Soft-Magnetic High-Entropy AlCoFeMnNi Alloys with Dual-Phase Microstructures Induced by Annealing

Abstract

The simultaneous enhancement of magnetic and mechanical properties is desirable but challenging for soft-magnetic materials. A fabrication strategy to meet this requirement is therefore in high demand. Herein, bulk equiatomic dual-phase AlCoFeMnNi high-entropy alloys were fabricated via a magnetic levitation induction melting and casting process followed by annealing at 700–1000 °C, and their microstructures as well as mechanical and magnetic properties were investigated. The as-cast alloy possessed a single metastable B2-ordered solid solution that decomposed upon annealing into a dual-phase structure comprising an Al- and Ni-rich body-centered cubic (BCC) matrix and Fe- and Mn-rich face-centered cubic (FCC) precipitates both in the grain interior and along the grain boundaries. The magnetic and mechanical properties were closely related to the relative volume fraction of FCC in the alloy. The FCC volume fraction could be increased by increasing the annealing temperature, thereby offering tunable properties. The optimal annealing temperature for balanced magnetic and mechanical properties was found to be 800 °C. The alloy annealed at this temperature had an average BCC grain size of 12 ± 3 μm and FCC volume fraction of 41 ± 4%. Correspondingly, the saturation magnetization and coercivity reached 82.57 Am2/kg and 433 A/m, respectively. The compressive yield strength and fracture strength were 1022 and 2539 MPa, respectively, and the plasticity was 33%. Owing to its adjustable microstructure and properties, the AlCoFeMnNi alloy has potential for use as a multi-functional soft-magnetic material.