ASTM B201-1980(2004) Standard Practice for Testing Chromate Coatings on Zinc and Cadmium Surfaces《锌和镉的表面铬酸盐覆层试验》.pdf

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1、Designation: B 201 80 (Reapproved 2004)Endorsed by AmericanElectroplaters SocietyEndorsed by NationalAssociation of Metal FinishersStandard Practice forTesting Chromate Coatings on Zinc and Cadmium Surfaces1This standard is issued under the fixed designation B 201; the number immediately following t

2、he designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved fo

3、r use by agencies of the Department of Defense.1. Scope1.1 This practice covers a procedure for evaluating theprotective value of chemical and electrochemical conversioncoatings produced by chromate treatments of zinc and cad-mium surfaces.1.2 The protective value of a chromate coating is usuallydet

4、ermined by salt-spray test and by determining whether ornot the coating possesses adequate abrasion resistance.1.3 Other methods, such as exposure to a humidity environ-ment, can be used, but are generally of too long a duration tobe of practical value. “Steam Tests” using pressure cookershave also

5、been used for testing chromate films on hot-dipgalvanized surfaces.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 ap

6、plica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:B 117 Practice for Operating Salt Spray (Fog) Apparatus23. Terminology3.1 Descriptions of Terms:3.1.1 time to failuretime to failure will depend on the typeof coating tested. A list of some expected protect

7、ive valuesobtainable in a given salt spray test is shown in Appendix X2.3.1.1.1 DiscussionIn most instances, failure is defined asthe first appearance on significant surfaces of white corrosionproducts visible to the unaided eye at normal reading distance,except that the presence of white corrosion

8、products at sharpedges (for example, on threaded fasteners) and at junctionsbetween dissimilar metals should not be considered failure. Insome instances, it may be desirable to regard the first appear-ance of red rust as failure.3.1.2 significant surfacesin general, significant surfacesare those sur

9、faces that are visible and subject to corrosion orwear, or both, except that surfaces that are normally difficult tocoat by electroplating or mechanical deposition may be ex-empt. The designation of significant surfaces may be indicatedon the drawing.4. Significance and Use4.1 This practice is appli

10、cable to chromate coatings of thecolorless (both one and two-dip), iridescent yellow or bronze,olive drab, black, colorless anodic, yellow or black anodictypes, and of the dyed variety, when applied to surfaces ofelectrodeposited zinc, mechanically deposited zinc, hot-dippedzinc, rolled zinc, electr

11、odeposited cadmium, mechanicallydeposited cadmium, and zinc die castings.NOTE 1Colorless coatings are also referred to as clear-bright orblue-bright coatings.4.2 Because of variables inherent in the salt-spray test,which may differ from one test cabinet to another, interpreta-tion of test results fo

12、r compliance with expected performanceshould be specified by the purchaser.4.3 Properties such as thickness, color, luster, and ability toprovide good paint adhesion are not covered in this practice,nor are the chemical composition and the method of applica-tion of these finishes.5. Conditioning5.1

13、AgingBefore subjecting a chromate coating to test, itmust be aged at room temperature in a clean environment forat least 24 h after the chromating treatment.5.2 Preparation of SpecimenThe test surface must be freeof fingerprints and other extraneous stains and must not becleaned except by gentle wip

14、ing with a clean, dry, soft cloth toremove loose particles. Oily or greasy surfaces should not beused for testing, and degreasing with organic solvents is notrecommended.1This practice is under the jurisdiction of ASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility

15、of Subcommittee B08.07 onChromate Conversion Coatings.Current edition approved Oct. 1, 2004. Published October 2004. Originallyapproved in 1945. Last previous edition approved in 2000 as B 201 80 (2000).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Ser

16、vice at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6. Procedure6.1 Salt Spray TestExpose the c

17、lean specimen to a 5 %solution salt spray and conduct the test in accordance with thelatest revision of Practice B 117. Unless otherwise specified,only those surfaces that are positioned in the test chamber inaccordance with Practice B 117 are considered pertinent forevaluating failure.6.2 Abrasion

18、Resistance TestTo determine whether thecoating is adherent, nonpowdery, and abrasion resistant, rubthe chromated surface with a gritless, soft gum eraser (art-gum)for2to3sbyhand (about ten strokes) using normal pressure(about 70 kPa (10 psi) and a stroke approximately 50 mmlong. The chromate coating

19、 should not be removed or wornthrough to the underlying metal as a result of this treatment.6.3 Test for Colorless (Clear) CoatingsThis test appliesonly to coatings that are free of secondary supplementarycoatings, such as oil, water or solvent-based polymers, or wax.6.3.1 Determine the presence of

20、a colorless (clear) coatingby placing a drop of lead acetate testing solution on the surface.Allow the drop to remain on the surface for 5 s. Remove thetesting solution by blotting gently, taking care not to disturbany deposit that may have formed. A dark deposit or black stainis indicative of the a

21、bsence of a coating.6.3.2 Prepare the test solution by dissolving 50 g of leadacetate trihydrate (Pb(C2H3O2)23H2O) in 1 L of distilled ordeionized water. The pH of the solution should be between 5.5and 6.8. Any white precipitate formed during the initialpreparation of the solution may be dissolved b

22、y small additionsof acetic acid; provided that the pH is not reduced to a valuebelow 5.5. Upon formation of a white precipitate thereafter, thesolution should be discarded.6.3.3 For comparative purposes, treat an untreated surfacesimilarly. On an untreated surface, a black spot forms almostimmediate

23、ly.APPENDIXES(Nonmandatory Information)X1. NATURE OF COATINGSX1.1 The primary purpose of chromate finishes is to retardthe formation of white corrosion products upon exposure tostagnant water, moist atmosphere, or stagnant environmentscontaining organic vapors, such as may emanate from certainplasti

24、cs, paints, and other organic materials. Chromate finisheswill not prevent the growth of metallic filaments, commonlyknown as “whiskers.”X1.2 Coatings covered by this practice generally containoxides of the basis metal and tri- and hexavalent chromium invarying proportions, except that colorless coa

25、tings containlittle or no hexavalent chromium. They may be produced byeither chemical or electrochemical processes from solutionscontaining hexavalent chromium compounds with one or moreof certain anions which act as activators, film formers or both.There is evidence that over an extended period, ch

26、romatecoatings undergo some chemical changes even under ordinaryconditions. These changes increase with increase in tempera-ture. At temperatures above approximately 65C, thesechanges take place fairly rapidly, converting the solublehexavalent chromium ion into an insoluble compound andthereby reduc

27、ing its protective value under salt spray andhumid conditions. Colorless or light iridescent coatings appearto be less sensitive to elevated temperatures than are heavychromate coatings.X1.3 The quality of the chromate film depends to a largeextent on the chemical purity and the physical condition o

28、f thebasis surface to which it is applied. In order to produce anacceptable coating, it is essential that the surface be properlycleaned and free of heavy metallic impurities such as lead,copper, and contamination (specific for zinc), such as bright-ener occlusions, and oxides, which interfere with

29、the chromat-ing reaction.X1.4 The thickness of the coating to be chromated shouldbe not less than 5.0 m and the thickness requirement on thecoating and chromated finish should apply after the chromatetreatment. The color and luster produced by a given treatmentwill depend to some extent on the surfa

30、ce condition of themetal to which it is applied and may vary from part to part, oreven on one single part.X2. PROTECTION BY CHROMATE COATINGSX2.1 Table X2.1 illustrates the minimum degree of protec-tion that can be expected from the various types of chromatecoatings on electrodeposited zinc when sub

31、jected to a 5 % saltspray test.X2.2 These values are shown for guidance purposes onlyand are not to be construed as endpoint requirements. All typesof zinc and cadmium coatings can be chromated, and there mayor may not be differences in the protection afforded by thechromate depending on the type of

32、 coating and the method ofprocessing, so the actual protection required should be estab-lished to the satisfaction of the manufacturer and the purchaser.B 201 80 (2004)2ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin

33、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 responsible technical committee and must

34、 be reviewed every five 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 ther

35、esponsible 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 International, 100 Barr Harbor Drive, PO Box C700,

36、 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).TABLE X2.1 Expected ProtectionType of CoatingExpected MinimumHours to WhiteCorrosion of ZincOne-dip colorless (clear bright) 12Two-dip colorless (clear bright) 24Black dip 48Anodic-colorless 48Anodic-black 96Iridescent yellow or bronze 96Anodic-yellow 150Olive-drab 150B 201 80 (2004)3