Weight loss test of sintered NdFeB magnets (HAST, PCT)
Sintered NdFeB permanent magnets are magnetic materials with the highest magnetic properties discovered so far, and are widely used in wind power generation, new energy vehicles, maglev trains, intelligent robots and other fields. The sintered NdFeB magnet adopts powder metallurgy process, and the raw material contains highly active rare earth elements, which makes its corrosion resistance in high temperature and high humidity environment worse, which greatly limits its use in various complex working conditions. Therefore, higher requirements are put forward for the comprehensive performance of NdFeB magnets in practical applications.
In 2019, my country has compiled the national standard "Sintered NdFeB Weight Loss Test Method", which is currently in the stage of submission and has not yet been implemented. Today, I will introduce the sintered NdFeB weight loss test (also known as high temperature, high pressure and high humidity accelerated aging test) in combination with the review draft of this test plan.
The weight loss test is used to test the corrosion resistance of the NdFeB substrate, and the sample is a magnet substrate without any protective layer. When the test sample is exposed to the high temperature and high pressure water vapor environment, the weight loss refers to the mass loss per unit surface area of the magnet orientation surface due to corrosion, the unit is mg/cm2.
Hast test and PCT test
Weightlessness test can be carried out in Hast mode and PCT mode. Many people do not know the difference between Hast test and PCT test. Let us first introduce the difference between these two tests.
1. The test conditions are different:
PCT is the English abbreviation of pressure cooker test, which refers to the high-pressure accelerated aging life test. It is a saturated type, the default humidity is 100%, and the temperature, humidity and pressure rise or fall at the same time. It is used to test the sealing performance and aging performance of magnetic material products.
Hast is a non-saturated type, temperature, humidity (70%~100%), pressure can be adjusted according to needs, can do high temperature and high humidity, high and low temperature cycle, double 95, high temperature, high humidity and high pressure test, also known as aging test
2. Different test equipment
Both PCT test and Hast test have special testing equipment and cannot be mixed.
3. In addition to testing the corrosion resistance of the magnet base material, the PCT test can also test the corrosion resistance of NdFeB finished products (products after processing and surface coating treatment), within a certain time (12h, 24h, 72h, etc.) Whether it can ensure that the surface of the sample does not corrode is the evaluation index.