ASTM_B_921_-_08_2013.pdf

Designation:B92108(Reapproved 2013)Standard Specification forNon-hexavalent Chromium Conversion Coatings onAluminum and Aluminum Alloys1This standard is issued under the fixed designation B921;the number immediately following the 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()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 conversioncoatings 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 protectivecoating 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 regulatory requirements prior to use.2.Referenced Documents2.1 ASTM Standards:2B117 Practice for Operating Salt Spray(Fog)ApparatusB602 Test Method for Attribute Sampling of Metallic andInorganic CoatingsD1730 PracticesforPreparationof AluminumandAluminum-Alloy Surfaces for PaintingD3359 Test Methods for Measuring Adhesion by Tape Test2.2 ISO Standards:ISO 2409 Paint and VarnishesCross-Cut Test3ISO 3768 Metallic CoatingsNeutral Salt Spray Test(NSSTest)3ISO 4519 Electrodeposited Metallic Coatings and RelatedFinishesSampling Procedures for Inspection by Attri-butes32.3 Federal Standard:Fed.Std.No.141 Paints,Varnish,Lacquer,and RelatedMaterials;Methods of Inspection42.4 Military Specification:MIL-DTL-5541 Chemical Conversion Coatings on Alumi-num and Aluminum Alloys4MIL-DTL-81706 Chemical Conversion Materials For Coat-ing Aluminum and Aluminum Alloys43.Terminology3.1 Definitions:3.1.1 non-rinsedconversion coatings that are dried imme-diately after the conversion coating step 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.NOTE1Non-rinsed conversion coatings are finding increased usageon fabricated parts and castings.3.1.2 rinsedconversion coatings that are rinsed in waterprior to drying.3.1.2.1 DiscussionThis type of coating is typically appliedto 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 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-DTL-5541).Class four conversion coatings only provide for paintedsalt fog corrosion resistance.4.2 The finishes are divided into four classes;their mostimportant characteristics are listed in Table 1.1This specification is under the jurisdiction of ASTM Committee B08 onMetallic and Inorganic Coatings and is the direct responsibility of SubcommitteeB08.07 on Conversion Coatings.Current edition approved May 1,2013.Published May 2013.Originallyapproved in 2002.Last previous edition approved in 2008 as B921 08.DOI:10.1520/B0921-08R13.2For 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.3Available from American National Standards Institute(ANSI),25 W.43rd St.,4th Floor,New York,NY 10036,http:/www.ansi.org.4Available from Standardization Documents Order Desk,DODSSP,Bldg.4,SectionD,700RobbinsAve.,Philadelphia,PA19111-5098,http:/dodssp.daps.dla.mil.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 5.Surfaces Preparation5.1 The surfaces of the parts to be conversion coated shallbe clean and free of any oxidation,scale,or soils such 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,becleaned 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 are 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 employe