1、Designation: B 921 02Standard Specification forNon-hexavalent Chromium Conversion Coatings onAluminum and Aluminum Alloys1This standard is issued under the fixed designation B 921; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, th
2、e 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.1. Scope1.1 This specification covers the requirements relating torinsed and non-rinsed non-hexavalent chromium convers
3、ioncoatings on aluminum and aluminum alloys intended to giveprotection against corrosion and as a base for other coatings.1.2 Aluminum and aluminum alloys are conversion coatedin order to retard corrosion; as a base for organic filmsincluding paints, plastics, and adhesives; and as a protectivecoati
4、ng having a low electrical contact impedance.1.3 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 regula
5、tory requirements prior to use.2. Referenced Documents2.1 ASTM Standards:B 117 Practice for Operating Salt Spray (Fog) Apparatus2B 602 Test Method for Attribute Sampling of Metallic andInorganic Coatings3D 1730 Practices for Preparation of Aluminum andAluminum-Alloy Surfaces for Painting3D 3359 Test
6、 Methods for Measuring Adhesion by TapeTest42.2 ISO Standards:ISO 2409 Paint and VarnishesCross-Cut Test5ISO 3768 Metallic CoatingsNeutral Salt Spray Test (NSSTest)5ISO 4519 Electrodeposited Metallic Coatings and RelatedFinishesSampling Procedures for Inspection by At-tributes52.3 Federal Standard:F
7、ed. Std. No. 141 Paints, Varnish, Lacquer, and RelatedMaterials; Methods of Inspection62.4 Military Specification:MIL-C-5541 Chemical Films for Aluminum and AluminumAlloys63. Terminology3.1 Definitions:3.1.1 non-rinsedconversion coatings that are dried imme-diately after the conversion coating step
8、without receiving awater rinse.3.1.1.1 DiscussionThis special type of coating is typicallyused on long coils of aluminum sheet stock that receive animmediate subsequent paint or adhesive coating.NOTE 1Non-rinsed conversion coatings are finding increased usageon fabricated parts and castings.3.1.2 ri
9、nsedconversion coatings that are rinsed in waterprior to drying.3.1.2.1 DiscussionThis type of coating is typically ap-plied to extruded aluminum fabricated parts and castings.4. Classification4.1 A class one conversion coating provides for maximumsalt fog corrosion protection to bare metal. A class
10、 twoconversion coating is designed to give painted salt fog corro-sion resistance and some bare salt fog corrosion resistance. Aclass three conversion coating provides little salt fog corrosionresistance, but low electrical contact resistance (see MIL-C-5541). Class four and five conversion coatings
11、 only provide forpainted salt fog corrosion resistance.4.2 The finishes are divided into four classes; their mostimportant characteristics are listed in Table 1.5. Surfaces Preparation5.1 The surfaces of the parts to be conversion coated shallbe clean and free of any oxidation, scale, or soils such
12、as metalturnings, grinding dust, oil, grease, lubricants, hand-sweat, orany other contamination detrimental to the conversion coatingprocess. The parts shall therefore, as far as necessary, be1This specification is under the jurisdiction of ASTM Committee B08 onMetallic and Inorganic Coatings and is
13、 the direct responsibility of SubcommitteeB08.07 on Chromate Conversion Coatings.Current edition approved Sept. 10, 2002. Published November 2002.2Annual Book of ASTM Standards, Vol 03.02.3Annual Book of ASTM Standards, Vol 02.05.4Annual Book of ASTM Standards, Vol 06.01.5Available from American Nat
14、ional Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.6Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428
15、-2959, United States.cleaned in a non-hexavalent chromium cleaner before conver-sion coating and, if necessary, be pickled.6. Methods of Application of Conversation Coatings6.1 Metallic material other than aluminum shall not betreated with the parts to be conversion coated.6.2 Conversion coatings ar
16、e normally applied by dipping:the coating may also be applied by inundation, spraying, rollercoating, or by wipe-on techniques. The application methodused shall be taken from the operating instructions for theconversion coating process employed. Conversion coatingsolutions are usually acidic and may
17、 contain various salts thatmay be varied to affect the appearance and hardness of the film.The type of conversion coating depends on the composition ofthe solution and may also be affected by the pH, temperature,duration of the treatment, and the nature and surface conditionof the alloy being treate
18、d.6.3 Those coatings receiving a final water rinse. If thecoating is meant to be a basis for additional coatings, the detailshall be subject to a rinse in deionized water with a conduc-tivity less than 100t S/cm. Hot water shall be used only ifallowed by the manufacturer of the conversion coating in
19、question. The drying of the coating shall be carried out inaccordance with the specifications of the manufacturer of theconversion or conversion coating in question.6.4 Any additional subsequent treatments will depend uponthe direction of the manufacture of the conversion or conver-sion coating in q
20、uestion.7. Coating Requirements7.1 Electrical ResistanceWhen specified, the electricalresistance shall be in accordance with MIL-C-5541.7.2 AdhesionThe coatings shall be adherent and non-powdery. A practical evaluation of the adhesion can be madeby measuring the adhesion of a secondary organic film
21、appliedto the conversion coating in question. When specified, theconversion coating shall pass the organic coating adhesion testin Test Methods D 3359 or the equivalent ISO 2409.7.2.1 Class 4 coatings intended for use under MIL-C-5541shall have their adhesion evaluated by Method 6301 of Fed.Std. No.
22、 141.7.2.2 Additional treatments applied under MIL-C-5541 canbe found in Practices D 1730, Methods 5, 6, and 7.7.3 Corrosion ResistanceWhen subjected to the neutralsalt spray test specified in Test Method B 117 or in theequivalent ISO 3768, three separate test specimens of thecoating shall withstand
23、 exposure for the hours shown in Table2 without giving evidence, to the unaided eye, of more than atotal of 8 isolated spots or pits. None shall be larger than 1 mmin diameter. Each individual test specimen shall not have morethan 5 isolated spots or pits, none larger than 1 mm in diameteron their r
24、espective surfaces. Spots within 10 mm of the edgesof the panels are not counted.7.4 Test Specimens and SamplingsUnless otherwisespecified, the sampling plans of Test Method B 602 or theequivalent ISO 4519 shall be used to test the coatings.7.4.1 Test specimens shall be of the same alloy and surface
25、condition as the articles represented. Test specimens shall be150 by 100 mm.8. Keywords8.1 conversion coating; non-hexavalent chromium conver-sion coating; non-rinsed; rinsedASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mention
26、edin 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
27、 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 consideration at a meeting of
28、 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 Harbor Drive, PO Box
29、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).TABLE 1
30、 Classification of Non-hexavalent ChromiumConversation CoatingsClass Corrosion Protection1 Maximum corrosion resistance generally used as a final finish2 Moderate corrosion resistance, used as a paint base and forbonding to rubber3 Decorative, slight corrosion resistance, low electrical contactresis
31、tance4 Moderate corrosion resistance, used as a paint base and forbonding to rubberTABLE 2 Relative Corrosion ResistanceExposure Time, hACoatingClassNon-Heat-TreatableWrought AlloysHeat-Treatable Alloysand Cast Alloys witha Nominal SiliconContent 1 %1 500 336 482 250 168 243 168 120 124 500 336 48AThe exposure times are indicative of the relative corrosion resistance of thevarious coating classes on the different alloys, but no direct relationship existsbetween performance in the neutral salt spray test and performance in service.B921022
