1、Designation: B 940 05Standard Practice forTesting Non-Chromate Coatings on Zinc and CadmiumSurfaces1This standard is issued under the fixed designation B 940; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisio
2、n. 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 for use by agencies of the Department of Defense.1. Scope1.1 This practice covers a procedure for evaluating
3、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 compounds in other oxidation states,such as plus three, shall not be excluded) treatments of zi
4、nc 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 applied for that purpose.1.3 This standard does not purport to address all of thesafety concerns
5、, 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 regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2B117 Practice for Operating Salt Spray (Fog
6、) Apparatus3. Terminology3.1 Descriptions of Terms:3.1.1 time to failuretime to 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 app
7、earance on significant surfaces of white corrosionproducts visible to the unaided 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
8、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 surfaces that are visible and subject to corrosion orwear, or both, except that surfaces that are normally difficult tocoat by electroplating or m
9、echanical deposition may be ex-empt. The designation of significant surfaces may 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
10、both, maybe electrodeposited, mechanically deposited, hot-dipped,rolled, or in the 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 b
11、y 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 AgingBefore subjecting a non-chromate coating totest, check
12、 with the chemical producer to determine if aging isan issue that needs to be considered.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 particles. Oily or
13、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 specified,only thos
14、e surfaces that are positioned in the test chamber inaccordance with Practice B117 are considered pertinent for1This practice is under the jurisdiction of ASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.07 onChromate Conversion Coatings.Curre
15、nt edition approved Oct. 1, 2005. Published October 2005.2For 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.1Cop
16、yright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.evaluating 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 shall not be cleaned w
17、ithabrasive 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 designed and specified
18、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 removed or worn throug
19、h 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 corrosion products upon
20、 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 Coatings covered by this
21、 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 purity and the physi
22、cal 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 color and luster
23、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-chromate coatings on
24、 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 protection afforded
25、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.ASTM International takes no position respecting the validity of any patent rights asserted in connection w
26、ith 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 at any time by the responsible tec
27、hnical 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 comments will receive careful considera
28、tion 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 by ASTM International, 100 Barr H
29、arbor 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).B940052
