Purchase order shall specify not less than the following:
- Lot hydrogen embrittlement testing if required (see 4.4.2) and sampling
- Basis metal to be plated
- Tensile strength or hardness of the basis metal
- Pre-plate stress relief to be performed by plating processor (time and temperature)
- Special features, geometry or processing present on parts that requires special attention by the plating processor
- Hydrogen embrittlement relief to be performed by plating processor (parameters or reference document)
- Quantity of pieces to be plated.
I – As plated
II – With supplementary chromate treatment
III – With supplementary phosphate treatment
1 – 0.0005 inch, minimum
2 – 0.0003 inch, minimum
3 – 0.0002 inch, minimum
Unless otherwise specified, parts having an ultimate tensile strength greater than 200 ksi (HRC 43) shall not be plated in accordance with this spec.
Steel parts which have been machined, ground, cold-formed, or cold-straightened after heat treatment, shall be stress relieved in accordance with Table 1 or Table 1A, as applicable. Stress relief shall precede shot peening, cleaning, and plating for relief of damaging residual tensile stresses. Stress relief is not required for fasteners if all cold working is limited to cold working of the head-to-shank fillet and thread rolling after heat treatment.
Hydrogen Embrittlement Relief Treatment
All parts shall be baked within 4 hours after the plating operation is completed as specified in Table 1 or Table 1A, as applicable. Plated springs and other parts subject to flexure shall not be flexed prior to hydrogen embrittlement relief treatment. In the case of Types II and III treated parts which require baking, the baking treatment shall be done prior to the application of the supplementary coatings. Cadmium plated surfaces passivated as a result of the baking operation shall be reactivated prior to receiving the Type II supplementary chromate treatment. The following alloys are not considered susceptible to hydrogen embrittlement from the cadmium plating process, and therefore do not require the hydrogen embrittlement relief treatment (see Tables 1 and 1A), or the hydrogen embrittlement relief test:
- UNS S66286, UNS N07718, UNS R30159, UNS R30035, UNS N04400, UNS N06600, UNS N07750
- 300 series austenitic stainless steels
- Aluminum, and aluminum alloys.
The plating shall be applied after all basis metal heat treatments and mechanical operations, such as machining, brazing, welding, forming and perforating of the article, have been completed.
Cadmium shall be deposited on the basis metal without a preliminary plating of other metal, except in the case of parts made of corrosion resistant alloys on which a preliminary plating of nickel or copper may be necessary, or on parts made of aluminum on which a preliminary treatment, such as the zincate process or preliminary plating of copper or electroless nickel, may be necessary.
Statement on Luster/Brightener Options:
When determining luster/brightener usage/capabilities, there are multiple factors to consider; along with strict requirements depending on part characteristics. Please contact AOTCO where we will take the time to work through these parameters and determine how they pertain to your specific part(s).
Type II – not subsequently completely coated. Chromate treatment. Colors: Bronze, brown, olive drab, yellow, and forest green. Objectives are to prevent white corrosion spots and prevent finger marking.
Should NOT be used if parts will be continuously exposed to 149F or higher, or intermittently exposed to 300F or higher.
Type III – subsequently completely coated. Phosphate treatment. Produces tightly adherent film conforming to Type I of TT-C-490.
Primary objective is to form a coating base. Phosphate finish is preferred for parts that will subsequently be completely coated.
5.7 Packaging Limitations
Cadmium plated articles should not be packed in non-ventilated containers, either together or in contact with electrical equipment, because of the danger of deleterious effect on cadmium plating from unstable organic electrical insulation. In addition to organic electrical insulation, phenolic resinous substances and others containing unsaturated carbon-to-carbon linkages, such as oil, paint and impregnated paper, etc., cause an abnormal attack on cadmium by setting free, in the presence of moisture, formic acid, butyric acid, etc. Corrosion of cadmium coatings and steel basis metal has been noted when cadmium plated articles have been packaged in direct contact with container materials such as wood or cardboard. Corrosion has been especially severe if the container materials have become wet or have been stored under conditions of high humidity.