与称重流程，帮助检测材料在腐蚀环境下的性能退化，适用于航空、船舶及汽车工业中广泛使用的5XXX系铝合金。文档涵盖试验原理、试样制备、试剂要求、结果计算及质量控制要点，是工程师与质检人员判断铝合金抗晶间腐蚀能力的权威参考。

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ASTM G67 - 24a 确定5XXX系列铝合金在暴露于硝酸后质量损失的晶间腐蚀敏感性的标准试验方法（NAMLT试验

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