ASTM G34-2001(2018) Standard Test Method for Exfoliation Corrosion Susceptibility in 2XXX and 7XXX Series Aluminum Alloys (EXCO Test).pdf

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1、Designation: G34 01 (Reapproved 2018)Standard Test Method forExfoliation Corrosion Susceptibility in 2XXX and 7XXXSeries Aluminum Alloys (EXCO Test)1This standard is issued under the fixed designation G34; the number immediately following the designation indicates the year of originaladoption or, in

2、 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.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1

3、.1 This test method covers a procedure for constant im-mersion exfoliation corrosion (EXCO) testing of high-strength2XXX and 7XXX series aluminum alloys.NOTE 1This test method was originally developed for research anddevelopment purposes; however, it is referenced, in specific materialspecifications

4、, as applicable for evaluating production material (refer toSection 14 on Precision and Bias).1.2 This test method applies to all wrought products such assheet, plate, extrusions, and forgings produced from conven-tional ingot metallurgy process.1.3 This test method can be used with any form of spec

5、imenor part that can be immersed in the test solution.1.4 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, health, and environmental practices and deter-mine th

6、e applicability of regulatory limitations prior to use.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issu

7、ed by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterE3 Guide for Preparation of Metallographic SpecimensG15 Terminology Relating to Corrosion and Corrosion Test-ing (Withdrawn 2010)3G112 Guide f

8、or Conducting Exfoliation Corrosion Tests inAluminum Alloys2.2 ASTM Adjuncts:Illustrations (Enlarged Glossy Prints)43. Terminology3.1 Definitions:3.1.1 exfoliationcorrosion that proceeds laterally from thesites of initiation along planes parallel to the surface, generallyat grain boundaries, forming

9、 corrosion products that forcemetal away from the body of the material giving rise to alayered appearance (Terminology G15).4. Summary of Test Method4.1 This test method provides an accelerated exfoliationcorrosion test for 2XXX and 7XXX series aluminum alloysthat involves the continuous immersion o

10、f test materials in asolution containing 4 M sodium chloride, 0.5 M potassiumnitrate, and 0.1 M nitric acid at 25 6 3C (77 6 5F). Thesusceptibility to exfoliation is determined by visualexamination, with performance ratings established by refer-ence to standard photographs.5. Significance and Use5.1

11、 This test method was originally developed for researchand development purposes; however, it is referenced, inspecific material specifications, as applicable for evaluatingproduction material (refer to Section 14 on Precision and Bias).5.2 Use of this test method provides a useful prediction ofthe e

12、xfoliation corrosion behavior of these alloys in varioustypes of outdoor service, especially in marine and industrial1This 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.Current ed

13、ition approved Oct. 1, 2018. Published November 2018. Originallyapproved in 1972. Last previous edition approved in 2013 as G34 01 (2013). DOI:10.1520/G0034-01R18.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book

14、 of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.4Available from ASTM International Headquarters. Order Adjunct No.ADJG003402. Original adjunct produced in 1980.Co

15、pyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of Interna

16、tional Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1environments.5The test solution is very corrosive and repre-sents the more severe types of environmental service,excluding, of course, unusual chemicals not likely to been

17、countered in natural environments.5.3 The exfoliation ratings were arbitrarily chosen to illus-trate a wide range in resistance to exfoliation in this test.However, it remains to be determined whether correlations canbe established between EXCO test ratings and realistic serviceconditions for a give

18、n alloy. It is an ongoing activity of theTask Group on Exfoliation Corrosion of Aluminum Alloys(G01.05.02.08) to maintain outdoor exposure tests for thispurpose. For example, it has been reported6that samples ofAl-Zn-Mg-Cu alloys rated EAor P in a 48-h EXCO test did notdevelop more than a slight amo

19、unt of incipient exfoliation(EA) during six- to nine-year exposures to seacoastatmospheres, whereas, ED rated materials in most casesdeveloped severe exfoliation within a year in the seacoastatmosphere. It is anticipated that additional comparisons willbecome available as the outdoor tests are exten

20、ded.6. Apparatus6.1 Any suitable glass, plastic, or similarly inert containercan be used to contain the solution and specimens during theperiod of test. Depending upon the shape and size of thespecimens, rods or racks of glass, plastic, or any inert sub-stance shall be used to support the specimen a

21、bove the bottomof the container. The container should be fitted with a loose-fitting cover to reduce evaporation.7. Reagents7.1 Purity of ReagentsThe test solution shall be preparedwith reagent grade sodium chloride (NaCl), potassium nitrate(KNO3), and nitric acid (HNO3).7.2 Purity of WaterDistilled

22、 or deionized water shall beused to prepare test solution. The water purity must conform toSpecification D1193, Type IV reagent water, except that forthis method, the values of chloride and sodium can bedisregarded.7.3 A test solution of the following composition shall beused:NaCl (4.0 M)KNO3(0.5 M)

23、HNO3(0.1 M)Dissolve 234 g of NaCl, 50 g of KNO3in water, and add 6.3mL of concentrated HNO3(70 weight %). Dilute to 1 L. Thissolution has an apparent pH of 0.4.7.4 The solution shall be maintained at a temperature of 256 3C (77 6 5F).8. Sampling8.1 Sampling procedures are not considered applicable t

24、othis test method, as they are often covered by product specifi-cations. It is assumed that the test specimens are removed fromrepresentative samples of materials.9. Test Specimens9.1 Specimens may be of any practical size or shape.Nevertheless, for the results to be of most significance aspecimen s

25、ize of at least 50 by 100 mm (2 by 4 in.), or theequivalent, is recommended.9.2 The edges of sawed specimens need not be machined,but specimens obtained by blanking or shearing shall haveedges dressed by machining or filling to a depth equal to thethickness of the specimen to remove cold-worked meta

26、l.9.3 Remove the cladding of alclad sheet by machining thetest surface; remove or mask the cladding on the back side(non-test surface) also.9.4 When removing test specimens from extrusions andforgings, take care to avoid specimen locations underneathflanges, ribs, etc., where the grain structure is

27、usually variable.10. Standardization10.1 To provide an indication when some inadvertent de-viation from the correct test conditions 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 e

28、xfoliation each time it is included in thetest.10.2 The control may be any material of the alloy typeincluded in the scope of this test method, preferably one withan intermediate degree of susceptibility (Fig. 1 and Fig. 2).11. Procedure11.1 Degrease the specimens with a suitable solvent.11.2 Mask t

29、he back surfaces of the specimens to minimizecorrosion of non-test areas. Protective coatings must have goodadherence to avoid crevice corrosion beneath the coating; also,they should not contain leachable ions or protective oils thatwill influence the corrosion of the test surface. (See Figs. 1-6.)4

30、11.3 Use the solution in sufficient quantity to provide avolume-to-metal surface area ratio of 10 to 30 mL/cm2(65 to200 mL/in.2). Include all exposed metal area in the determina-tion of total surface area.11.4 Use fresh solution at the start of each test. Do notchange the solution even though the pH

31、 increases during thetest. It is normal for the pH to increase from the initial apparentvalue of 0.4 to about 3 during the first several hours dependingupon the amount of corrosion that occurs.11.5 Immerse the specimens in the solution using rods orracks of inert material to support the specimens ab

32、ove thebottom of the container. Place the test surface upward in a5Ketcham, S. J., and Jeffrey, P. W., “Exfoliation Corrosion Testing of 7178 and7075 Aluminum Alloys” (Report of ASTM G01.05 Interlaboratory Testing Programin Cooperation with the Aluminum Association); and Sprowls, D. O., Walsh, J. D.

33、,and Shumaker, M. B., “Simplified Exfoliation Testing of Aluminum Alloys,”Localized CorrosionCause of Metal Failure, ASTM STP 516, ASTM, 1972.6Sprowls, D. O., Summerson, T. J., and Loftin, F. E., “Exfoliation CorrosionTesting of 7075 and 7178 Aluminum AlloysInterim Report on AtmosphericExposure Test

34、s” (Report of ASTM G01.05.02 Interlaboratory Testing Program inCooperation with the Aluminum Association); and Lifka, B. W. and Sprowls, D. O.,“Relationship of Accelerated Test Methods for Exfoliation Resistance in 7XXXSeries Aluminum Alloys With Exposure to a Seacoast Atmosphere,” Corrosion inNatur

35、al Environments, ASTM STP 558, ASTM, 1974.G34 01 (2018)2Undermining pitting that may form the surface give the appearance of incipient exfoliation (Kellers Etch; 100).FIG. 1 Examples of Pitting CorrosionG34 01 (2018)3horizontal position to prevent loss of exfoliated metal from thesurface of the spec

36、imen. Do not concurrently immerse in thesame container alloys containing less than 0.25 % copper withthose containing greater amounts of copper.11.6 The following maximum periods of exposure arerecommended for testing the alloy types indicated:2XXX Series 96 h7XXX Series 48 hThe length of time to de

37、velop exfoliation in material of agiven alloy and temper may vary with the mill product form,with some materials developing severe exfoliation in muchshorter periods than those listed. Therefore, inspect test speci-mens in place and rate in accordance with Section 12 at periodssuch as 5, 24, 48, and

38、 72 h, and discontinue the exposure of aspecimen when it has developed the most severe exfoliationrating (Fig. 6).11.7 Rate the performance of test specimens in accordancewith Section 12 immediately after discontinuation of theexposure while the specimens are still wet or moist, taking intoaccount a

39、ll loose products of exfoliation lying on the testspecimen or on the bottom of the container.11.8 Clean exposed test specimens, if desired, by rinsing inwater and soaking in concentrated nitric acid after the speci-mens have been inspected and rated.12. Interpretation of Results12.1 The following co

40、des and classifications shall be usedwhen reporting the visual rating of corroded specimens:Classification CodeNo appreciable attack NPitting PExfoliation EA through EDExfoliation resulting from rapid lateral attack of selective boundaries or strata forming wedges of corrosion product that force lay

41、ers of metal upward giving rise to alayered appearance (Kellers Etch; 100).FIG. 2 Four Degrees of Severity of Exfoliation CorrosionG34 01 (2018)412.2 Descriptions of the various classifications, which areillustrated in Figs. 1-6,4are as follows:12.2.1 NNo appreciable attack: Surface may be discol-or

42、ed or etched, but no evidence of pitting or exfoliation.12.2.2 PPitting: Discrete pits, sometimes with a tendencyfor undermining and slight lifting of metal at the pit edges (Fig.1).12.2.3 EA through EDExfoliation (Figs. 1-6):12.2.3.1 Visible separation of the metal into layers mani-fested in variou

43、s forms, such as blisters, slivers, flakes, fairlycontinuous sheets, and sometimes granular particles resultingfrom disintegration of thin layers, depending upon the grainmorphology of the sample. Various degrees of exfoliation withincreasing penetration and loss of metal are illustrated in Fig.2. A

44、dditional examples of the various ratings are shown inFigs. 3-6.12.2.3.2 The formation of tiny pit-blisters or the dislodge-ment of an extremely thin surface layer of metal after only afew hours of exposure may resemble superficial exfoliation(EA), but can in fact result from undermining pitting. If

45、continued exposure to the recommended periods in 11.6produces more corrosion but no evidence of advancingFIG. 3 Examples of Exfoliation Rating EA (Superficial): Tiny Blisters, Thin Slivers, Flakes or Powder, with only Slight Separation ofMetalFIG. 4 Example of Exfoliation Rating EB (Moderate); Notab

46、le Layering and Penetration into the MetalG34 01 (2018)5delamination, metallographic examination (see Guide E3) willbe required to determine whether the initial effect was trulyexfoliation (Fig. 2) or undermining pitting (Fig. 1); in the lattercase the rating should be P.12.2.3.3 When exfoliation oc

47、curs in isolated sites, rate theworst localized condition observed.12.3 The visual ratings are intended to be finite indicationsof the resistance to exfoliation, and care should be taken whenrating a series of test specimens to compare them with thephotographs and captions in Figs. 1-6 rather than w

48、ith eachother. The final rating of a specimen shall be determined by thepoorest classification observed during the exposure.12.3.1 When it is difficult to classify a specimen, it isadvisable to place it in the category of greater susceptibility.NOTE 2Enlarged glossy prints of Figs. 1-6 are available

49、 from ASTMInternational.4These prints are more convenient to use and are of betterFIG. 5 Examples of Exfoliation Rating EC (Severe): Penetration to a Considerable Depth into the MetalFIG. 6 Examples of Exfoliation Rating ED (Very Severe) (Similar to EC Except for Much Greater Penetration and Loss of Metal)G34 01 (2018)6quality than the reproductions in the printed standard. The user is urged toobtain and use these prints.13. Report13.1 The report should contain the following essentialinformation:13.1.1 Alloy and temper of the material tested,13.1.2 Mill pro