Effect of the first hot extrusion temperature on microstructure and magnetic properties of second-extrusion Nd₂Fe₁₄B/α- Fe nanocomposite

Two hot extrusions were used to fabricate bulk dense permanent magnets of Nd₂Fe₁₄B/α-Fe nanocomposite. Effect of the first-extrusion temperature on the microstructure and magnetic properties of second-extrusion magnets was investigated. The second-extrusion magnets featured fine-grained microstructure and good surface quality. The first-extrusion temperature had important effect on the density, microstructure and magnetic properties of second-extrusion magnets. The density and grain size of second-extrusion magnets decrease with the increase of the first-extrusion temperature. When the first-extrusion temperature was 950 °C, the best magnetic properties, including remanence of 1.02 T, coercivity of 308.5 kA/m and maximum energy product of 94.4 kJ/m³, were achieved in the second-extrusion magnets. The refined microstructure and increased density led to the best magnetic properties of the second-extrusion magnets obtained at the first-extrusion of 950 °C as compared to the second-extrusion magnets achieved at other first-extrusion temperatures such as 1000 °C, 1050 °C and 1100 °C.