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Effects of Initial Alloy on Microstructure and Magnetic Properties During Hot Deformation of Nd–Fe–B HDDR Powder

The effect of an initial alloy on microstructure and magnetic properties of Nd–Fe–B hydrogenation–disproportionation–desorption–recombination (HDDR) magnets during hot-deformation process have been studied with strip-casting alloy of composition Nd12.5FebalCo0.3Nb0.2B6.4 which have different microstructures. HDDR powders were produced by HDDR process with strip-casting alloy after pre-annealing or no pre-annealing. Obtained HDDR powders were subjected to hot-pressing at 700 °C under 400 MPa in vacuum and subsequently to die-upsetting at 800 °C with deformation conditions such as strain rate of 0.01 s−1 and height reduction of 77%. The microstructure of the initial alloys showed a large difference depending on the presence or absence of pre-annealing. The coercivity of HDDR powders using alloy after pre-annealing and no pre-annealing was different about 2 kOe. In addition, the remanence of hot-deformed magnet using HDDR powder produced with no pre-annealing alloy was higher than that with pre-annealing alloy although the hot deformation was conducted under the same condition and the remanence of two kinds of starting HDDR powder was almost the same. It was confirmed that the microstructure and magnetic properties of hot-deformed magnet depend on the microstructure of the initial alloy.