As the third generation of rare earth permanent magnet materials, sintered Nd-Fe-B has excellent comprehensive magnetic properties and high cost performance. It is widely used in various fields. It is an important basic functional material for scientific and technological progress and social development. However, with the continuous development of wind power generation, new energy vehicles and other emerging industries, higher requirements are put forward for the stability of sintered NdFeB magnets in service. The mass loss per unit of magnetic orientation surface area caused by corrosion of sintered NdFeB permanent magnet substrate samples exposed to high temperature and high pressure steam was tested by the hast high temperature, high pressure and high humidity test method.

In this test, the corrosion resistance and corrosion resistance of the samples were tested by the hast-450 high pressure accelerated aging test chamber produced by riukai Ruikai instrument. The equipment can simulate the high temperature, high pressure and high humidity environment, which is used to accelerate the corrosion of samples and reduce the test cycle of R & D products. Generally, the saturation mode is used for corrosion resistance test. The temperature in the saturation mode is 120 ℃, the humidity is 100% relative humidity, and the pressure is 2atm.

It can be used to test the corrosion resistance of magnets (i.e. weight loss) and the corrosion resistance of magnets coated with protective coating / coating (i.e. PCT). For the weight loss test of the magnet, the test sample can be taken out every certain time, the corrosion products on the sample surface can be removed and weighed, and the corresponding mass loss per unit surface of the sample can be calculated, that is, weight loss.

For the PCT test, observe the corrosion of the test sample every certain time. The judgment basis is that the first visible corrosion product appears on the surface of the test sample, and the test can be terminated. At this time, the corresponding test time is the PCT resistance test time of the sample.

test method

The high pressure accelerated aging test chamber (hast-450) is used to test the corrosion weight loss of the samples under high temperature, high pressure and high humidity. The test conditions are 100% relative humidity, 120 ℃ and 2 ATM.

Test procedure

Before the test, the test chamber and sample frame shall be cleaned with test water conforming to the above water requirements of this standard.

Conduct visual appearance inspection, dimension measurement and weighing of samples before test according to relevant requirements; The surface condition shall be photographed and recorded when required by the customer; If necessary, draw the sample placement diagram in the sample box to ensure one-to-one correspondence before and after the test.

Put the sample frame containing the sample into the hast test box, and the distance between the sample and the inner wall of the box shall not be less than 50 mm. The heating time for reaching the test conditions shall not exceed 2 hours, and the timing shall be started after reaching the test conditions.

If the test is temporarily interrupted due to power failure or supplement of humidified water during the test, it is not allowed to open the test chamber; The cumulative interruption time shall not exceed 3 hours (including temperature drop and temperature rise recovery time), and shall be described in the test report. If the interruption time is longer than 3 hours, re sampling shall be conducted for test in principle.

After the specified test time, the accumulated cooling and storage time of samples in the test chamber shall be less than 2 hours.

When taking out samples from the test chamber, avoid scalding by hot steam; The samples taken shall be kept at room temperature for 0.5 hours before visual inspection, photography and removal of corrosive substances. The whole process of visual inspection, photography, removal of corrosive substances, drying and mass weighing shall be completed within 5 hours after the termination of the test.

In the weight loss test, once there is a corrosion pit on the surface of sintered NdFeB permanent magnet sample, with the expansion of corrosion, after reaching a certain critical point, the corrosion weight loss caused by grain spalling on the surface of the sample increases almost linearly with the increase of test time. The critical point of weight loss is about 5mg/cm2.