ASTM B766-86 pdf download.Standard Specification for Electrodeposited Coatings of Cadmium.
6. Materials and Manufacture
6.1 Nature ofCoating—The coating shall be essentially pure cadmium produced by electrodeposition usually from an alka- line cyanide solution.
6.2 High Tensile Strength Steel Parts—Steel parts having an ultimate tensile strength greater than 1650 MPa (approximately 50 HRC) shall not be plated by electrodeposition unless authorized by the purchaser.
6.3 Stress Relief—Steel parts having an ultimate tensile strength of 1050 MPa (approximately 35 HRC) and above, and that have been machined, ground, cold-formed, or cold- straightened shall be heat-treated at 190 6 15°C for 5 h or more for stress relief before cleaning and coating.
6.4 Preparatory Procedures—The basis metal shall be sub- jected to such cleaning procedures as necessary to ensure a surface satisfactory for subsequent electroplating. Materials used for cleaning shall have no damaging effects on the basis metal resulting in pits, intergranular attack, stress corrosion cracking, or hydrogen embrittlement. If necessary, cleaning materials for steel parts should be evaluated in accordance with Method F519. N OTE 4—For basis metal preparation, the following standards should be employed depending upon the metallurgical composition: Practices B183, B242, B253, B254, B281, B320, B322, B343, and B558. 6.5 Substrate—Cadmium shall be deposited directly on the basis metal part without an undercoat of another metal except when the part is either stainless steel or aluminum and its alloys. An undercoat of nickel is permissible on stainless steel.
With aluminum and aluminum alloys, the oxide layer shall be removed and replaced by a metallic zinc layer in accordance with Guide B253. For better adherence, a copper strike or a nickel coating may be applied to the zinc layer before electroplating with the cadmium.
6.6 Plating Process—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. 6.7 Hydrogen Embrittlement Relief—Steel parts having a tensile strength of 1200 MPa (approximately 38 HRC) and higher shall be baked at 190 6 15°C for 8 h or more within 4 h after electroplating to provide hydrogen embrittlement relief. Electroplated springs and other parts subject to flexure shall not be flexed, loaded, or used before the hydrogen embrittlement relief treatment. The baking treatment for hydrogen embrittle- ment relief shall be done before the application of any supplementary chromate treatment. When specified, freedom from embrittlement shall be determined. N OTE 5—For high-strength steels, greater than 1300 MPa or approxi- mately 40 HRC, it is strongly recommended that the baking time be extended to 23 h or more to ensure hydrogen embrittlement relief. N OTE 6—Electroplated steel parts, passivated by the baking operation for hydrogen embrittlement relief, require reactivation before the chro- mate treatment. This application, immersion in a dilute acid solution, should be done as soon as practical. If the chromating solution contains sulfuric acid, then the reactivating solution should be 1 part of sulfuric acid (sp gr 1.83) by volume added to 99 parts of water. If the chromating solution contains hydrochloric acid, then the reactivating solution should be 1 part of hydrochloric acid (sp gr 1.16) by volume added to 99 parts of water. Duration of immersion should be as brief as is consistent with the nature of the work. Separately racked items can be reactivated in approximately 5 s, whereas a perforated container of barrel-plated parts requires approximately 15 s.
6.8 Chromate Treatment:
6.8.1 Chromate treatments for Types II and III shall be done in or with special aqueous acidic solutions composed of hexavalent chromium along with certain anions that act as catalyst or film-forming compounds to produce a continuous smooth protective film. Chromic acid and nitric acid bright dips shall not be used for treatment to produce chromate coatings. When proprietary materials are used for this treatment, the instructions of the supplier should be followed.
6.8.2 The Type II film color shall range from an iridescent yellow or a thicker, more protective iridescent bronze or brown to the heavier olive drab. It may also be dyed to a desired color. When necessary, the color of the film shall be indicated by the purchaser and specified by the provision of a suitably colored sample or indicated on the drawing for the part.
6.8.3 The absence of color shall not be considered as evidence of lack of Type III film or as a basis for rejection. Presence of clear Type III film shall be determined by a spot test as specified in 10.4.
6.8.4 Waxes, lacquers, or other organic coatings shall not be used as a substitute for, nor may they be used in conjunction with, supplementary treatments when the purpose is to ensure conformance to the salt spray requirements. Waxes and the like, may be used to improve lubricity.ASTM B766 pdf download.