Corrosion behavior of sintered Nd-Fe-B magnets

Abstract:

The corrosion behavior of Nd-Fe-B magnets was studied through immersion test in 3.5 wt.% NaCl solution. The morphology and composition of corrosion product were characterized by scanning electron microscope (SEM) and Raman spectroscopy. The corrosion behavior of the specimens were investigated by means of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The electrochemical equivalent circuits were used for fitting the EIS data. Results are as follows: Pitting corrosion, intergranularScorrosion and StotalScorrosion occurred in sequence during the immersion period. However, the corrosion product layer ofSlooseSstructure could only temporarily slow down the corrosion rate. At the initial stage, the Nd-rich phase atStheSgrain boundary preferentially dissolved into the media. Later the main phase particles were exposed to the corrosive solution and quicklyScorroded, causing a damage to the magnets. The corrosion products were mainly iron and neodymium oxides or hydroxides which was evolving with the immersion period.