Effect of Temperature Gradient on the Microstructure of the Rapidly Solidified Nd–Fe–B Strips

High-performance Nd-Fe-B magnets with nominal composition of Nd_13.25Dy_0.2Fe_78.87Co₁Cu_0.1Al_0.5B_6.08 (at%) have been produced by using strip casting technique. It was found that the temperature gradient of alloy in the solidification stage determines the grain size and the grain alignment of the alloy strips. The growth direction of grains parallels the direction of heat flow during solidification stage. The average solidifying rate of strips is more than 10³°C/s, which can effectively depress the formation of α-Fe dendrites. It is observed that the concentration of rare earth has a significant decrease from free side to wheel side of the strip. The results of magnetic properties of final magnets produced with different strips indicate that the nonuniform phase structure can deteriorate the squareness of demagnetization curve and the temperature coefficient of coercivity. Effects of the temperature gradient in the solidification process on the microstructure of alloy strips, magnetic properties, and thermal stability of the final magnets are investigated systematically.