Mischmetal cobalt permanent magnet alloys

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 Br 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 Br of the magnet. The Fe addition improves Br and the Cu gives better i Hc; both together save the consumption of scarce Co, facilitating fabrication of cheaper permanent magnets