Effect of Thermal Treatment on Formation of High Magnetic Parameters of Sintered Magnets Dd-Fe-B

The present paper is dedicated to study effect of thermal treatment parameters on the properties (residual magnetic induction fir, coercive force on magnetization iHc, temperature coefficient of magnetic induction αb within the temperature range 300–373 K) of sintered permanent magnets [Dd1–x(Dy, Tb, Ho)x]15(Fe1–yCoy)bal(Al,Cu,Ga,Ti)0.1–1.4B5.0–8.5 (at.%), where x=0.2–0.4; y = 0.2–0.3; Dd - didymium. For the magnets (Dd1–xDyx)15(Fe1–yCoy)baiB5.0–5.6 discontinuities were observed at demagnetization curves caused by appearance of magnetic phases with reduced magnetic anisotropy. iHc value nearly does not depend on temperature of thermal treatment within the range 750–1275 K at increasing of boron content (7.0–7.5at.%). Magnets doping by such elements as aluminium, copper, gallium shifts optimal temperature of the last step of thermal treatment from 900 K to 725–825 K, at the same time magnetic properties (Br, iHc αb) improve, especially with increasing of Co and Dy content. It was possible to attain the following properties for the magnets (Dd0.6Dy0.4)15(Fe0.74Co0.26)bai(Al,Cu,Ga)1.1B8.5 after optimal thermal treatment {1175 K (7, 2 ks) with further cooling at the rate 1–2 K/min, then 900 K (3.6 ks) - hardening + 775 K (3.6 ks) - hardening}: Br= 1,0 T, iHc = 1600 kA/m, BHmax = 192 kJ/m3, αb= −0,024 %/K in the temperature interval 293–373 K.