Surface Flatness
High-quality neodymium-iron-boron magnets should have a smooth and flat surface. This is because neodymium-iron-boron magnets are manufactured through the powder metallurgy process. During the forming and processing, if the process is well controlled, there will be no obvious bumps or dents on the surface. For example, high-precision mold pressing can make the magnet surface achieve a high level of flatness. If there are obvious pits or protrusions on the surface, it may indicate problems in the manufacturing process, such as uneven powder pressing or insufficient processing precision.
Color Uniformity
Under normal circumstances, the color of neodymium-iron-boron magnets should be uniformly distributed. Different surface treatment methods will make the magnets present different colors. For example, they will be shiny silver after nickel plating and white after zinc plating. Regardless of the color, it should be evenly distributed on the same surface. If the color is not uniform, there may be problems with the electroplating or coating process, such as uneven concentration of the electroplating solution or inconsistent coating thickness during coating, which may affect the anti-corrosion performance and overall quality of the magnets.
Dimensional Accuracy
Accurate dimensions are crucial for the quality of neodymium-iron-boron magnets. High-quality magnets will be processed strictly in accordance with the designed dimensions during the production process. When measured with tools like calipers, the error between the actual dimension and the nominal dimension should be within a reasonable range. For example, for some small and precise neodymium-iron-boron magnets, the tolerance of length, width, and thickness may be controlled within ±0.05 mm. Dimensional accuracy not only affects the installation and use of the magnets but also has a certain impact on their magnetic field distribution.
Remanence (Br)
Remanence refers to the magnetic induction intensity retained by a magnetic material after it is magnetized to a saturated state and the external magnetic field disappears. It is a key indicator for measuring the magnetic strength of neodymium-iron-boron magnets. Generally, it is measured by professional Gauss meters. High-quality neodymium-iron-boron magnets have relatively high remanence. For example, for N35 model neodymium-iron-boron magnets, their remanence is usually between 1.18 - 1.22 T (tesla). The higher the remanence, the stronger the magnetic field intensity that the magnet can provide, and it performs better in applications with high requirements for magnetic field intensity, such as motors and speakers.
Coercivity (Hc)
Coercivity refers to the reverse magnetic field intensity required to reduce the magnetic induction intensity of a magnetic material to zero. It reflects the magnet's ability to resist demagnetization. For neodymium-iron-boron magnets, the higher the coercivity, the stronger their anti-demagnetization performance. In complex environments such as high temperature and reverse magnetic fields, magnets with high coercivity can better maintain their magnetism. For example, in some motors that need to work at relatively high temperatures, neodymium-iron-boron magnets with high coercivity are required to prevent the magnetic properties from weakening due to the increase in temperature.
Maximum Energy Product (BH)max
The maximum energy product is a comprehensive indicator for measuring the performance of neodymium-iron-boron magnets. It represents the maximum value of the magnetic field energy generated by the magnet in the air gap. The higher the maximum energy product, the more magnetic field energy the magnet can provide under the same volume. For common high-performance neodymium-iron-boron magnets, their maximum energy product can reach 40 - 50 MGOe (megagauss-oersted) or even higher. Magnets with a high maximum energy product are crucial in magnetic field applications that require high energy density, such as magnetic levitation systems.
Hardness
Neodymium-iron-boron magnets need to have a certain hardness to ensure that they will not be easily deformed during use. Their hardness can be measured by hardness testing equipment. Appropriate hardness enables them to maintain the stability of shape and performance when subjected to certain external impacts or friction. For example, in some magnetic connectors that need to be frequently inserted and removed, neodymium-iron-boron magnets with qualified hardness can better withstand the mechanical stress during the insertion and removal process.
Toughness
Toughness reflects the ability of neodymium-iron-boron magnets to absorb energy before fracture. Although neodymium-iron-boron magnets are relatively brittle themselves, a certain degree of toughness can prevent them from breaking when subjected to small external forces. In practical applications, for example, in some equipment that may be subject to vibration or slight collisions, magnets with good toughness can better adapt to the environment and reduce the risk of damage.
Salt Spray Test
The salt spray test is a common method for evaluating the corrosion resistance of neodymium-iron-boron magnets. Place the magnets in a salt spray test chamber to simulate the marine environment or harsh environments with high humidity and high salt content. After a certain period of time (such as 24 hours, 48 hours, etc.) of the salt spray test, observe whether there are rust spots, corrosion pits, or other phenomena on the surface of the magnets. High-quality neodymium-iron-boron magnets should have no obvious signs of corrosion on the surface after the specified time of the salt spray test, which indicates that their electroplating or other anti-corrosion measures are effective.
Damp Heat Test
The damp heat test is used to simulate the corrosion resistance of magnets in high-temperature and high-humidity environments. Place the magnets under certain temperature (such as 40 °C - 60 °C) and humidity (such as 90% - 95% RH) conditions for a period of time (such as 72 hours). If there is no obvious change in the performance and appearance of the magnets after the test, it indicates that their damp heat resistance is good and they can be used normally in similar harsh environments.
