1、Designation: G 67 04Standard 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 G 67; the number immediately following the designation indica
2、tes 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method describes a procedure for
3、constantimmersion 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
4、 as 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
5、the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 1193 Specification for Reagent WaterG 1 Practice for Preparing, Cleaning, and Evaluating Cor-rosion Test Specimens3. Summary of Test Method3.1 This test method consists of immersing test specimensi
6、n concentrated 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 alloy
7、s. The nitric acid dissolves a second phase, analuminum-magnesium intermetallic compound (bAl-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
8、is to 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). W
9、hen the bAl-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 grai
10、nboundaries also gives rise to intergranular corrosion when thematerial is exposed to chloride-containing natural environ-ments, such as seacoast atmospheres or sea water. The extent towhich the alloy will be susceptible to intergranular corrosiondepends upon the degree of precipitate continuity in
11、the grainboundaries. Visible manifestations of the attack may be invarious forms such as pitting, exfoliation, or stress-corrosioncracking, depending upon the morphology of the grain struc-ture and the presence of sustained tensile stress.35. Interferences5.1 If all loose particles are not removed d
12、uring cleaningafter 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 andspecimens during the period of the test. The use of individual1Th
13、is test method is under the jurisdiction of ASTM Committee G01 onCorrosion 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, 2004. Published
14、 May 2004. Originallyapproved in 1980. Last previous edition approved in 1999 as G 67 99.2For 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 Document Summ
15、ary 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, pp. 1737, 1972.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohock
16、en, PA 19428-2959, United States.beakers 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 major surfaces is in total contact with the wallsof the container. Also
17、, 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 loose fitting cover toreduce evaporation and to confine any fumes evol
18、ved 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 used for etching and the HNO3(70to 72 weight %) used for desmutting sh
19、all also be reagentgrade.7.2 Purity of WaterUse water conforming to SpecificationD 1193 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 constitute a volume to specimen surface area ratio ofat least 30 L
20、/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 this standard.10. Test Specimens10.1 Prepare specimens with dimension
21、s 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 25 mm, whichever is less, whileretaining one original as-fabricate
22、d 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 can be achieved by eitherscribing or stamping. Confine identificat
23、ion 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 water rinse, a 30-s immersionin HNO3(desmut), and a water rinse.
24、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 rinse with water whilebrushing with a stiff plastic bristle brush, for
25、 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 G 1.11.9 Calculate the mass losses per unit area and express asmg/cm2
26、to 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 contain the following information:12.1.1 Alloy identification,12.1.2 P
27、roduct 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 inpreceding paragraphs,12.1.6 Solution volume to specimen surfac
28、e 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 intergranular attack. Data onthe precision of test results obtai
29、ned 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 with mean mass losses ranging from 1 to8 mg/cm2and from 5.5 to 6.6
30、 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 To provide an indication when some inadvertentdeviation from the
31、 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 test.13.1.4 The control may be any material of the alloy typeinclud
32、ed 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 terms of this test method.14. Keywords14.1 5xxx aluminum alloys; alum
33、inum alloys; grain bound-ary sensitization; intercrystalline corrosion; intergranular cor-rosion; mass loss; nitric acid; pitting corrosionG67042ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of
34、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 responsible technical committee and must be reviewed every five
35、years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical com
36、mittee, 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 International, 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).G67043
