Microstructure and Properties of Microwave-Sintered Nd2Fe14Bp/2024 Aluminum-Alloy–Co Composites

This study aimed at the preparation of a 2024 aluminum alloy (2024Al) matrix composite with high strength, high toughness and high magnetic properties that can be used in practical applications. Therefore, Nd2Fe14Bp/2024Al–Co composites with different Co contents (wt.%) were prepared by ball milling, cold isostatic pressing and microwave sintering. The effects of the Co content on the microstructure, mechanical properties and magnetic properties of the prepared composites were studied. Under the conditions of the sintering temperature of 490 °C, heating rate of 20 min/°C and soaking time of 30 min, it was found that with the increase in Co content (0→2.5%→5%→7.5%→10%), the grain size first decreased and then increased, and reached the optimal value of about 3–5 μm when the Co content was 7.5%, with the microstructure being relatively uniform. At the same time, the compactness of the composite arrived at a maximum of 95.4%. The main particle phases in the composite were Nd2Fe14B, Nd2 (Fe, Co)14B and Co particles. In the nanoindentation test, the interface strength of the 7.5% Co sample was significantly higher than that of the Co-free sample. In addition, the microhardness, yield strength and compressive strength of the 7.5% Co sample were 152 HV, 210 MPa and 269 MPa, respectively, which increased by 67%, 78% and 75%, respectively, compared with the Co-free sample. With the increase in Co content, the remanence (Br), coercivity (Hcj) and maximum magnetic energy product ((BH) max) of the composites first increased and then decreased. When the Co content was 7.5%, the three performance indicators reached their optimum values, which were Br: 0.20 (T), Hcj: 4.6 (kOe) and (BH)max: 28.36 (kJ/m3). The expected goal of the lightweight magnetic materials was achieved, and the action mechanism of Co addition in the composites was also analyzed in detail.