ASTM B840-99
(Specification)Standard Specification for Electrodeposited Coatings for Zinc Cobalt Alloy Deposits
Standard Specification for Electrodeposited Coatings for Zinc Cobalt Alloy Deposits
SCOPE
1.1 This specification covers the requirements for electrodeposited zinc cobalt alloy coatings on metals.
1.2 The following precautionary caveat pertains to the test method portion only, Section 8, of this specification: This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: B 840 – 99
Standard Specification for
Electrodeposited Coatings of Zinc Cobalt Alloy Deposits
This standard is issued under the fixed designation B 840; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope B 697 Guide for Selection of Sampling Plans for Inspection
of Electrodeposited Metallic and Inorganic Coatings
1.1 This specification covers the requirements for electrode-
B 762 Method of Variables Sampling of Metallic and Inor-
posited zinc cobalt alloy coatings on metals.
ganic Coatings
1.2 The following precautionary caveat pertains to the test
B 849 Specification for Pretreatments of Iron or Steel for
method portion only, Section 8, of this specification: This
Reducing Risk of Hydrogen Embrittlement
standard does not purport to address all of the safety concerns,
B 850 Specification for Post-Coating Treatments of Iron or
if any, associated with its use. It is the responsibility of the user
Steel for Reducing Risk of Hydrogen Embrittlement
of this standard to establish appropriate safety and health
D 3951 Practice for Commercial Packaging
practices and determine the applicability of regulatory limita-
tions prior to use.
3. Terminology
2. Referenced Documents 3.1 Definitions—Many terms used in this specification are
defined in Terminology B 374.
2.1 ASTM Standards:
2 3.2 Definitions of Terms Specific to This Standard:
B 117 Practice for Operating Salt Spray (Fog) Apparatus
3.2.1 significant surface, n—that portion of a coated arti-
B 183 Practice for Preparation of Low-Carbon Steel for
3 cle’s surface where the coating is required to meet all the
Electroplating
requirements of the coating specification for that article.
B 242 Practice for Preparation of High-Carbon Steel for
3 Significant surfaces are usually those that are essential to the
Electroplating
serviceability or function of the article or can be a source of
B 320 Practice for Preparation of Iron Castings for Electro-
3 corrosion products or tarnish films that interfere with the
plating
function or desirable appearance of the article. Significant
B 322 Practice for Cleaning Metals Prior to Electroplating
surfaces are those surfaces that are identified by the purchaser
B 374 Terminology Relating to Electroplating
by, for example, indicating them on an engineering drawing of
B 487 Test Method for Measurement of Metal and Oxide
the product or marking a sample item of the product.
Coating Thickness by Microscopical Examination of a
Cross Section
4. Classification
B 499 Test Method for Measurement of Coating Thick-
4.1 There is one coating class, and it is defined as Class
nesses By the Magnetic Method: Nonmagnetic Coatings
1—deposits having 99 mass % zinc, the balance being cobalt.
on Magnetic Basis Metals
4.2 There are five coating types and they are defined as
B 504 Test Method for Measurement of Thickness of Me-
follows:
tallic Coatings by the Coulometric Method
4.2.1 Type a—With colorless (blue bright) chromate con-
B 507 Practice for Design of Articles to Be Electroplated on
3 version coatings.
Racks
4.2.2 Type b—With yellow chromate conversion coating.
B 568 Test Method for Measurement of Coating Thickness
3 4.2.3 Type c—With bronze chromate conversion coating.
by X-Ray Spectrometry
3 4.2.4 Type d—With black chromate conversion coating.
B 571 Test Methods for Adhesion of Metallic Coatings
4.2.5 Type e—Any of the above types plus organic topcoat.
B 602 Test Method for Attribute Sampling of Metallic and
Inorganic Coatings
NOTE 1—Whereas colored chromate conversion coatings are usually
meant to include various shades of yellow to bronze when used with
non-alloyed zinc, yellow and bronze chromate conversion coatings are
This specification is under the jurisdiction of ASTM Committee B-8 on
considered distinctly different when applied to alloyed zinc coatings and
Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee
are formulated specifically to produce the desired coating.
B08.08.04 on Light Metals.
Current edition approved Nov. 10, 1999. Published March 2000. Originally
published as B 840 – 93. Last previous edition B 840 – 94.
Annual Book of ASTM Standards, Vol 03.02.
3 4
Annual Book of ASTM Standards, Vol 02.05. Annual Book of ASTM Standards, Vol 15.09.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B 840
4.3 There are three grades according to thickness and are on a rack, contact marks may be unavoidable. Location of such
defined as follows: mark(s) shall be indicated on the article or its drawing.
6.3.2 Defects and variations in appearance that arise from
Minimum Thickness, μm New ASTM Grade Old ASTM Grade
66 1
surface conditions of the substrate (scratches, pores, roll marks,
12 12 2
inclusions, and the like) and that persist in the coating despite
18 18 3
the observance of good metal finishing practices, shall not be
5. Ordering Information
cause for rejection. The coating shall be adherent, free from
5.1 In order to make the application of this specification blisters, pits, or discontinuities, and shall be free of cracks in
the as plated state. Flaking shall be cause for rejection in either
complete, the purchaser needs to supply the following infor-
mation to the seller in the purchase order and drawings. the as plated state or after subsequent operations.
5.1.1 Title, ASTM designation number, and date of issue of
NOTE 3—These coatings are commonly used in automotive applica-
this specification.
tions where subsequent forming, bending, and crimping operations are
5.1.2 Deposit by classification including class, type, and
commonly performed. These operations will necessarily detract from the
grade (see 4.1, 4.2, 4.3). performance of the coatings. While some cracking of coatings will be
unavoidable, flaking of the coatings after these subsequent operations
5.1.3 Composition and metallurgical condition of the sub-
shall be cause for rejection.
strate to be coated.
NOTE 4—Coatings generally perform better in service when the sub-
5.1.4 Location of significant surfaces (3.2.1).
strate over which they are applied is smooth and free of torn metal,
5.1.5 Heat treatment for stress relief, whether it has been
inclusions, pores, and other defects. The specifications covering the
performed by purchaser or is required (6.7).
unfinished product should provide limits for these defects. A metal finisher
5.1.6 Heat treatment after electroplating, if required (6.8).
can often remove defects through special treatments, such as grinding,
5.1.7 Whether or not location of rack marks is to be defined
polishing, abrasive blasting, chemical etches, and electropolishing. How-
(6.3.1). ever, these are not normal in the treatment steps preceding the application
of the coating. When they are desired, they are the subject of special
5.1.8 Any requirement for special test specimens (8.1.1).
agreement between the purchaser and the seller.
5.1.9 Acceptance inspection procedure to be used (Section
7).
6.4 Thickness—The thickness of the coating everywhere on
5.1.10 Any requirement for certification (Section 10).
the significant surfaces as defined in 3.2.1 and shall conform to
5.1.11 Any other items needing agreement. For the purposes
the requirements of the specified grade as defined in 4.3.
of this specification, prior agreement on the nature of the finish
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 B 507). The thickness
from those that are rack plated.
is less in interior corners and in holes. Such surfaces are often exempt
from thickness requirements. If the full thickness is required in those
6. Coating Requirements
locations, the electroplater will have to use special techniques that will
6.1 Substrate—The metal to be plated shall be free of flaws
probably raise the cost of the process.
and defects that will be detrimental to the zinc alloy coating. It
NOTE 6—The coating requirement of this specification is a minimum.
shall be subjected to such cleaning, pickling, and electroplating Variation in the thickness from point to point on an article and from article
to article in a production lot is inherent in electroplating. Therefore, if all
procedures as are necessary to yield deposits with the desired
of the articles in a production lot are to meet the thickness requirement, the
quality.
average coating thickness for the production lot as a whole will be greater
NOTE 2—Proper preparatory procedures and thorough cleaning are than the specified minimum.
essential to ensure satisfactory adhesion and corrosion resistance perfor-
6.5 Adhesion—The coating shall withstand normal handling
mance of the coating. Materials used for cleaning should not damage the
and storage conditions without chipping, flaking, or other
basis metal, for example, by causing defects such as pits, intergranular
attack, or stress corrosion cracking. It is recommended that the following coating damage and shall conform to the minimum require-
ASTM practices for cleaning, where appropriate, be used: Practices
ments set forth in Section 8.
B 183, B 242, B 320 and B 322.
6.6 Corrosion Resistance—The corrosion resistance of the
coating may be evaluated using the method in Appendix X1.
6.1.1 The electroplating shall be applied after all basis metal
heat treatments have been completed. 6.7 Pretreatment of Iron and Steel for Reducing the Risk of
6.2 Nature of Coating: Hydrogen Embrittlement:
6.2.1 The coating shall consist of a zinc cobalt alloy that is 6.7.1 Parts that are made of steels with ultimate tensile
approximately 99 mass % zinc and the balance cobalt. strengths of 1000 MPa (hardness of 31 HRC or greater), that
6.2.2 The coating shall be produced from an aqueous have been machined, ground, cold formed, or cold straightened
electroplating system, either alkaline or acid, and may be subsequent to heat treatment shall req
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