THE ROLE OF AL IN RAPIDLY SOLIDIFIED FEPRBAL PERMANENT-MAGNETS

Magnetic and microstructural investigations were performed on melt-spu n permanent magnets of compositions Fe78-xPr15B7Alx to check the influ ence of the addition of Al on melt-spun FePrB-based permanent magnets. The microstructural parameters alpha(K) and N(eff), which describe th e effects of the non-ideal microstructure, were determined from the te mperature dependence of the critical field. Both parameters show signi ficant increases with increasing Al concentration, i.e. the improvemen t of the grain surfaces is compensated by increased local demagnetizat ion fields. Long annealing treatments lead to a deterioration of the h ard magnetic properties; this is correlated with an increase in the N( eff) parameter and a nearly constant alpha(K) value. These magnetic re sults were compared with SEM investigations carried out on cross-secti ons of the melt-spun ribbon flakes.