1、Designation: B 840 99 (Reapproved 2004)Standard Specification forElectrodeposited Coatings of Zinc Cobalt Alloy Deposits1This standard is issued under the fixed designation B 840; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、 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 for electrode-posited zinc cobalt alloy coatings on metals.1.2 Th
3、e following precautionary caveat pertains to the testmethod portion only, Section 8, of this specification: Thisstandard does not purport to address all of the safety concerns,if any, associated with its use. It is the responsibility of the userof this standard to establish appropriate safety and he
4、althpractices and determine the applicability of regulatory limita-tions prior to use.2. Referenced Documents2.1 ASTM Standards:2B117 Practice for Operating Salt Spray (Fog) ApparatusB 183 Practice for Preparation of Low-Carbon Steel forElectroplatingB 242 Guide for Preparation of High-Carbon Steel
5、ForElectroplatingB 320 Practice for Preparation of Iron Castings for Electro-platingB 322 Guide for Cleaning Metals Prior to ElectroplatingB 374 Terminology Relating to ElectroplatingB 487 Test Method for Measurement of Metal and OxideCoating Thickness by Microscopical Examination of aCross SectionB
6、 499 Test Method for Measurement of Coating Thick-nesses By the Magnetic Method: Nonmagnetic Coatingson Magnetic Basis MetalsB 504 Test Method for Measurement of Thickness of Me-tallic Coatings by the Coulometric MethodB 507 Practice for Design ofArticles to Be Electroplated onRacksB 568 Test Method
7、 for Measurement of Coating Thicknessby X-Ray SpectrometryB 571 Practice for Qualitative Adhesion Testing of MetallicCoatingsB 602 Test Method for Attribute Sampling of Metallic andInorganic CoatingsB 697 Guide for Selection of Sampling Plans for Inspectionof Electrodeposited Metallic and Inorganic
8、CoatingsB 762 Test Method of Variables Sampling of Metallic andInorganic CoatingsB 849 Specification for Pre-Treatments of Iron or Steel forReducing Risk of Hydrogen EmbrittlementB 850 Guide for Post-Coating Treatments of Steel for Re-ducing the Risk of Hydrogen EmbrittlementD 3951 Practice for Comm
9、ercial Packaging3. Terminology3.1 DefinitionsMany terms used in this specification aredefined in Terminology B 374.3.2 Definitions of Terms Specific to This Standard:3.2.1 significant surface, nthat portion of a coated arti-cles surface where the coating is required to meet all therequirements of th
10、e coating specification for that article.Significant surfaces are usually those that are essential to theserviceability or function of the article or can be a source ofcorrosion products or tarnish films that interfere with thefunction or desirable appearance of the article. Significantsurfaces are
11、those surfaces that are identified by the purchaserby, for example, indicating them on an engineering drawing ofthe product or marking a sample item of the product.4. Classification4.1 There is one coating class, and it is defined as Class1deposits having 99 mass % zinc, the balance being cobalt.4.2
12、 There are five coating types and they are defined asfollows:4.2.1 Type aWith colorless (blue bright) chromate con-version coatings.4.2.2 Type bWith yellow chromate conversion coating.4.2.3 Type cWith bronze chromate conversion coating.4.2.4 Type dWith black chromate conversion coating.4.2.5 Type eA
13、ny of the above types plus organic topcoat.1This specification is under the jurisdiction of ASTM Committee B08 onMetallic and Inorganic Coatings and is the direct responsibility of SubcommitteeB08.08.04 on Soft Metals.Current edition approved Aug. 1, 2004. Published August 2004. Originallyapproved i
14、n 1993. Last previous edition approved in 1999 as B 840 99.2For 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.1C
15、opyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.NOTE 1Whereas colored chromate conversion coatings are usuallymeant to include various shades of yellow to bronze when used withnon-alloyed zinc, yellow and bronze chromate conversion coa
16、tings areconsidered distinctly different when applied to alloyed zinc coatings andare formulated specifically to produce the desired coating.4.3 There are three grades according to thickness and aredefined as follows:Minimum Thickness, m New ASTM Grade Old ASTM Grade66112 12 218 18 35. Ordering Info
17、rmation5.1 In order to make the application of this specificationcomplete, the purchaser needs to supply the following infor-mation to the seller in the purchase order and drawings.5.1.1 Title, ASTM designation number, and date of issue ofthis specification.5.1.2 Deposit by classification including
18、class, type, andgrade (see 4.1, 4.2, 4.3).5.1.3 Composition and metallurgical condition of the sub-strate to be coated.5.1.4 Location of significant surfaces (3.2.1).5.1.5 Heat treatment for stress relief, whether it has beenperformed by purchaser or is required (6.7).5.1.6 Heat treatment after elec
19、troplating, if required (6.8).5.1.7 Whether or not location of rack marks is to be defined(6.3.1).5.1.8 Any requirement for special test specimens (8.1.1).5.1.9 Acceptance inspection procedure to be used (Section7).5.1.10 Any requirement for certification (Section 10).5.1.11 Any other items needing
20、agreement. For the purposesof this specification, prior agreement on the nature of the finishis required as items plated in bulk may differ in appearancefrom those that are rack plated.6. Coating Requirements6.1 SubstrateThe metal to be plated shall be free of flawsand defects that will be detriment
21、al to the zinc alloy coating. Itshall be subjected to such cleaning, pickling, and electroplatingprocedures as are necessary to yield deposits with the desiredquality.NOTE 2Proper preparatory procedures and thorough cleaning areessential to ensure satisfactory adhesion and corrosion resistance perfo
22、r-mance of the coating. Materials used for cleaning should not damage thebasis metal, for example, by causing defects such as pits, intergranularattack, or stress corrosion cracking. It is recommended that the followingASTM practices for cleaning, where appropriate, be used: PracticesB 183, B 320, a
23、nd B 322 and Guide B 242.6.1.1 The electroplating shall be applied after all basis metalheat treatments have been completed.6.2 Nature of Coating:6.2.1 The coating shall consist of a zinc cobalt alloy that isapproximately 99 mass % zinc and the balance cobalt.6.2.2 The coating shall be produced from
24、 an aqueouselectroplating system, either alkaline or acid, and may bespecified at the discretion of the purchaser.6.2.3 The coating shall have such supplementary conversioncoatings as defined in 4.2 and specified in the purchase order.6.3 Appearance:6.3.1 The coating on all readily visible surfaces
25、shall havean acceptable and characteristic appearance as agreed upon bythe purchaser and seller. The coating shall be uniform insofaras the basis metal will permit. When the article is to be platedon a rack, contact marks may be unavoidable. Location of suchmark(s) shall be indicated on the article
26、or its drawing.6.3.2 Defects and variations in appearance that arise fromsurface conditions of the substrate (scratches, pores, roll marks,inclusions, and the like) and that persist in the coating despitethe observance of good metal finishing practices, shall not because for rejection. The coating s
27、hall be adherent, free fromblisters, pits, or discontinuities, and shall be free of cracks inthe as plated state. Flaking shall be cause for rejection in eitherthe as plated state or after subsequent operations.NOTE 3These coatings are commonly used in automotive applica-tions where subsequent formi
28、ng, bending, and crimping operations arecommonly performed. These operations will necessarily detract from theperformance of the coatings. While some cracking of coatings will beunavoidable, flaking of the coatings after these subsequent operationsshall be cause for rejection.NOTE 4Coatings generall
29、y perform better in service when the sub-strate over which they are applied is smooth and free of torn metal,inclusions, pores, and other defects. The specifications covering theunfinished product should provide limits for these defects.Ametal finishercan often remove defects through special treatme
30、nts, such as grinding,polishing, abrasive blasting, chemical etches, and electropolishing. How-ever, these are not normal in the treatment steps preceding the applicationof the coating. When they are desired, they are the subject of specialagreement between the purchaser and the seller.6.4 Thickness
31、The thickness of the coating everywhere onthe significant surfaces as defined in 3.2.1 and shall conform tothe requirements of the specified grade as defined in 4.3.NOTE 5The thickness of electrodeposited coatings varies from pointto point on the surfaces of a product (see Practice B 507). The thick
32、nessis less in interior corners and in holes. Such surfaces are often exemptfrom thickness requirements. If the full thickness is required in thoselocations, the electroplater will have to use special techniques that willprobably raise the cost of the process.NOTE 6The coating requirement of this sp
33、ecification is a minimum.Variation in the thickness from point to point on an article and from articleto article in a production lot is inherent in electroplating. Therefore, if allof the articles in a production lot are to meet the thickness requirement, theaverage coating thickness for the product
34、ion lot as a whole will be greaterthan the specified minimum.6.5 AdhesionThe coating shall withstand normal handlingand storage conditions without chipping, flaking, or othercoating damage and shall conform to the minimum require-ments set forth in Section 8.6.6 Corrosion ResistanceThe corrosion res
35、istance of thecoating may be evaluated using the method in Appendix X1.6.7 Pretreatment of Iron and Steel for Reducing the Risk ofHydrogen Embrittlement:6.7.1 Parts that are made of steels with ultimate tensilestrengths of 1000 MPa (hardness of 31 HRC or greater), thathave been machined, ground, col
36、d formed, or cold straightenedsubsequent to heat treatment shall require stress relief heattreatment when specified by the purchaser, the tensile strengthto be supplied by the purchaser. Specification B 849 may beconsulted for a list of pretreatments that are widely used.B 840 99 (2004)26.8 Post-Coa
37、ting Treatments of Iron and Steel for Reducingthe Risk of Hydrogen Embrittlement:6.8.1 Parts that are made of steels with ultimate tensilestrengths of 1000 MPa (hardness of 31 HRC or greater), aswell as surface hardened parts, may require post-coatinghydrogen embrittlement relief baking when specifi
38、ed by thepurchaser, the tensile strength to be supplied by the purchaser.Guide B 850 may be consulted for a list of post-treatments thatare widely used.7. Sampling7.1 The sampling plan used for the inspection of a quantityof the coated articles shall be as agreed upon between thepurchaser and the se
39、ller.NOTE 7Usually when a collection of coated articles, the inspection lot(7.2), is examined for compliance with the requirements placed on thearticles, a relatively small number of the articles, the sample, is selected atrandom and is inspected. The inspection lot is then classified as complyingor
40、 not complying with the requirements based on the results of theinspection of the sample. The size of the sample and the criteria ofcompliance are determined by the application of statistics. The procedureis known as sampling inspection. Three standards, Test Method B 602,Guide B 697, and Test Metho
41、d B 762 contain sampling plans that aredesigned for the sampling inspection of coatings. Test Method B 602contains four sampling plans, three for use with tests that are nondestruc-tive and one when they are destructive. The buyer and seller may agree onthe plan or plans to be used. If they do not,
42、Test Method B 602 identifiesthe plan to be used. Guide B 697 provides a large number of plans and alsogives guidance in the selection of a plan. When Guide B 697 is specified,the buyer and seller need to agree on the plan to be used. Test MethodB 762 can be used only for coating requirements that ha
43、ve a numericallimit, such as a coating thickness. The test must yield a numerical valueand certain statistical requirements must be met. Test Method B 762contains several plans and also gives instructions for calculating plans tomeet special needs. The buyer and the seller may agree on the plan orpl
44、ans to be used. If they do not, Test Method B 762 identifies the plan tobe used.NOTE 8When both destructive and nondestructive tests exist for themeasurement of a characteristic, the purchaser needs to state which is tobe used so that the proper sampling plan is selected.Atest may destroy thecoating
45、 but in a noncritical area; or, although it may destroy the coating,a tested part can be reclaimed by stripping and recoating. The purchaserneeds to state whether the test is to be considered destructive ornondestructive.7.2 An inspection lot shall be defined as a collection ofcoated articles that a
46、re of the same kind, have been produced tothe same specification, have been coated by a single supplier atone time or at approximately the same time under essentiallyidentical conditions, and are submitted for acceptance orrejection as a group.7.3 If special test specimens are used to represent the
47、coatedarticles in a test, the number used shall be that required in 8.1.1.8. Test Methods8.1 Special Test Specimens:8.1.1 The permission or the requirement to use special testspecimens, the number to be used, the material from whichthey are to be made, and their shape and size shall be stated bythe
48、purchaser.NOTE 9Test specimens often are used to represent the coated articlesin a test if the articles are of a size, shape, or material that is not suitablefor the test or if it is preferred not to submit articles to a destructive testbecause, for example, the articles are expensive or few in numb
49、er. Thespecimen should duplicate the characteristics of the article that influencesthe property being tested.8.1.2 Special test specimens used to represent articles in anadhesion, porosity, corrosion resistance, or appearance testshall be made of the same material, shall be in the samemetallurgical condition, and shall have the same surfacecondition as the articles they represent. They shall be placed inthe production lot of and be processed along with the articlesthey represent.8.1.3 Special test specimens used to represent articles in acoating thickness test
