INVESTIGATION OF FABRICATION OF Co-Zr BASED RARE EARTH-FREE HARD MAGNETIC ALLOYS BY MELT-SPINNING METHOD

Abstract

Co-Zr based alloy has attracted much interest of potential to replace the rare earth-containing hard magnetic materials due to its high coercivity. In this study, we investigated the effects of subtituting elements of M (Ti, Si and Nb) and annealing temperature on the structure and magnetic properties of Co79-xZr18+x-yMyB3 alloy ribbons (x = 0 - 2, y = 0 - 4). The alloy ribbons with a thickness of 20 µm were prepared by melt-spinning method with a rolling speed of 40 ms-1. A part of the melt-spun ribbons was annealed at different temperatures from 550 to 800 oC for various durations from 2 to 15 minutes. Their structure and magnetic properties were investigated by X-ray diffraction (XRD) and a pulsed field magnetometer (PFM), respectively. The results of the XRD analysis showed that two soft magnetic phases, namely Co and Co23Zr6, coexist with a Co5Zr hard magnetic phase in the alloy ribbons. The fraction of these phases was changed with both the concentration of the subtituting elements and annealing process. Hard magnetic properties of the alloy ribbons can be strengthened significantly, namely a large coercivity Hc > 4 kOe and maximum energy product (BH)max > 3.5 MGOe were obtained with an appropriate concentration of Ti, Si or Nb and annealing process. Furthermore, the subtituting elements also affect the optimal annealing temperature for these alloys. The obtained strong hard magnetic parameters of these rare earth-free alloys are of great importance in pratical application.