1、Designation: B840 15Standard Specification forElectrodeposited Coatings of Zinc Cobalt Alloy Deposits1This standard is issued under the fixed designation B840; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisi
2、on. 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 for electrode-posited zinc cobalt alloy coatings on metals.1.2 The following precautio
3、nary 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 healthpractices and det
4、ermine the applicability of regulatory limita-tions prior to use.2. Referenced Documents2.1 ASTM Standards:2B117 Practice for Operating Salt Spray (Fog) ApparatusB183 Practice for Preparation of Low-Carbon Steel forElectroplatingB242 Guide for Preparation of High-Carbon Steel for Elec-troplatingB320
5、 Practice for Preparation of Iron Castings for Electro-platingB322 Guide for Cleaning Metals Prior to ElectroplatingB374 Terminology Relating to ElectroplatingB487 Test Method for Measurement of Metal and OxideCoating Thickness by Microscopical Examination ofCross SectionB499 Test Method for Measure
6、ment of Coating Thicknessesby the Magnetic Method: Nonmagnetic Coatings onMagnetic Basis MetalsB504 Test Method for Measurement of Thickness of Metal-lic Coatings by the Coulometric MethodB507 Practice for Design of Articles to Be Electroplated onRacksB568 Test Method for Measurement of Coating Thic
7、knessby X-Ray SpectrometryB571 Practice for Qualitative Adhesion Testing of MetallicCoatingsB602 Test Method for Attribute Sampling of Metallic andInorganic CoatingsB697 Guide for Selection of Sampling Plans for Inspectionof Electrodeposited Metallic and Inorganic CoatingsB762 Test Method of Variabl
8、es Sampling of Metallic andInorganic CoatingsB849 Specification for Pre-Treatments of Iron or Steel forReducing Risk of Hydrogen EmbrittlementB850 Guide for Post-Coating Treatments of Steel for Reduc-ing the Risk of Hydrogen EmbrittlementD3951 Practice for Commercial Packaging3. Terminology3.1 Defin
9、itionsMany terms used in this specification aredefined in Terminology B374.3.2 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 the coating specification for that article
10、.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 those surfaces that are identified by th
11、e 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 Class1a zinc cobalt alloy that is approximately 99% by mass zincand at minimum 0.5% by mass cobalt.4.2 The
12、re 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 EAny o
13、f the above types plus organic topcoat.NOTE 1Whereas colored chromate conversion coatings are usuallymeant to include various shades of yellow to bronze when used with1This specification is under the jurisdiction of ASTM Committee B08 onMetallic and Inorganic Coatingsand is the direct responsibility
14、 of SubcommitteeB08.06 on Soft Metals.Current edition approved May 1, 2015. Published May 2015. Originallyapproved in 1993. Last previous edition approved in 2009 as B840 99(2009). DOI:10.1520/B0840-15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Serv
15、ice at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1non-alloyed zinc, yellow and bronze chromate
16、conversion coatings 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.
17、 Ordering Information5.1 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 classificat
18、ion including 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 treatm
19、ent after electroplating, 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
20、items needing 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 wil
21、l be detrimental 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 re
22、sistance perfor-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: Practices
23、B183,B320, and B322 and Guide B242.6.1.1 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% by mass zinc and at minimum 0.5% bymass cobalt.6.2.2 The coating
24、 shall be produced from 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 re
25、adily visible surfaces 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 in
26、dicated on the article 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 r
27、ejection. The coating shall 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 applicationsw
28、here subsequent forming, bending, and crimping operations are com-monly 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.
29、NOTE 4Coatings generally perform better in service when thesubstrate 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 th
30、rough special treatments, such as grinding,polishing, abrasive blasting, chemical etches, and electropolishing.However, these are not normal in the treatment steps preceding theapplication of the coating. When they are desired, they are the subject ofspecial agreement between the purchaser and the s
31、eller.6.4 ThicknessThe 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 Practic
32、e B507). The thickness isless in interior corners and in holes. Such surfaces are often exempt fromthickness requirements. If the full thickness is required in those locations,the electroplater will have to use special techniques that will probablyraise the cost of the process.NOTE 6The coating requ
33、irement of this specification 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 thickne
34、ss for the production 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 Resistanc
35、eThe corrosion resistance 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 mac
36、hined, ground, cold 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 B849 may beconsulted for a list of pretreatments that are widely used.B840 1526.8
37、 Post-Coating 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 whe
38、n specified by thepurchaser, the tensile strength to be supplied by the purchaser.Guide B850 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 an
39、d the seller.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 com
40、plyingor 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 B602,Guide B697, and Test
41、 Method B762 contain sampling plans that aredesigned for the sampling inspection of coatings. Test Method B602contains 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 n
42、ot, Test Method B602 identifiesthe plan to be used. Guide B697 provides a large number of plans and alsogives guidance in the selection of a plan. When Guide B697 is specified,the buyer and seller need to agree on the plan to be used. Test MethodB762 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 B762contains several plans and also gives instructions for calculating plans tomeet special needs. The buyer and the seller may agree on the plan orpla
44、ns to be used. If they do not, Test Method B762 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 b
45、ut 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 are
46、 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 co
47、atedarticles 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 pu
48、rchaser.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 number
49、. 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 m
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