1、Designation: G67 18Standard 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, also known as the Nitric Aci
3、d MassLoss Test (NAMLT) describes a procedure for constant immer-sion intergranular corrosion testing of 5XXX series aluminumalloys.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.
4、1.4 The values stated in SI units are to be regarded 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 app
5、ro-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 theD
6、evelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterE29 Practice for Using Significant Digits in Test Data toDetermine Conf
7、ormance with SpecificationsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodG1 Practice for Preparing, Cleaning, and Evaluating Corro-sion Test SpecimensG16 Guide for Applying Statistics to Analysis of CorrosionData3. Summary of Test Method3.1 This test
8、 method consists of immersing test specimensin 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 interg
9、ranular corrosion of Al-Mg and Al-Mg-Mn alloys. The 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 bound
10、aries, the effect of thepreferential attack 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/in.2), whereas, samples ofintergranular-resistant materials lose o
11、nly about 1 to 15 mg/cm2(10 to 100 mg/in.2). When the 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
12、precipitation of the second phase in the grainboundaries 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 up
13、on the degree of precipitate continuity inthe grain boundaries. Visible manifestations of the attack may1This 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 develo
14、ped by a joint task group withThe Aluminum Association, Inc.Current edition approved Oct. 1, 2018. Published January 2019. Originallyapproved in 1980. Last previous edition approved in 2013 as G67 13. DOI:10.1520/G0067-18.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontac
15、t ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standar
16、d was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1be in va
17、rious 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 cleaningafter exposure, the mass loss will be low relative to th
18、e 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 individualbeakers for each specimen is recommended; however, theimmersion of multip
19、le 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, specimens should be isolated electricallyfrom one another. A recommended method of positioning thespecime
20、ns is to incline them so that the edges rest on thebottom and side wall of the container. See Figs. 1 and 2 for anexample of the recommended configuration, using a 100 mLnon-fluted beaker and a watchglass cover for each specimenwith the beakers immersed in a water bath. This method isconsidered to b
21、e the optimal configuration for this testmethod.46.1.2 The container should have a loose fitting cover toreduce evaporation and to confine any fumes evolved by theacid.6.2 Laboratory-Grade Water BathThis test method re-quires precise temperature control (see 8.2 for tolerances ontest temperature). I
22、t is highly recommended that a laboratory-grade water bath be used. An ideal configuration of specimensand water bath are shown in Figs. 1 and 2.6.3 Temperature Measuring DeviceGiven the extremesensitivity to temperature fluctuations, it is recommended thatthe temperature be measured continuously wi
23、th a recordingtemperature measurement device.6.4 Ultrasonic BathThe corroded specimens will becleaned using an ultrasonic cleaning bath (see 11.7). Suchultrasonic cleaning baths are available from all of the commonlaboratory supply companies and typically have an operatingfrequency of 40 kHz and 15
24、to 50 W/L ultrasonic power.7. Reagents7.1 Purity of ReagentsThe nitric acid (HNO3) test solu-tion shall be reagent grade within the range of 67 to 70 w/w %.The sodium hydroxide (NaOH) solution used for etching andthe HNO3(67 to 70 w/w %) used for desmutting shall also bereagent grade.7.2 Purity of W
25、aterUse water conforming to SpecificationD1193 Type IV to prepare the NaOH solution and for rinsingand ultrasonic cleaning purposes.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/m2(19 mL/in.2).8
26、.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 dimensions 50 mm by 6 mm
27、(2in. by 0.25 in.) by product thickness. The 50-mm dimensionshall be parallel to the longitudinal direction of the product.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, 19
28、72, pp. 1737.4Aluminum Association Technical Report T1, “Exfoliation Corrosion Testing ofAluminum Alloys 5086 and 5456,” T.J. Summerson, D.O. Sprowls. Published circa1975. Currently out-of-print. Hard copies can be acquired from the AluminumAssociation.FIG. 1 Recommended Configuration for Specimen E
29、xposure; A 100 mL Non-fluted Beaker and WatchglassG6718210.2 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-fabricated surface. All sawn surfacesshall be machined to the final dimensions.10.3 A small
30、drilled hole (3.5 % Mg)5XXX alloy, and expose it at elevated temperature (100C(212F) is most commonly used) for varying times, to obtain acondition that gives a mass loss value on the order of 20 to 30mg/cm2. Actual times will vary for different alloys andtempers. The user should then run this contr
31、ol specimen withevery test batch, and develop a performance band of theaverage of ten or more sequential readings 6 two standarddeviations. For any given test batch, a measurement for thecontrol material that is outside of the established performanceband would be an indication of a problem with that
32、 test. Thebatch should be re-run once the problem is identified andresolved.13. Report13.1 The report should contain the following information:13.1.1 Alloy identification,13.1.2 Product and temper of material,13.1.3 Sampling procedure particularly with respect to lo-cation in the product and the ori
33、ginal material thickness,13.1.4 Mass loss per unit area,13.1.5 Any deviation in test procedure from that set forth inpreceding paragraphs,13.1.6 Solution volume to specimen surface area ratio,13.1.7 Specimen dimensions, and13.1.8 Number of specimens tested in each container.14. Precision and Bias14.
34、1 Statement on Precision:14.1.1 The precision of the data for this test method wasevaluated by way of an interlaboratory test program conductedin accordance with Practice E691. Round robin testing wasconducted using non-commercial tempers of Alloy 5086 withdifferent levels of intergranular corrosion
35、 susceptibility. Ninelaboratories participated in the round robin test program. Thelaboratories received machined specimens, which theyweighed and exposed according to the procedure in this testmethod. Analysis of the round robin results was carried outusing the procedures shown in Guide G16 for ave
36、rage, stan-dard deviation and coefficient of variation. Additional detailson the interlaboratory test program are documented in Re-search Report RR:G01-1028.65These standard samples are available from Metal Samples, 152 Metal SamplesRd., Munford, AL 36268.6Supporting data have been filed at ASTM Int
37、ernational Headquarters and maybe obtained by requesting Research Report RR:G01-1028. ContactASTM CustomerService at serviceastm.org.G6718414.1.2 The reproducibility coefficient of variation wasgreater for specimens showing greater mass loss, that is, thereproducibility decreased for specimens with
38、greater suscepti-bility to intergranular attack. The standard deviations for testresults among nine different laboratories ranged from 0.34 to0.36 mg/cm2for materials with average mass losses rangingfrom 2.6 to 3.3 mg/cm2, from 2.1 to 5.2 mg/cm2for materialswith average mass losses ranging from 11.0
39、 to 24.5 mg/cm2,and from 10.7 to 10.8 mg/cm2for materials with average masslosses ranging from 40.6 to 41.2 mg/cm2. The reproducibilitycoefficients of variation ranged from 10 to 26 %.14.1.3 The coefficient of variation of the repeatability re-sults in the round robin was 4 %.14.2 BiasBias statement
40、s are only applicable for testmethods which utilize known reference standards. The value ofmass loss due to intergranular corrosion is defined only interms of this test method, hence a bias statement does notapply.15. Keywords15.1 5xxx aluminum alloys; aluminum alloys; grain bound-ary sensitization;
41、 intercrystalline corrosion; intergranular cor-rosion; mass loss; nitric acid; pitting corrosionASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determin
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