Abstract
Clean transportation and green energy are important components of Canada’s plan to achieve net-zero emissions by 2050, and so the applications of these technologies are on the rise. With that comes the growing demand for rare-earth (RE) containing permanent magnets which are widely implemented in electrification. The supply of RE elements (like Nd and Dy) is, however, at risk as they are produced by a limited number of countries. As such, recycling permanent magnets from end-of-life electrical products has become a critical alternative for countries that primarily rely on their import. This work presents a direct route for recycling of NdFeB permanent magnets into advanced powder suitable for metal Additive Manufacturing (AM).
The present recycling approach is distinct from other traditional routes like pyrometallurgy or hydrometallurgy as it involves direct recycling from end-of-life solid magnets to magnetic powder to new additively manufactured magnetic parts. The approach combines several conventional and novel processes namely (i) pulverizing the magnetic parts into particulates using hydrogen decrepitation, (ii) downsizing the particulates into fine powder, (iii) spheroidizing the powder using an induction plasma reactor, and (iv) additively manufacturing new parts using the spherical powder. The focus of this work is on the first three processes in order to optimize the operating conditions for enhanced physical and chemical properties of the recycled powder suitable for AM applications.
The process of hydrogen decrepitation is studied, with an emphasis on the physical and chemical reactions which occur in solid state leading to volume expansion of grain boundaries and consequently breakup of the end-of-life magnets. The effects of hydrogen decrepitation process parameters on maintaining the magnetic properties of powder is explained. Powder spheroidization process using the plasma reactor and its process optimization in accordance with the downstream manufacturing requirements are provided. The effect of plasma operating conditions on the particle size, morphology, density, flowability, and magnetic properties of powder has been discussed, and an optimum condition has been introduced.