Process Development and Characterization of Anisotropic NdFeB Permanent Magnets Produced with a Modified Powder Extrusion Moulding Method

This dissertation investigates and develops the powder extrusion moulding (PEM) process as a novel approach to produce anisotropic NdFeB magnets, with a particular focus on the use of powders obtained from end-of-life (Eol) magnets through hydrogen processing of magnetic scrap (HPMS). This work aimed to develop a scalable prodcution approach that enables the production of anisotropic NdFeB permanent magnets using the PEM process. A comprehensive series of experiments was conducted to optimize extrusion conditions, magnetic particle alignment, and the parameters for debinding and sintering. The research was structured into two phases. In the first phase, the feasibility of producing isotropic NdFeB magnets using the PEM process was demonstrated. The focus was on identifying a suitable combination of machine configuration, feedstock formulation, and processing parameters that ensured high dimensional stability of the extruded strands while preventing oxidation of the sensitive powder. In the second phase, the process was extended to anisotropic magnets by implementing magnetic particle alignment in situ during extrusion. Finite element simulations were used to design suitable alignment tool geometries, and extrusion trials confirmed a high degree of alignment with Br/Js ratios of up to 0.95. The extrusion process was further optimized so that a degree of alignment of 0.96 could be achieved by adjusting the extrusion temperature. In addition, the debinding and sintering strategies were refined so that sintered magnets with a carbon content of only 0.045 wt.% could be produced, while oxygen uptake from the powder to the sintered part typically increased by 0.4 wt.% depending on the processing conditions. The results demonstrate that PEM with in situ alignment enables the scalable production of anisotropic NdFeB permanent magnets with high magnetic performance. Compared to conventional powder metallurgy, PEM provides near-net-shape capability, eliminates costly post-processing, and allows for a continuous and industrially scalable manufacturing route. This dissertation therefore contributes to the advancement of sustainable recycling and manufacturing technologies for rare-earth magnets.