JB/T 12855-2016Metallic coatings - Electroplated coatings of zinc-nickel alloys (English PDF)

3.1 White smog

Under the action of corrosive media, white oxides appear at the micro-cracks of the coating, causing a very slight change in the initial color of the coating.

3.2 White rust

Under the action of corrosive media, the passivation film and sealing film on the coating surface are destroyed, and the coating exhibits corrosion, producing powdery white corrosion products.

NOTE: The appearance of white rust is usually considered the first corrosion point.

3.3 Red rust

Under the action of corrosive media, the coating on the surface of the parts is destroyed, and the substrate shows the phenomenon of corrosion and the formation of red corrosion products in the form of spots.

NOTE: The formation of red rust is usually considered a secondary corrosion point.

4.1 Marking methods

According to GB/T 13911, the components of the coating marks are as follows.

Coating method Reference to this Standard - Substrate material/coating method · Coating layer name and thickness · Passivation film type and sealing The symbols, meanings, and passivation film colors of the marks are shown in Table 1 5 Information that the purchaser shall provide to the electroplating manufacturer

5.1 Required information

The purchaser shall provide the electroplating manufacturer with the following information.

a) Reference to this Standard;

b) The marks on the coating (see Chapter 4);

c) Indicating the main surfaces of the workpiece to be plated, such as by marking them with a drawing or providing a sample with appropriate marks;

d) The properties of the base metal, its surface condition, and the type of finishing (when these factors may affect the suitability and/or appearance of the plating);

e) Allowable plating defects on the workpiece (see 6.1.2);

f) Nickel content in electroplated coatings of zinc-nickel alloys;

g) Coefficient of friction of threaded fasteners;

h) The tensile strength of the workpiece and the heat treatment requirements before and/or after electroplating;

i) Sampling method, acceptance level, or other testing requirements.

5.2 Additional information

The purchaser shall provide the electroplating manufacturer with the following additional information.

a) Special requirements or limitations for the pretreatment of workpieces to be plated;

b) Special packaging requirements for plated workpieces;

c) Other requirements include areas for testing and rating of workpieces with special shapes.

6.1 Appearance

6.1.1 General requirements

The coating on the main surface of the workpiece is densely crystallized, uniform, smooth, and flat. The color of the passivation film shall be consistent across batches.

The typical colors of the passivation film for electroplated coatings of zinc-nickel alloys are shown in Table 1.

6.1.2 Allowable defects

Allowable defects in the coating include.

a) Slight water stains or uneven coloring.

b) Slight fixture marks are allowable on the coating of non-critical surfaces of the workpiece.

c) Differences in color and gloss of the same workpiece can be caused by differences in the workpiece's base material and surface condition.

d) Roughness and buildup may occur on the edges, corners, and edges of complex and large parts, but this shall not affect assembly quality or performance.

e) After hydrogen removal, the passivation film on the workpiece is slightly darker or uneven in color.

f) For blind holes (or slots, slits) with a diameter (or width) not greater than 10 mm, local areas of the surface where the depth is greater than the diameter (or width) are allowed to be uncoated; for through holes with a diameter not greater than 10 mm, local areas of the surface where the depth is greater than twice the diameter are allowed to be uncoated.

6.1.3 Unallowable defects

Unallowable defects in the coating include. […]