Effects of grain boundary ternary alloy doping on corrosion resistance of (Ce,Pr,Nd)-Fe-B permanent magnets

Abstract To satisfy the application of different environments, grain boundary doping is commonly used in the preparation of sintered magnets to improve the coercivity and the corrosion resistance. In this paper, the alloys were prepared by mixing different ratios of the master alloy (Ce,Pr,Nd)-Fe-B and the sintering aid (Pr,Nd)-Al. The coercivity of sintered (Ce,Pr,Nd)-Fe-B magnet is substantially enhanced by doping 2 wt% of (Pr,Nd)-Al, while the maximum energy product decreases slightly. We systematically investigated the corrosion behavior and microstructure of the sintered magnets in order to determine the mechanism of the degradation. The sintered (Ce,Pr,Nd)-Fe-B magnets with 2 wt% of (Pr,Nd)-Al addition exhibit the decreasing corrosion rate compared with others, due to the distribution of intergranular phases. The electrode potential difference between the main phase and the RE-rich phase is reduced by the addition of Al, improving the potential and stability of RE-rich phase due to the higher electrode potential of Al than that of Nd, Pr or Ce. In addition, the element distribution of the magnets doped by (Pr,Nd)-Al indicates that the Al-rich shell formed at the marginal area of the Ce-rich phase improves its stability. Therefore, intergranular adding ternary (Pr,Nd)-Al alloy powders results in both high coercivity and good corrosion resistance synchronously.