ASTM B695

ASTM Protective Coatings

ISO PROTECTIVE COATINGS

ASTM B695 Mechanical Zinc Plated Fasteners

Stud Bolts, Nuts, Screws, Threaded Rod & Washers

ASTM B695 Classification

ASTM B695 specification covers the requirements for a coating of zinc mechanically deposited on iron and steel basis metals.The coating is provided in several thicknesses up to and including 107 µm. The seven thickest classes are usually referred to as “mechanically galvanized.
ASTM F959 DTI washers zinc coated by the mechanical deposition process in accordance with the requirements of Class 55 of Specification ASTM B695, or the DTIs shall be zinc coated by the thermal diffusion process in accordance with the requirements of Class 25 of Specification A1059.

Classes

Zinc coatings are classified on the basis of thickness, as follows:

Class	Minimum Thickness, µm
110	107
80	81
70	69
65	66
55	53
50	50
40	40
25	25
12	12
8	8
5	5

ASTM B695 Types

Zinc coatings are identified by types on the basis of supplementary treatment required, as follows

Type I-As coated, without supplementary treatment.
Type II-With colored chromate conversion treatment.

ASTM B695 Requirements

Appearance: The coating as deposited shall have a uniform silvery appearance, and a matte to medium – bright luster.

Process

Stress Relief Treatment: All steel parts that have an ultimate tensile strength of 1000 MPa and above and that contain tensile stresses caused by machining, grinding, straightening, or cold – forming operation shall be given a stress – relief heat treatment prior to cleaning and metal deposition. The temperature and time at temperature shall be 190 6 15°C for a minimum of 3 h so that maximum stress relief is obtained without reducing the hardness below the speciﬁed minimum.

High Strength steels

Strength steels (which become embrittled when charged with hydrogen) and that have heavy oxide or scale shall be cleaned before application of the coating in accordance with Practice B242. In general, nonelectrolytic alkaline, anodic – alkaline, and some inhibited acid cleaners are preferred to avoid the risk of producing hydrogen embrittlement from the cleaning procedure.
For low – carbon steels, see Practice B183. Useful guidelines are also given in Guide B322.
Mechanical deposition of zinc coatings shall consist, in general, of all of the steps listed below, and in the sequence as shown:
Preparation of the surface of the parts to be coated, by chemical (generally acidic) procedure to an extent that permits uniformly satisfactory results from subsequent steps.
Deposition of a thin metal coating, generally of copper, by immersion in appropriate chemical solutions, without the use of electric current. There are no thickness requirements for this coating.

Tumbling of the parts that have been treated according to and in a container with the following:

The zinc metal to be deposited, in powder form;
Impact media, which includes glass, for example, or other substances that are essentially inert to the chemicals of the deposition process. The function of this media is to aid in providing mechanical forces to drive the metal powder onto the substrate parts;
A “promoter” or “accelerator” which aids in the uniform deposition of the metal powder; and
A liquid medium, generally water.

Separation of the parts from the solid and liquid media.

Rinsing.
Drying.

Supplementary Treatments

Colored Chromate Conversion Treatments (Type II): Colored chromate conversion treatment for Type II shall be done in a solution containing hexavalent chromium ions. This solution shall produce a bright or semibright continuous, smooth, protective ﬁlm with a uniform color that is capable of ranging from yellow through bronze and olivedrab to brown and black and that are capable of being dyed to a desired color. Bright dips that do not contain salts that yield ﬁlms containing hexavalent chromium ions are precluded as treatments for producing Type II coatings.
Waxes, lacquers, or other organic coatings are not prohibited from being used to improve lubricity, and the need for them shall be supplied in the purchase order or other governing document. Supplemental lubrication treatments shall not be used to ensure conformance to the salt spray corrosion resistance requirements
Lubrication of grade DH nuts processed in accordance with this speciﬁcation and used with Speciﬁcation A325 high-strength bolts is a requirement of Speciﬁcation A325 and paragraph 4.8 of Speciﬁcation A563.
Surface Defects: Defects and variations in appearance in the coating that arise from surface conditions of the substrate (scratches, pores, roll marks, inclusions, etc.) and that persist in the ﬁnish despite the observance of good metal ﬁnishing practices shall not be cause for rejection.
When signiﬁcant surfaces are involved on which the speciﬁed thickness of deposit cannot readily be controlled, it is incumbent upon the purchaser and manufacturer to recognize the necessity for either thicker or thinner deposits.
For example, to reduce buildup in thread roots, holes, deep recesses, bases of angles, and similar areas, the deposit thickness on the more accessible surfaces will have to be reduced proportionately.
Adhesion: The zinc coating shall be sufficiently adherent to the basis metal to pass the tests.

Class Type	White Corrosion
Class:	55-110	50	40	25	12	8	5
I	A	A	A	A	A	A	A
II	72	72	72	72	72	72	72
Class Type	Red Rust
I	no requirement	300	250	192	96	56	36
II	no requirement	300	250	192	96	72	72

Corrosion Resistance: The presence of corrosion products visible to the unaided eye at normal reading distance at the end of the speciﬁed test periods stated in Table 1 shall constitute failure, except that corrosion products at edges of specimens shall not constitute failure. Slight “whisps” of white corrosion, as opposed to obvious accumulations, shall be acceptable.
On parts with Type II coatings, the greater number of hours for either white corrosion products or rust shall apply. For example, for Type II, Class 8, the test shall be continued until the 72 – h requirement is met for white corrosion products; similarly, for Type II, Class 25, if no white corrosion products appear before 72 h, test shall be continued until the 192 – h requirement for basis metal corrosion is met.
Absence of Hydrogen Embrittlement: Springs and other high-strength parts subject to ﬂexure shall be held for a minimum of 48 h at room temperature after coating before being loaded, ﬂexed, or used. Such high strength steel parts shall be free of hydrogen embrittlement. When speciﬁed in the purchase order, freedom from embrittlement shall be determined by the test speciﬁed herein

ASTM B695 Test Methods

Test Specimens: If needed, use test specimens to represent the coated articles in a test if the articles are of a size, shape, or material that is not suitable for the test, or if it is preferred not to submit articles to a destructive test because, for example, the articles are expensive or few. The permission or the requirement to use test specimens, their number, the material from which they shall be made, and their shape and size shall be stated in the purchase order or other governing document.
The test specimen shall duplicate those characteristics of the article that inﬂuence the property being tested, and it shall be processed with the article through those process steps that inﬂuence the property.
The test specimen used to represent an article in an adhesion, corrosion resistance, or appearance test shall be made of the same material, shall be in the same metallurgical condition, and shall have the same surface condition as the article it represents, and it shall be placed in the production lot of, and be processed along with, the article it represents.
A test specimen used to represent an article in a coating thickness test shall be introduced into the process at the point where the coating or coatings are applied and it shall be carried through all steps that have a bearing on the coating thickness.
When a test specimen is used to represent a coated article in a thickness test, the specimen will not necessarily have the same thickness and thickness distribution as the article unless the specimen and the article are of the same general size and shape. Therefore, before accepting coated articles on the basis of a thickness test performed on representative test specimens, the relationship between the thickness on the specimen and the thickness on the part shall be established. The criterion of acceptance shall be that thickness on the specimen that corresponds to the required thickness on the article.
Workmanship: Quality of workmanship shall be determined by the unaided eye at normal reading distance.
Thickness: The thickness of the coating shall be determined by the microscopical method (Test Method B487) or the magnetic method (Test Method B499), as applicable. Other methods are not prohibited, provided that they demonstrate a measurement uncertainty less than 10 %.
The thickness of the coating shall be measured at the location or locations for both signiﬁcant and nonsigniﬁcant surfaces of the product where the coating is expected to be the thinnest or at such locations as speciﬁed on the purchase order.
Thickness measurements of Type II deposits shall be made after application of the supplementary treatment. The Type II chromate conversion coatings shall be removed from the test area before the thickness is measured. Removal shall be done by using a very mild abrasive (such as a paste of levigated alumina or magnesium oxide) rubbed on gently with the ﬁnger.
Adhesion: Adhesion of the zinc deposit to the basis metal shall be tested in a manner that is consistent with the service requirements of the coated article. The ability to separate the coating from the substrate by peeling, as distinct from ﬂaking caused by rupture of the deposit or of the basis metal, shall be evidence of failure. One of the following methods for determining adhesion shall be used:
The part shall be plastically deformed, if possible, to rupture as speciﬁed on the purchase order
The surface of the coated article shall be scraped or sheared with a sharp edge, knife, or razor blade through the coating down to the basis metal and examined under 4× magniﬁcation.
Salt Spray Corrosion Resistance: The 5 % neutral salt spray (fog) test as deﬁned in Practice B117 shall be used.
If samples with Type II coatings are to be examined both for white corrosion products and for rust, use separate samples to determine the end point for white corrosion and for rust. This is to permit uninterrupted exposure for the longer of the two test periods required without having to wash specimens for examination, in accordance with Practice B117.
Parts with Type II supplementary chromate ﬁlm shall be aged at room temperature for 24 h before subjection to the salt spray test.
Parts with coatings of wax, etc., shall not be used as samples for corrosion testing for conformance to the requirements of 6.5.
Absence of Hydrogen Embrittlement: Coated parts to be tested for the absence of embrittlement from cleaning shall be tested for brittle failure in accordance with a suitable method to be speciﬁed on the purchase order. The description of the method shall include the means of applying a load to the part, the stress or load level to be applied, the duration of the test, the waiting time that must elapse between deposition of the zinc and testing or use of the part, and the criterion of failure.
Parts that must conform to U.S. Government requirements shall be subjected to such loading conditions described above for 200 h minimum.

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