1、Designation: G67 13Standard Test Method forDetermining the Susceptibility to Intergranular Corrosion of5XXX Series Aluminum Alloys by Mass Loss After Exposureto Nitric Acid (NAMLT Test)1This standard is issued under the fixed designation G67; the number immediately following the designation indicate
2、s the year of originaladoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscriptepsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method describes a procedure for con
3、stantimmersion intergranular corrosion testing of 5XXX seriesaluminum alloys.1.2 This test method is applicable only to wrought products.1.3 This test method covers type of specimen, specimenpreparation, test environment, and method of exposure.1.4 The values stated in SI units are to be regarded as
4、 thestandard. The values given in parentheses are for informationonly.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the
5、 applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterG1 Practice for Preparing, Cleaning, and Evaluating Corro-sion Test Specimens3. Summary of Test Method3.1 This test method consists of immersing test specimensin con
6、centrated nitric acid at 30C (86F) for 24 h anddetermining the mass loss per unit area as a measure ofsusceptibility to intergranular corrosion.4. Significance and Use4.1 This test method provides a quantitative measure of thesusceptibility to intergranular corrosion of Al-Mg and Al-Mg-Mn alloys. Th
7、e nitric acid dissolves a second phase, analuminum-magnesium intermetallic compound (Al-Mg), inpreference to the solid solution of magnesium in the aluminummatrix. When this compound is precipitated in a relativelycontinuous network along grain boundaries, the effect of thepreferential attack is to
8、corrode around the grains, causingthem to fall away from the specimens. Such dropping out of thegrains causes relatively large mass losses of the order of 25 to75 mg/cm2(160 to 480 mg/in2), whereas, samples ofintergranular-resistant materials lose only about 1 to 15 mg/cm2(10 to 100 mg/in2). When th
9、e Al-Mg compound israndomly distributed, the preferential attack can result inintermediate mass losses. Metallographic examination is re-quired in such cases to establish whether or not the loss in massis the result of intergranular attack.4.2 The precipitation of the second phase in the grainbounda
10、ries also gives rise to intergranular corrosion when thematerial is exposed to chloride-containing naturalenvironments, such as seacoast atmospheres or sea water. Theextent to which the alloy will be susceptible to intergranularcorrosion depends upon the degree of precipitate continuity inthe grain
11、boundaries. Visible manifestations of the attack maybe in various forms such as pitting, exfoliation, or stress-corrosion cracking, depending upon the morphology of thegrain structure and the presence of sustained tensile stress.35. Interferences5.1 If all loose particles are not removed during clea
12、ningafter exposure, the mass loss will be low relative to the amountof corrosion that actually occurred.6. Apparatus6.1 Nonmetallic ContainerA suitable inert, nonmetalliccontainer should be used to contain the nitric acid and1This test method is under the jurisdiction of ASTM Committee G01 onCorrosi
13、on of Metals and is the direct responsibility of Subcommittee G01.05 onLaboratory Corrosion Tests. This method was developed by a joint task group withThe Aluminum Association, Inc.Current edition approved May 1, 2013. Published May 2013. Originallyapproved in 1980. Last previous edition approved in
14、 2004 as G67 04, which waswithdrawn January 2013 and reinstated May 2013. DOI: 10.1520/G0067-13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Docume
15、nt Summary page onthe ASTM website.3Craig, H. L. Jr., “Nitric Acid Weight Loss Test for the H116 and H117 Tempersof 5086 and 5456 Aluminum Alloys,” Localized CorrosionCause of MetalFailure, ASTM STP 516, ASTM, 1972, pp. 1737.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Cons
16、hohocken, PA 19428-2959. United States1specimens during the period of the test. The use of individualbeakers for each specimen is recommended; however, theimmersion of multiple specimens in the same container isacceptable.6.1.1 The specimens should be situated in the container sothat none of the maj
17、or surfaces is in total contact with the wallsof the container.Also, specimens should be isolated electricallyfrom one another. A recommended method of positioning thespecimens is to incline them so that the edges rest on thebottom and side wall of the container.6.1.2 The container should have a loo
18、se fitting cover toreduce evaporation and to confine any fumes evolved by theacid.7. Reagents7.1 Purity of ReagentsThe nitric acid (HNO3) test solu-tion shall be reagent grade and have a specific gravity withinthe range of 1.4134 to 1.4218 (70 to 72 weight %). The sodiumhydroxide (NaOH) solution use
19、d for etching and the HNO3(70to 72 weight %) used for desmutting shall also be reagentgrade.7.2 Purity of WaterUse water conforming to SpecificationD1193 Type IV to prepare the NaOH solution and for rinsingpurposes.8. Test Solution8.1 Use sufficient test solution to fully immerse the speci-mens and
20、constitute a volume to specimen surface area ratio ofat least 30 L/m2(19 mL/in2).8.2 Maintain the test solution temperature at 30 6 0.1C (866 0.2F).9. Sampling9.1 The specific location of samples in a mill product, thenumber of samples that should be tested, and so forth, areoutside the scope of thi
21、s standard.10. Test Specimens10.1 Prepare specimens with dimensions 50 mm by 6 mm (2in. by 0.25 in.) by product thickness. The 50-mm dimensionshall be parallel to the longitudinal direction of the product.10.2 If the thickness of the product is greater than 25 mm (1in.), reduce it by one half or to
22、25 mm, whichever is less, whileretaining one original as-fabricated surface. All sawn surfacesshall be machined to the final dimensions.10.3 Take a minimum of two specimens from each sample.11. Procedure11.1 Smooth all edges with a fine file or fine emery paper(320).11.2 Identification of specimens
23、can be achieved by eitherscribing or stamping. Confine identification of specimens to anas-fabricated surface.11.3 Measure all three dimensions to the nearest 0.02 mm(0.001 in.), and calculate the total surface area.11.4 Immerse the specimens in 5 % NaOH solution at 80C(176F) for 1 min followed by a
24、 water rinse, a 30-s immersionin HNO3(desmut), and a water rinse. Allow the specimens toair dry. Do not wipe dry with a cloth or paper towel.11.5 Weigh the specimens to no more than 61.0 mg,preferably 0.1 mg.11.6 Immerse the specimens in the test solution for 24 h.11.7 Remove the specimens, and rins
25、e with water whilebrushing with a stiff plastic bristle brush, for example, atoothbrush, to remove all adhering particles. Allow to air dry.11.8 Weigh the specimens and determine mass losses to nomore than 61.0 mg, preferably 0.1 mg. Reclean to obtain aconstant weight in accordance with Practice G1.
26、11.9 Calculate the mass losses per unit area and express asmg/cm2to the nearest whole number.NOTE 1OptionalTo ascertain the morphology of corrosion, thespecimen can be cross-sectioned, polished, and examined metallographi-cally after the mass loss determination.12. Report12.1 The report should conta
27、in the following information:12.1.1 Alloy identification,12.1.2 Product and temper of material,12.1.3 Sampling procedure particularly with respect to lo-cation in the product and the original material thickness,12.1.4 Mass loss per unit area,12.1.5 Any deviation in test procedure from that set forth
28、 inpreceding paragraphs,12.1.6 Solution volume to specimen surface area ratio,12.1.7 Specimen dimensions, and12.1.8 Number of specimens tested in each container.13. Precision and Bias13.1 Statement on Precision:13.1.1 Reproducibility of the mass loss results decreaseswith increased susceptibility to
29、 intergranular attack. Data onthe precision of test results obtained by this test method derivedfrom interlaboratory tests of 5086 and 5456 alloys are shown inASTM STP 516.3The standard deviations for test resultsamong six different laboratories ranged from 0.2 to 3.9 mg/cm2for resistant materials w
30、ith mean mass losses ranging from 1 to8 mg/cm2and from 5.5 to 6.6 mg/cm2for susceptible materialswith mean losses ranging from 30 to 44 mg/cm2(see Footnote4). The coefficient of variation is 0.3 6 0.1.13.1.2 The repeatability/variation within a laboratory isabout 0.05 coefficient of variation.13.1.3
31、 To provide an indication when some inadvertentdeviation from the correct test condition occurs, it is necessaryto expose to the test at regular intervals a control specimen ofa material with known resistance. This control should exhibitthe same degree of mass loss each time it is included in the te
32、st.13.1.4 The control may be any material of the alloy typeincluded in the scope of this test method, preferably one withan intermediate degree of susceptibility.13.2 BiasThe procedure in this test method has no biasbecause the value of mass loss due to intergranular corrosion isdefined only in term
33、s of this test method.G6713214. Keywords14.1 5xxx aluminum alloys; aluminum alloys; grain bound-ary sensitization; intercrystalline corrosion; intergranular cor-rosion; mass loss; nitric acid; pitting corrosionASTM International takes no position respecting the validity of any patent rights asserted
34、 in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the
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36、areful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM Internati
37、onal, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).G67133
