ISSUE 011 Autumn 2021 Candela C-7 hydrofoil speedboat dossier l In conversation: Robert Hoevers l Battery recycling focus l Vehicle dynamics insight l ZeroAvia hydrogen-electric aircraft digest l Motor materials

E-motor developers share some best practice with Nick Flaherty about the design and materials that go into their products Driving forces T he need for low weight and high performance in e-mobility motors is driving a demand for specialist metal alloys and insulating materials that are also thermally conductive. There is a strong focus as well on how they are sourced, particularly with regard to heavy rare earth (HRE) elements. Dysprosium and neodymium for example are used to boost the magnetic field in permanent magnets, but they can be difficult to source and are expensive. Others, such as erbium, are more freely available, so magnet makers are looking at using those instead, as well as reducing the overall amount of HREs required. Motor makers are also looking at replacing the magnets entirely with new architectures and control algorithms that provide similar levels of efficiency to permanent magnet machines. Magnetic materials Neodymium magnets offer the highest energy density currently available commercially, and different neodymium-iron-boron alloys have different magnetic properties. The magnets are produced by sintering metallurgical powder and, depending on size, shape, tolerances, batch size and magnetic requirements, they are either cut from isostatically pressed blocks or die-pressed. This produces anisotropic magnets in all kinds of shapes for motors. The magnets are supplied with different coatings that deliver optimal protection and adhesive performance for virtually any application. These include nickel-copper-nickel, epoxy and even organic coatings. The latter was specifically developed by magnet and magnetic systems supplier JL Mag to give superior salt spray test resistance, with adhesion properties tailored for a specific application. Sintered samarium-cobalt magnets are used when stability is needed at temperatures of up to 250 C for SmCo 5 and up to 350 C for Sm 2 Co 17 . This is particularly important for motors for electric aircraft (see sidebar on page 60). But there are many other elements used in the magnets for electric motors of all kind, from small e-scooters up to large trucks and aircraft. “There’s aluminium, gallium, cobalt and 19 different elements – all of which have a small effect on the total performance,” says Jurre Stienen of The steels used in e-motors are chosen to provide the highest magnetic performance and strength for the lowest weight (Courtesy of Carpenter Technology) 56 Autumn 2021 | E-Mobility Engineering