ASTM B840-99(2009)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:B840 −99(Reapproved 2009)
Standard Specification for
Electrodeposited Coatings of Zinc Cobalt Alloy Deposits
This standard is issued under the fixed designation B840; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope B571Practice for Qualitative Adhesion Testing of Metallic
Coatings
1.1 Thisspecificationcoverstherequirementsforelectrode-
B602Test Method for Attribute Sampling of Metallic and
posited zinc cobalt alloy coatings on metals.
Inorganic Coatings
1.2 The following precautionary caveat pertains to the test
B697Guide for Selection of Sampling Plans for Inspection
method portion only, Section 8, of this specification: This
of Electrodeposited Metallic and Inorganic Coatings
standard does not purport to address all of the safety concerns,
B762Test Method of Variables Sampling of Metallic and
if any, associated with its use. It is the responsibility of the user
Inorganic Coatings
of this standard to establish appropriate safety and health
B849Specification for Pre-Treatments of Iron or Steel for
practices and determine the applicability of regulatory limita-
Reducing Risk of Hydrogen Embrittlement
tions prior to use.
B850GuideforPost-CoatingTreatmentsofSteelforReduc-
ing the Risk of Hydrogen Embrittlement
2. Referenced Documents
D3951Practice for Commercial Packaging
2.1 ASTM Standards:
B117Practice for Operating Salt Spray (Fog) Apparatus
3. Terminology
B183Practice for Preparation of Low-Carbon Steel for
3.1 Definitions—Many terms used in this specification are
Electroplating
defined in Terminology B374.
B242Guide for Preparation of High-Carbon Steel for Elec-
3.2 Definitions of Terms Specific to This Standard:
troplating
3.2.1 significant surface, n—that portion of a coated arti-
B320Practice for Preparation of Iron Castings for Electro-
cle’s surface where the coating is required to meet all the
plating
requirements of the coating specification for that article.
B322Guide for Cleaning Metals Prior to Electroplating
Significant surfaces are usually those that are essential to the
B374Terminology Relating to Electroplating
serviceability or function of the article or can be a source of
B487Test Method for Measurement of Metal and Oxide
corrosion products or tarnish films that interfere with the
Coating Thickness by Microscopical Examination of
function or desirable appearance of the article. Significant
Cross Section
surfaces are those surfaces that are identified by the purchaser
B499Test Method for Measurement of CoatingThicknesses
by, for example, indicating them on an engineering drawing of
by the Magnetic Method: Nonmagnetic Coatings on
the product or marking a sample item of the product.
Magnetic Basis Metals
B504Test Method for Measurement of Thickness of Metal-
4. Classification
lic Coatings by the Coulometric Method
B507Practice for Design ofArticles to Be Electroplated on
4.1 There is one coating class, and it is defined as Class
Racks
1—deposits having 99 mass % zinc, the balance being cobalt.
B568Test Method for Measurement of Coating Thickness
4.2 There are five coating types and they are defined as
by X-Ray Spectrometry
follows:
4.2.1 Type a—With colorless (blue bright) chromate con-
This specification is under the jurisdiction of ASTM Committee B08 on version coatings.
Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee
4.2.2 Type b—With yellow chromate conversion coating.
B08.06 on Soft Metals.
4.2.3 Type c—With bronze chromate conversion coating.
Current edition approved Sept. 1, 2009. Published December 2009. Originally
4.2.4 Type d—With black chromate conversion coating.
approvedin1993.Lastpreviouseditionapprovedin2004asB840–99(2004).DOI:
10.1520/B0840-99R09.
4.2.5 Type e—Anyoftheabovetypesplusorganictopcoat.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
NOTE 1—Whereas colored chromate conversion coatings are usually
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on meant to include various shades of yellow to bronze when used with
the ASTM website. non-alloyed zinc, yellow and bronze chromate conversion coatings are
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B840−99 (2009)
considered distinctly different when applied to alloyed zinc coatings and
6.3.1 The coating on all readily visible surfaces shall have
are formulated specifically to produce the desired coating.
an acceptable and characteristic appearance as agreed upon by
4.3 There are three grades according to thickness and are the purchaser and seller. The coating shall be uniform insofar
defined as follows: as the basis metal will permit. When the article is to be plated
onarack,contactmarksmaybeunavoidable.Locationofsuch
Minimum Thickness, µm New ASTM Grade Old ASTM Grade
66 1
mark(s) shall be indicated on the article or its drawing.
12 12 2
6.3.2 Defects and variations in appearance that arise from
18 18 3
surfaceconditionsofthesubstrate(scratches,pores,rollmarks,
inclusions, and the like) and that persist in the coating despite
5. Ordering Information
the observance of good metal finishing practices, shall not be
5.1 In order to make the application of this specification
cause for rejection. The coating shall be adherent, free from
complete, the purchaser needs to supply the following infor-
blisters, pits, or discontinuities, and shall be free of cracks in
mation to the seller in the purchase order and drawings.
theasplatedstate.Flakingshallbecauseforrejectionineither
5.1.1 Title,ASTM designation number, and date of issue of
the as plated state or after subsequent operations.
this specification.
NOTE3—Thesecoatingsarecommonlyusedinautomotiveapplications
5.1.2 Deposit by classification including class, type, and
where subsequent forming, bending, and crimping operations are com-
grade (see 4.1, 4.2, 4.3).
monly performed. These operations will necessarily detract from the
5.1.3 Composition and metallurgical condition of the sub-
performance of the coatings. While some cracking of coatings will be
unavoidable, flaking of the coatings after these subsequent operations
strate to be coated.
shall be cause for rejection.
5.1.4 Location of significant surfaces (3.2.1).
NOTE 4—Coatings generally perform better in service when the
5.1.5 Heat treatment for stress relief, whether it has been
substrate over which they are applied is smooth and free of torn metal,
performed by purchaser or is required (6.7).
inclusions, pores, and other defects. The specifications covering the
5.1.6 Heat treatment after electroplating, if required (6.8).
unfinishedproductshouldprovidelimitsforthesedefects.Ametalfinisher
can often remove defects through special treatments, such as grinding,
5.1.7 Whether ornotlocationofrackmarksistobe defined
polishing, abrasive blasting, chemical etches, and electropolishing.
(6.3.1).
However, these are not normal in the treatment steps preceding the
5.1.8 Any requirement for special test specimens (8.1.1).
application of the coating. When they are desired, they are the subject of
5.1.9 Acceptance inspection procedure to be used (Section
special agreement between the purchaser and the seller.
7).
6.4 Thickness—The thickness of the coating everywhere on
5.1.10 Any requirement for certification (Section 10).
thesignificantsurfacesasdefinedin3.2.1andshallconformto
5.1.11 Anyotheritemsneedingagreement.Forthepurposes
the requirements of the specified grade as defined in 4.3.
ofthisspecification,prioragreementonthenatureofthefinish
NOTE 5—The thickness of electrodeposited coatings varies from point
is required as items plated in bulk may differ in appearance
to point on the surfaces of a product (see Practice B507).The thickness is
from those that are rack plated.
less in interior corners and in holes. Such surfaces are often exempt from
thickness requirements. If the full thickness is required in those locations,
the electroplater will have to use special techniques that will probably
6. Coating Requirements
raise the cost of the process.
6.1 Substrate—The metal to be plated shall be free of flaws
NOTE 6—The coating requirement of this specification is a minimum.
anddefectsthatwillbedetrimentaltothezincalloycoating.It
Variationinthethicknessfrompointtopointonanarticleandfromarticle
to article in a production lot is inherent in electroplating. Therefore, if all
shallbesubjectedtosuchcleaning,pickling,andelectroplating
ofthearticlesinaproductionlotaretomeetthethicknessrequirement,the
procedures as are necessary to yield deposits with the desired
averagecoatingthicknessfortheproductionlotasawholewillbegreater
quality.
than the specified minimum.
NOTE 2—Proper preparatory procedures and thorough cleaning are
6.5 Adhesion—Thecoatingshallwithstandnormalhandling
essential to ensure satisfactory adhesion and corrosion resistance perfor-
and storage conditions without chipping, flaking, or other
mance of the coating. Materials used for cleaning should not damage the
coating damage and shall conform to the minimum require-
basis metal, for example, by causing defects such as pits, intergranular
ments set forth in Section 8.
attack, or stress corrosion cracking. It is recommended that the following
ASTMpracticesforcleaning,whereappropriate,beused:PracticesB183,
6.6 Corrosion Resistance—The corrosion resistance of the
B320, and B322 and Guide B242.
coating may be evaluated using the method in Appendix X1.
6.1.1 Theelectroplatingshallbeappliedafterallbasismetal
6.7 Pretreatment of Iron and Steel for Reducing the Risk of
heat treatments have been completed.
Hydrogen Embrittlement:
6.2 Nature of Coating:
6.7.1 Parts that are made of steels with ultimate tensile
6.2.1 The coating shall consist of a zinc cobalt alloy that is
strengths of 1000 MPa (hardness of 31 HRC or greater), that
approximately 99 mass
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