1、Designation: G 34 01 (Reapproved 2007)Standard Test Method forExfoliation Corrosion Susceptibility in 2XXX and 7XXXSeries Aluminum Alloys (EXCO Test)1This standard is issued under the fixed designation G 34; the number immediately following the designation indicates the year of originaladoption or,
2、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.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1
3、 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 specim
5、enor 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 and health practices and determine the applica-bility of
6、 regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 1193 Specification for Reagent WaterE3 Guide for Preparation of Metallographic SpecimensG15 Terminology Relating to Corrosion and CorrosionTestingG112 Guide for Conducting Exfoliation Corrosion Tests inAluminum Alloys2
7、.2 ASTM Adjuncts:Illustrations (Enlarged Glossy Prints)33. Terminology3.1 Definitions:3.1.1 exfoliationcorrosion that proceeds laterally from thesites of initiation along planes parallel to the surface, generallyat grain boundaries, forming corrosion products that forcemetal away from the body of th
8、e 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 of test materials in asolution containing 4 M sodium chloride
9、, 0.5 M potassiumnitrate, and 0.1 M nitric acid at 25 6 3C (77 6 5F). Thesusceptibility to exfoliation is determined by visual examina-tion, with performance ratings established by reference tostandard photographs.5. Significance and Use5.1 This test method was originally developed for researchand d
10、evelopment 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 exfoliation corrosion behavior of these alloys in varioustype
11、s of outdoor service, especially in marine and industrialenvironments.4The test solution is very corrosive and repre-sents the more severe types of environmental service, exclud-ing, of course, unusual chemicals not likely to be encounteredin natural environments.5.3 The exfoliation ratings were arb
12、itrarily 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 given alloy. It is an ongoing activity of the1This test method is under th
13、e jurisdiction of ASTM Committee G01 onCorrosion of Metals and is the direct responsibility of Subcommittee G01.05 onLaboratory Corrosion Tests.Current edition approved May 1, 2007. Published May 2007. Originallyapproved in 1972. Last previous edition approved in 2001 as G 3401.2For referenced ASTM
14、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 Summary page onthe ASTM website.3Available from ASTM International Headquarters. Order Adjunct No.ADJG003402. Orig
15、inal adjunct produced in 1980.4Ketcham, 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.,and Shumaker, M. B., “Simplified Ex
16、foliation Testing of Aluminum Alloys,”Localized CorrosionCause of Metal Failure, ASTM STP 516, ASTM, 1972.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Task Group on Exfoliation Corrosion of Aluminum Alloys(G01.05.02.08) to maintai
17、n outdoor exposure tests for thispurpose. For example, it has been reported5that samples ofAl-Zn-Mg-Cu alloys rated EAor P in a 48-h EXCO test did notdevelop more than a slight amount of incipient exfoliation(EA) during six- to nine-year exposures to seacoast atmo-spheres, whereas, ED rated material
18、s in most cases developedsevere exfoliation within a year in the seacoast atmosphere. Itis anticipated that additional comparisons will become avail-able as the outdoor tests are extended.6. Apparatus6.1 Any suitable glass, plastic, or similarly inert containercan be used to contain the solution and
19、 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 above the bottomof the container. The container should be fitted with a loose-fitting cover to reduce evaporation.7.
20、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 or deionized water shall beused to prepare test solution. The water purity must conform toSpecification D 1193, Typ
21、e 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)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
22、 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 tothis test method, as they are often covered by product specifi-cations. It is assumed that the test specimens are
23、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 size of at least 50 by 100 mm (2 by 4 in.), or theequivalent, is recommended.9.2 The edges of sawed specimens need n
24、ot 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 metal.9.3 Remove the cladding of alclad sheet by machining thetest surface; remove or mask the cladding on the back sid
25、e(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 usually variable.10. Standardization10.1 To provide an indication when some inadvertent de-viation from the correct
26、 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 exfoliation each time it is included in thetest.10.2 The control may be any material of the alloy typeincluded in th
27、e 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 the back surfaces of the specimens to minimizecorrosion of non-test areas. Protective coatings must have goodadheren
28、ce 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.)311.3 Use the solution in sufficient quantity to provide avolume-to-metal surface area ratio of 10 to 30 mL/cm2(65 t
29、o200 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 increases during thetest. It is normal for the pH to increase from the initial apparentvalue of 0.4 to about 3 dur
30、ing 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 above thebottom of the container. Place the test surface upward in ahorizontal position to prevent loss of exfoliated
31、 metal from thesurface of the specimen. 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 S
32、eries 48 hThe length of time to develop 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 1
33、2 at periodssuch as 5, 24, 48, and 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 the5Sprowls, D. O., Summerson, T. J., and
34、Loftin, F. E., “Exfoliation CorrosionTesting of 7075 and 7178 Aluminum AlloysInterim Report on AtmosphericExposure Tests” (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 Meth
35、ods for Exfoliation Resistance in 7XXXSeries Aluminum Alloys With Exposure to a Seacoast Atmosphere,” Corrosion inNatural Environments, ASTM STP 558, ASTM, 1974.G 34 01 (2007)2Undermining pitting that may form the surface give the appearance of incipient exfoliation (Kellers Etch; 1003).FIG. 1 Examp
36、les of Pitting CorrosionG 34 01 (2007)3exposure while the specimens are still wet or moist, taking intoaccount all 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 n
37、itric acid after the speci-mens have been inspected and rated.12. Interpretation of Results12.1 The following codes and classifications shall be usedwhen reporting the visual rating of corroded specimens:Classification CodeNo appreciable attack NPitting PExfoliation EA through ED12.2 Descriptions of
38、 the various classifications, which areillustrated in Figs. 1-6,3are as follows:12.2.1 NNo appreciable attack: Surface may be discol-ored or etched, but no evidence of pitting or exfoliation.12.2.2 P Pitting: Discrete pits, sometimes with a tendencyfor undermining and slight lifting of metal at the
39、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 various forms, such as blisters, slivers, flakes, fairlycontinuous sheets, and sometimes granular particles resultingfrom disintegration of thin layers, depending upon th
40、e grainmorphology of the sample. Various degrees of exfoliation withincreasing penetration and loss of metal are illustrated in Fig.2. Additional 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
41、of metal after only afew hours of exposure may resemble superficial exfoliation(EA), but can in fact result from undermining pitting. Ifcontinued exposure to the recommended periods in 11.6Exfoliation resulting from rapid lateral attack of selective boundaries or strata forming wedges of corrosion p
42、roduct that force layers of metal upward giving rise to alayered appearance (Kellers Etch; 1003).FIG. 2 Four Degrees of Severity of Exfoliation CorrosionG 34 01 (2007)4produces more corrosion but no evidence of advancing delami-nation, metallographic examination (see Guide E3) will berequired to det
43、ermine 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 occurs in isolated sites, rate theworst localized condition observed.12.3 The visual ratings are intended to be finite indicationsof the
44、 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 with eachother. The final rating of a specimen shall be determined by thepoorest classification observed during the exposure.12.3.1 Whe
45、n 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 from ASTMInternational.3These prints are more convenient to use and are of betterFIG. 3 Examples of Exfoliation Rating EA (Superficia
46、l): Tiny Blisters, Thin Slivers, Flakes or Powder, with only Slight Separation ofMetalFIG. 4 Example of Exfoliation Rating EB (Moderate); Notable Layering and Penetration into the MetalG 34 01 (2007)5quality than the reproductions in the printed standard. The user is urged toobtain and use these pri
47、nts.13. Report13.1 The report should contain the following essentialinformation:13.1.1 Alloy and temper of the material tested,13.1.2 Mill product, section thickness, and the surfacetested, including reference to applicable product specification,13.1.3 Sampling procedure if other than that specified
48、 inreferenced product specification,13.1.4 A rating of the test specimens using the codes andclassifications in Section 12, and13.1.5 Notation of any deviation in test procedure from thatset forth in preceding paragraphs.13.2 Other information that may be desirable for certaintypes of reports includ
49、es:13.2.1 Size, type, and number of replicate specimens;method of edge preparation, and13.2.2 Volume to surface ratio.FIG. 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)G 34 01 (2007)614. Precision and Bias14.1 Precision:14.1.1 The precision of the data from this test method wasevaluated by way of an interlaboratory test program using twonon-commercial tempers of Alloy 7075 with different l
