Hot extrusion process for Nd-Fe-B magnets

Abstract

Hot extrusion, hot rolling, and die upsetting processes have been developed for fabricating Nd-Fe-B permanent magnets. Unlike the conventional sintering process, these processes result in the formation of a [100] texture and a preferred direction of magnetization. The primary advantage of the hot deformation processes over the sintering process is the elimination of the ingot crushing, milling, pressing with the magnetic field, sintering, and heat treating steps which results in a more economic and simpler process. An added advantage is good corrosion resistance of the magnet. Among these hot deformation processes, hot extrusion has various advantages over the other hot deformation processes such as availability of more varied shapes of the magnet; for example, a radially oriented (ring) magnet can be fabricated only by this process. Because of these advantages, the extruded magnets are suitable for applications in motors and generators, acoustic devices, computer peripherals, beam focusing devices, medical devices, and magnetic resonance imaging (MRI), etc. This paper describes the effect of extrusion ratio and temperature, heat treatment, morphology, and particle size of the starting material, grain size, and chemical composition on the resulting magnetic properties. Temperature stability of the extruded magnet will also be discussed.