Corrosion of rapidly solidified neodymium-iron-boron (NdFeB) permanent magnets and protection via sacrificial zinc coatings

Rapidly solidified NdFeB alloys were found to corrode actively at open circuit in aerated Na2SO4 and NaCl at 30 °C and 80 °C. Estimated penetration rates (greater than 27 mil year−1) indicate the need for corrosion control methods. e of sacrificial zinc coatings in controlling the corrosion of NdFeB alloys may have previously been overlooked because of two potential limitations: incomplete protection and hydrogen damage. The electrochemical activity of Nd may prevent zinc from providing complete sacrificial protection to NdFeB at breaks in the coating, and cracking could occur when hydrogen production is galvanically stimulated on NdFeB at breaks in the coating. tudy focuses on the evaluation of the protection conferred to NdFeB when a Zn/NdFeB galvanic couple is formed due to coating penetration. Quantitative solution analysis was used to demonstrate that the dissolution of Nd, Fe and B is essentially prevented by the galvanic coupling of NdFeB to zinc in NaCl at 25 °C. Galvanic coupling to zinc also reduces the rate of environmentally assisted cracking of NdFeB. Sacrificial zinc coatings appear to be a viable, cost-effective corrosion control method for NdFeB, and the limitations described above should not preclude their use in this application.