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ASTM (F1136 / F1136M)
Standard Specification for
Chromium/Zinc Corrosion Protective Coatings for Fasteners
1. Scope
1.1 This specification covers the basic requirement for there grades of chromium/zinc inorganic
coatings for threaded fasteners.
1.2 These coatings are applied by conventional dip-spin or dip-drain methods.
1.3 The coating process does not induce hydrogen embrittement providing that the fasteners
have not been pretreated with an acid.
2. Reference Documents
2-1 A S T M Standards :
B117 >Test Methods for Salt Spray(Fog)Testing
D1000 >Test Methods for Pressure-Sensitive Adhesive Coating Tapes Used for Electrical and
Electronic Applications
D2247 >Practice for Testing Water Resistance of Coatings in 100% Relative Humidity
E122 >Practice for Choice of Sample Size to Estimate a Measure of Quality for Lot or Process.
3. Classification
3.1 These coatings are classified into three grades according to the requirements in Table 1.

Table 1 Classification of coatings
GradeNo. Chromium/Zinc
Coating Weight,(g/㎡)
Thickness, ㎛
Salt Spray, h
14. 0 - 17. 2
20. 4 - 23. 6
20. 4 - 27. 0
Clear sealer
5. 0 - 6. 0
6. 0 - 13. 0
7. 0 - 13. 0
1 4 4
2 4 0
4 0 0
4. Ordering Information
4.1 Orders for material under this specification shall include the following information :
4.1.1 Quantity of parts.
4.1.2 Grade of coating.
4.1.3 Any additions to the specification as agreed upon by the purchaser and the supplier.
5. Requirements
5.1 Appearance -The coating shall have a uniform appearance free from tears and other
discontinuities which may affect the appearance or performance, or both, of the coating.
5.2 Adhesion -The coating shall no evidence of blistering or other changes in appearance after
exposure to humidity testing for a minimum of 96 h. In addition there shall be no more than
3.0 mm peel-back from the intersection of scribed lines that are taped tested immediately
following a 10 min recovery period from the humidity test and there shall be no other peeling
under tape(see6.3 and 6.4).
5.3 Corrosion - There coatings shall be capable of withstanding neutral salt spray testing for the
minimum h specified in Table 1. Unless otherwise defined, acceptable corrosion resistance
shall be where there is no base metal corrosion on significant surfaces.
5.3.1 Significant surfaces are defined as the exposed surfaces of the fastener when it is installed
ina normal manner. Surfaces on which a controlled deposit ordinarily cannot be obtained,
sushas holes, recesses, bases of angles,and similar areas are normally exempt from
therequirements of significant surfaces.
5.4 Blister -There shall be no signs of blisters after testing in accordance with 6.1 and 6.3
5.5 Thread Fit - The coating shall not have an adverse affect on normal installation and removal
practices as determined by the proper GO thread gauge. Excessive coating on the threaded
surface may be acceptable only when the fastener passed the torque test outlined in 7.2.3.
5.5.1 The thickness> of the coating is limited by the basic thread size. Where greater thickness is
necessary the internal threads may be produced oversized (before coating) providing the
finished product (after coating) meets all the specified mechanical properties. Where
mechanical properties are not specified, over sizing is subject to the approval of the
6.Test Methods
6.1 Corrosion - Corrosion resistance shall be tested in accordance with Test Method B 117
6.2 Coating Thickness> - The coating thickness may be determined by the microscopic
examinationof a cross section taken perpendicular to the significant surface or by the

Note -The weigh-strip-weigh method involves weighing the test specimen before and after the
coating is stripped. The method requires a reagent that dose not attack the base metal.
Coating weight must be within the ranges given in Table 1. >6.3 Humidity Test >- The humidity test shall be conducted in accordance with Practice D 2247
(100% relative humidity at 100 F (38 ℃)).
6.4 Adhesion >- Semi-transparent pressure sensitive tape with an adhesive strength of 400 ± N/m
as tested in accordance with Test Methods D 1000 shall be used to test the adhesion of the
coating. The adhesive characteristic of the tape shall not change by more than 5 % of its
mean value within 12 months. The backing of the tape may consist of fiber-reinforced
cellulose acetate, unplasticized poly vinyl chloride, or polyester film. When performing the
adhesion test the tape shall be removed from the surface of the coated specimen with a
sharp jerk.
7.1 The purchaser may request samples in accordance with Practice E 122.
7.2 Referee Inspection - The following referee thread inspection may be utilized if the specified
go-gauge binds on the bolt,nut,or screw.
7.2.1Bolt or Screws - Assemble a phosphate test nut with a 2B or 6H class thread down the full
length of the thread.
7.2.2 Nut - Assemble a phosphate bolt or screw with a 2A or 6g class thread for a minimum of one
diameter through the nut.
7.2.3 The test nut,screw,or bolt must run freely for the total length without binding. If nonuniformity
of the coating causes difficulty in assembling the part,the coating may be found acceptable if
it requires no more than a torque equivalent to 0.06D N.m to assemble the part. 8. Rejection>
8.1 Materials that fail to conform to the requirements of this specification may be rejected.