Production of sintered NdFeB magnets from scrap alloy powders

Rare earth metals are at highest supply risk of all metals for clean technologies due to supply restrictions. Rare earth elements are essential for the highest energy permanent magnets which are used in high-tech green applications such as wind turbines and electric motors. This rare earth 'crisis' has been addressed by many authors by reducing or substituting the rare earths for less critical elements. The focus of this thesis, however, is on recycling of rare earth magnetic materials. Previous work has been focused on recycling NdFeB by re-sintering and blending alloying elements to improve the final magnetic properties. However, none of these studies have addressed the systematic addition of alloying elements or the particle size effect on the final magnetic performance of the recycled magnet. The work in this thesis is aimed at maximising the magnetic performance of recycled NdFeB magnets by investigating the effect of the manufacturing route and the influence of adding alloying elements. Uncoated end-of-life sintered NdFeB were exposed to hydrogen at room temperature to break them down into a friable powder; which was then milled, sieved, aligned, pressed and sintered into recycled magnets. The resulting magnets were tested on a permeameter at room temperature, 75 and 150oc to measure the magnetic properties. Scanning electron microscopy was used to assess the microstructures. Mechanical properties such as Vickers hardness and fracture toughness were also studied