Synthesis and Magnetic Hysteresis Properties of an Aluminum-Doped Isotropic Hard-Magnetic Fe–Cr–Co Powder Alloy

Abstract—Hard-magnetic Fe–30 Cr–20 Co alloys doped with 1 wt % of aluminum have been obtained. The two different aluminum sources used were elemental aluminum powder and an iron‒chromium‒aluminum alloying composition. Study of the density of the samples has shown that the aluminum additive increases the porosity of the material from 2–3 to 4.5–7%. The highest porosity was observed when using the alloying composition. Differences in the pore structure after sintering under the same conditions depending on the aluminum source have been found. When the alloying composition is used, pores acquire a branched structure, which indicates incomplete sintering. When elemental aluminum powder is used, the pores are distributed more uniformly and their shape becomes closer to spherical. According to the X-ray diffraction data, when the alloying composition is used, the material contains traces of the nonmagnetic γ and σ phases after a complete processing cycle. It is shown that aluminum doping of the Fe–30 Cr–20 Co alloy does not improve the magnetic properties and the use of the alloying composition degrades them, mainly the residual induction B_r. The investigated alloys have been found to be sensitive to the heat treatment conditions. The highest magnetic characteristics are B_r = 0.66 T, H_c = 43.2 kA/m, and (BH)_max = 10.2 kJ/m³ with the alloying composition used and B_r = 0.85 T, H_c = 46.7 kA/m, and (BH)_max = 15.1 kJ/m³ with the elemental powder used. During the compression tests, the investigated alloys have been deformed without fracture up to the maximum strain degree of ε = 17.5–20% and have exhibited high yield strengths: σ_0.2 = 1050–1250 MPa.