Metastable A/sub 1/ phase in Al-doped Nd-Fe-B magnets

The role of metastable A/sub 1/ phase in the coercivity of Al-doped Nd-Fe-B magnets is investigated in a magnet enriched in both Nd and Al. The as-sintered magnet (intrinsic coercive field /sub i/H/sub c/=3.6 kOe) contains an additional phase with Curie temperature T/sub c/=180 degrees C, while the annealed (600 degrees C/1 h) magnet (/sub i/H/sub c/=12.1 kOe) does not. As-cast ternary alloys with compositions Nd-(20-x)at.%Fe-xat.%Al(x=1-10) show the metastable A/sub 1/ phase with reduced T/sub c/, but annealed alloys show the mu and delta phases of the Nd-Fe-Al system. Quaternary Nd-Fe-Al alloys are also studied. The disappearance of the ferromagnetic phase with T/sub c/=180 degrees C is associated with the decomposition of A/sub 1/. The magnetic properties of delta are discussed, and the transformation kinetics of A/sub 1/ are studied.<
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