GB/T 34491-2017Coatings for sintered neodymium iron boron permanent magnets (English PDF)

3.1 Substrate

The substrate referred to in this Document refers to the workpiece that requires surface treatment.

3.2 Electroplating

In order to obtain properties or dimensions that the substrate does not have, a metal or alloy layer with good bonding strength is deposited on the substrate by electrolysis.

3.3 Barrel electroplating

An electroplating process in which bulk workpieces are electrodeposited in a rotating, oscillating or otherwise moving container.

3.4 Vat plating (GB) or still plating (US)

Electroplating in which the parts to be plated are independently connected to the rack.

3.5 Electroless plating or actocalytic plating

6.1 Appearance quality

6.1.1 The coating surface shall be free of rust spots, yellow marks, water stains and other bad marks. The passivation film on the coating surface shall be complete and there shall not be adhered whitening. On the main surface of the workpiece, there shall be no obvious coating defects, such as blistering, pores, corner burrs, coating cracks or local coating absence and coating shedding, etc., which are visible to the naked eye.

6.1.2 During vat plating, 2 to 4 visible and unavoidable conductive contact marks of the hanger are allowed on the non-main surface; but this contact mark shall not expose the substrate and does not affect the overall protective performance of the product.

6.2 Thickness

The coating in the center area of the outer surface of the sintered NdFeB sample is relatively uniform. Under typical use environment conditions, the typical thickness range of various coatings in this area is shown in Table 4. The coating thickness is the guarantee of providing sufficient corrosion resistance. As the severity of the use environment increases, the coating thickness shall also increase accordingly.

The coating appearance inspection of the coated product shall be carried out in accordance with the provisions of QB/T 3814.

7.2 Thickness

The coating thickness is usually measured in accordance with the provisions of GB/T 16921.

When the coating thickness exceeds the detection range, it shall be carried out in accordance with the provisions of GB/T 4955. In case of dispute, the provisions of GB/T 6462 may be adopted. For the measurement of the coating thickness, it is usually recommended to select 3 to 5 points within the phi 5 mm area of the center of the largest plane of the outer surface of the sample, and then take the average value as the measurement result. The maximum allowable deviation of the total coating thickness measurement is ±2 µm or the measured value × 15%, whichever is greater.

7.3 Corrosion resistance test

7.3.1 Neutral salt spray test

The neutral salt spray test of the coating is carried out in accordance with the provisions of GB/T 2423.17. The continuous spray test method is adopted. The test conditions are. 35°C ± 2°C, 5%±1% NaCl solution (mass fraction), and the pH of the collected salt spray precipitation solution is between 6.5 and 7.2. The specimen placement angle affects the test results. The inclination angle of the specimen surface in the salt spray chamber is 45°±5°.

7.3.2 Damp heat test

The test shall be performed in accordance with the provisions of GB/T 2423.50. The test conditions are. temperature 85 °C ±2 °C, relative humidity 85%±5%.

7.3.3 Low temperature test

The test shall be performed in accordance with the provisions of GB/T 2423.1.

7.3.4 High pressure accelerated aging test

Put the specimen into a high pressure accelerated aging test device containing distilled water or deionized water with a resistivity greater than 1.0 M ohm·cm. The test conditions for the unsaturated mode are. temperature 120 °C ±2 °C, air pressure 0.2 MPa, and relative humidity controlled within the range of 1000 -5%; the test conditions for the more stringent saturated mode are. temperature 120 °C ±2 °C, air pressure 0.2 MPa, and relative humidity 100%.

7.4 Adhering strength test

7.4.1 Tensile test method

The test shall be performed in accordance with the provisions of GB/T 5210. The tensile test method can quantitatively give the adhering strength value between the coating and the substrate, which must be greater than the value agreed upon by the supplier and the purchaser.

7.4.2 Cross-cut method

The test shall be performed in accordance with the provisions of GB/T 5270.

7.4.3 Thermal shock test method

The adhering strength of nickel coating, nickel-copper-nickel coating and composite coating with them as the bottom layer shall be tested according to the thermal shock test method specified in GB/T 5270, heating to 250 °C, keeping warm for 1 h, and cooling in water no higher than 25 °C.

7.4.4 High and low temperature impact test method

The test shall be performed according to the temperature change test Na specified in GB/T 2423.22-2012.

7.4.5 Drop test method

The test shall be performed according to the provisions of GB/T 2423.8.

8.1 Inspection and acceptance

8.1.1 The coating products shall be inspected by the supplier's quality inspection department to ensure that the products meet the requirements of this Standard.

8.1.2 The purchaser shall inspect the received products according to the provisions of this Standard. If the inspection results are inconsistent with the provisions of this Standard, they shall be raised within 1 month from the date of receipt of the product and resolved through negotiation between the supplier and the purchaser. If arbitration is required, the supplier shall jointly take samples and entrust an inspection agency recognized by both parties to conduct inspections.

8.2 Batching

Each batch of coated products shall be composed of the same production process and the same specifications.

8.3 Inspection items

Each batch of coated products shall be subject to type inspection items such as appearance quality, coating thickness, corrosion resistance and adhering strength.

8.4 Sampling

be unqualified.

9.1 Marking

The coated products that pass the inspection shall have labels with the following contents.

a) Supplier name and address;

b) Stamp from the supplier's quality inspection department;

c) Supplier's inspection date.

9.2 Packaging

Coated products shall be packaged with clean soft materials and properly stored. The packaging material shall not affect the performance of the coating.

9.3 Transportation and storage

Coated products shall be handled with care during transportation; stored in a dry environment away from corrosion; the storage environment shall also be moisture-proof, away from heat sources, strong magnetic fields, and avoid direct sunlight exposure.

9.4 Quality certificate

Each batch of coated products shall be accompanied by a quality certificate, indicating.

a) Supplier name;

b) Coated product name;

c) Batch number, number of pieces;

d) Results of various analysis and inspections and stamp from quality inspection department;

e) This standard number;

f) Inspection date; g) Exit-factory date. […]