Mischmetal cobalt permanent magnet alloys

Abstract

The phase relation study of the MM-Co system reveals that its phase diagram is very similar to that of the Ce-Co system. In the ternary MM-Co-Fe, except the 2:17 phase, the other phases have only limited solid solubility for Fe. Fe can be substituted for Co only up to about 17% in MMCo₅ , whereas Cu has 100% solid solubility. The MMCo₅ phase undergoes a eutectoid type reaction at 700°C and Fe in MMCo₅ increases its instability. The intrinsic magnetic properties measured for the CeCo₅, LaCo₅, SmCo₅ and MMCo₅ indicate possibilities of tailor-making new MM compositions to obtain better magnetic properties. The elements Pr and Nd seem to be attractive to improve B_r and Sm to increase the coercivity of MMCo₅. The results summarised for the permanent magnet properties of MMCo₅ magnets show that the process parameters play a greater role in determining the permanent magnet properties than the alloy composition. A high alignment factor of the powder compact and a min. oxygen content ( < 5000 ppm) of the magnet are imperative to achieve greater value for B_r of the magnet. The Fe addition improves B_r and the Cu gives better _i H_c; both together save the consumption of scarce Co, facilitating fabrication of cheaper permanent magnets.