1、Designation: B940 05 (Reapproved 2009)1Standard Practice forTesting Non-Chromate Coatings on Zinc and CadmiumSurfaces1This standard is issued under the fixed designation B940; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the yea
2、r of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1NOTEThe units statement in subsection () wa
3、s added editorially in January 2010.1. Scope1.1 This practice covers a procedure for evaluating theprotective value of chemical and electrochemical conversioncoatings produced by non-chromate (chromate being defined asa compound that has chromium in the plus six oxidation state,and as such, chromium
4、 compounds in other oxidation states,such as plus three, shall not be excluded) treatments of zinc andcadmium surfaces.1.2 The protective value of a non-chromate coating isusually determined by salt-spray test and by determiningwhether or not the coating possesses adequate abrasion resis-tance when
5、applied for that purpose.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.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 s
6、tandard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2B117 Practice for Operating Salt Spray (Fog) Apparatus3. Terminology3.1 Descriptions of Terms:3.1.1 time to failuretime to
7、failure will depend on the typeof coating tested. The minimum expected protective valueobtainable in a given salt spray test is given 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 unaide
8、d eye at normal reading distance,except that the presence of white corrosion 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 fa
9、ilure.3.1.2 significant surfacesin general, significant surfacesare those surfaces 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
10、 be indicatedon the drawing.4. Significance and Use4.1 This practice is applicable to non-chromate coatings thatare colorless, colored, electrochemically applied or non-electrochemically applied. The zinc or cadmium, or both, maybe electrodeposited, mechanically deposited, hot-dipped,rolled, or in t
11、he form of castings.4.2 Because of variables inherent in the salt-spray testwhich may differ from one test cabinet to another, interpreta-tion of test results for compliance with expected performanceshould be specified by the purchaser.4.3 Properties such as thickness, color, luster, and ability top
12、rovide 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 AgingBefore subjecting a non-chromate coating totest, check with the chemical producer to determine if aging isan issue that needs to be co
13、nsidered.1This practice is under the jurisdiction of ASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.07 onConversion CoatingsCurrent edition approved Sept. 1, 2009. Published January 2009. Originallyapproved in 2000. Last previous edition app
14、roved in 2005 as B940 05. DOI:10.1520/B0940-05R09E01.2For 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 Summary page onthe ASTM website.1Copyrig
15、ht ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.2 Preparation of SpecimenThe test surface must be freeof fingerprints and other extraneous stains and must not becleaned except by gentle wiping with a clean, dry, soft cloth toremove loose p
16、articles. Oily or greasy surfaces should not beused for testing, and degreasing with organic solvents is notrecommended.6. Procedure6.1 Salt Spray TestExpose the clean specimen to a 5 %solution salt spray and conduct the test in accordance with thelatest revision of Practice B117. Unless otherwise s
17、pecified,only those surfaces that are positioned in the test chamber inaccordance with Practice B117 are considered pertinent forevaluating failure. The exposed surfaces of the test specimensshall be free of all visible defects, such as scratches or pits, orboth, and shall be flat. The surfaces shal
18、l not be cleaned withabrasive materials or abrasive chemical agents that may etchthe exposed surfaces. Corrosion found on surfaces within14 ofan inch of the edges of the exposed specimens shall not beconsidered significant to the test.6.2 Abrasion Resistance TestFor those non-chromatedcoatings desig
19、ned and specified by the chemical producer asabrasion-resistant, rub the non-chromated surface with a grit-less, soft gum eraser (art-gum) for 2 to3sbyhand (about tenstrokes) using normal pressure (about 70 kPa (10 psi) and astroke approximately 50 mm long. The non-chromate coatingshould not be remo
20、ved or worn through to the underlying metalas a result of this treatment.7. Keywords7.1 non-chromate coatingsAPPENDIXES(Nonmandatory Information)X1. NATURE OF COATINGSX1.1 The primary purpose of non-chromate finishes used asa replacement for chromate finishes is to retard the formationof white corro
21、sion products upon exposure to stagnant water,moist atmosphere, or stagnant environments containing or-ganic vapors, such as may emanate from certain plastics,paints, and other organic materials. These finishes will notprevent the growth of metallic filaments, commonly known as“whiskers.”X1.2 Coatin
22、gs covered by this practice generally containoxides of the basis metal in varying proportions. They may beproduced by either chemical or electrochemical processes fromsolutions free of hexavalent chromium compounds.X1.3 The quality of the non chromate film depends to alarge extent on the chemical pu
23、rity and the physical conditionof the basis surface to which it is applied. In order to producean acceptable coating, it is essential that the surface be properlycleaned and free of heavy metallic impurities such as lead, orcopper, which may interfere with the proper formation of thecoating.X1.4 The
24、 color and luster produced by a given treatmentwill depend to some extent on the surface condition of themetal to which it is applied and may vary from part to part, oreven on one single part.X2. PROTECTION BY NON-CHROMATE COATINGSX2.1 The minimum degree of protection that can beexpected from non-ch
25、romate coatings on electrodeposited zincwhen subjected to a 5 % salt spray test is 12 h.X2.2 This value is given for guidance purposes only and isnot to be construed as endpoint requirements. All types of zincand cadmium coatings can be non-chromated, and there may ormay not be differences in the pr
26、otection afforded by thenon-chromate, depending on the type of coating and themethod of processing, so the actual protection required shouldbe established to the satisfaction of the manufacturer and thepurchaser.B940 05 (2009)12ASTM International takes no position respecting the validity of any pate
27、nt rights asserted in connection with any item mentionedin 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
28、at any time by the responsible technical committee and must 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 comme
29、nts will receive careful consideration at a meeting of theresponsible 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
30、 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). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).B940 05 (2009)13
