Corrosion behavior of Sm2Co17 magnets under electrochemical hydrogen charging

• Hydrogen gas was generated on the surface of the magnet by electrochemical hydrogen charging, and the effect of hydrogen gas on the surface of Sm 2 Co 17 magnet at normal temperature and pressure was studied. • After the magnet absorbs hydrogen, the corrosion resistance decreases. The hydrogen enters the interior of the magnet along the surface defects, causing the surface to break. The absorption of hydrogen causes the main phase lattice of the magnet to become larger, and the magnet breaks. • The magnetic properties of the magnetized samples gradually decrease as the hydrogen charging time increases. Samarium–cobalt (SmCo)magnets have good high-temperature performance, but the corrosion behavior of SmCo magnets in hydrogen conditionshasnot been studied comprehensively. In this work, the corrosion behavior of Sm 2 Co 17 magnets in a hydrogen environment is assessed using electrolyzing hydrogen. Constant cathode current densities of 0, 6, 12, 25, 50, and 100 mA/cm 2 are used to charge the magnet surface with hydrogen in 1 mol/L KOH solution. Results show that as the hydrogen charging current ( i c ) increases, the amount of hydrogen absorbed by magnets increases gradually, and it reaches saturation when i c approaches the critical threshold of 50 mA/cm 2 . X-ray diffraction analysis of the physical phase indicates that hydrogen absorption causes lattice expansion of the main phase. With the increase in absorbed hydrogen content, the surface of the cobalt magnet loosens and peelsoff layer by layer.Consequently,itscorrosion resistance and magnetic properties gradually decrease.