Study on the Corrosion Resistance of (Nd,Dy)–Fe–B Magnets Obtained by Grain Boundary Diffusion Method

Abstract

Nd-Fe-B sintered magnets were heat-treated in Dy vapor atmosphere for achieving (Nd,Dy)-Fe-B magnets by grain boundary diffusion (GBD). The magnetic properties, microstructure, and corrosion resistance of (Nd,Dy)-Fe-B magnets were systematically investigated. Results show that the intrinsic coercivity of magnets increases significantly after Dy diffusion. Dy atoms penetrate into the magnets through the grain boundaries, which not only increase the total amount of rare earth and widen the grain boundary but also form (Nd,Dy) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sub> B phase with higher anisotropic field on the grain surface layer. The intrinsic coercivity H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cj</sub> of (Nd,Dy)-Fe-B magnets increases from 16.86 to 21.60 kOe. When the testing time of highly accelerated aging tester is 96 h, the weight loss of pristine Nd-Fe-B magnets is 0.436 mg/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , while that of (Nd,Dy)-Fe-B magnets is 1.922 mg/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The results of weight loss test and potentiodynamic polarization curves show that the corrosion resistance of (Nd,Dy)-Fe-B magnets is worse than that of pristine magnets due to more rare earth amount and wider grain boundary.