GB/T 46763-2025Evaluation method for the grain boundary diffusion result of sintered rare earth iron boron permanent magnets (English PDF)

4.2 Measurement of magnetic properties of samples before grain boundary diffusion

4.2.1 The magnets before grain boundary diffusion treatment, after aging heat treatment, are processed into circular magnetic sheets with a diameter of 9 mm ~ 10 mm and a thickness of 2 mm ~ 10 mm, or rectangular magnetic sheets with a side length of 7 mm ~ 10 mm and a thickness of 2 mm ~ 10 mm.

4.2.2 Measure the intrinsic coercivity (HcJ1) and knee coercivity (Hk1) of the samples at room temperature according to the methods specified in GB/T 3217 or GB/T 29628.

4.3 Measurement of overall magnetic properties of samples after grain boundary diffusion

4.3.1 After grain boundary diffusion, the residual diffusion source material and oxides on the magnet sample surface are completely removed by grinding. The surface thickness removed by single-sided grinding is 50 µm ~ 100 µm.

4.3.2 After removing residual diffusion sources from the surface, if the sample size is too large to be directly tested for magnetic properties, the sample can be processed into a circular magnetic sheet with a diameter of 9 mm ~ 10 mm and a thickness of 2 mm ~ 10 mm, or a rectangular magnetic sheet with a side length of 7 mm ~ 10 mm and a thickness of 2 mm ~ 10 mm, without changing the sample's main diffusion direction (usually the easy magnetization direction).

4.3.3 Measure the intrinsic coercivity (HcJ2) and knee coercivity (Hk2) at room temperature of the sample according to the methods specified in GB/T 3217 or GB/T 29628.

4.3.4 The deviation between the temperature during measurement and the temperature at which the magnetic properties of the sample were measured before grain boundary diffusion shall not exceed 0.5 °C.

4.4 Measurement of internal magnetic properties of samples after grain boundary diffusion

4.4.1 After measuring the overall magnetic properties of the sample after grain boundary diffusion, symmetrically grind the main diffusion surfaces on both sides to the required final thickness. The thickness deviation between the two main diffusion surfaces shall be less than

0.1 mm. The sample thickness for measuring the internal magnetic properties of the grain boundary diffused magnet shall be

4.4.2 Measure the intrinsic coercivity (HcJ3) and knee coercivity (Hk3) at room temperature of the sample according to the methods specified in GB/T 3217 or GB/T 29628.

4.4.3 The deviation between the temperature during measurement and the temperature at which the magnetic properties of the sample were measured before grain boundary diffusion shall not exceed 0.5 °C.

4.5 Calculation of evaluation parameters of magnetic properties

4.5.1 Increase in intrinsic coercivity at room temperature of magnet after grain boundary diffusion The improvement in the overall magnetic properties of the magnet after grain boundary diffusion is expressed as the increase in intrinsic coercivity at room temperature (delta), calculated according to formula (1). where. HcJ2 - the intrinsic coercivity at room temperature of the magnet after grain boundary diffusion, in kilo-oerste (kOe); HcJ1 - the intrinsic coercivity at room temperature of the magnet after aging heat treatment and before grain boundary diffusion, in kilo-oerste (kOe).

4.5.2 Ratio of internal magnetic properties to overall magnetic properties of magnets after grain boundary diffusion The ratio of internal magnetic properties to overall magnetic properties of the magnet after grain boundary diffusion is expressed as the ratio of internal intrinsic coercivity (sigma) to overall intrinsic coercivity of the magnet and the ratio of internal knee coercivity

5.3.1 Reference samples

5.3.1.1 Use sintered rare earth iron boron permanent magnets with known single terbium (Dy) and dysprosium (Tb) contents as reference samples.

5.3.1.2 The mass fraction of single element Dy or Tb in the reference samples should preferably be one of the following values. 0, 0.5 %, 1 %, 2 %, 3 %, 5 %, 7 %, or 10 %.

5.3.1.3 The reference samples shall be circular or square sheets with a diameter or side length of 12 mm ~ 20 mm and a thickness of 5 mm ~ 10 mm.

5.3.1.4 The surface of the reference samples shall be uniform in color, clean, and flat, free from visible defects such as sand holes, cracks, and oxides, and shall be wrapped in rust-proof paper for preservation.