Investigations into the optimisation of the commercial processing route for Sm₂CO₁₇ type permanent magnets

The increasing use of permanent magnet motors in demanding high temperature environments has led to a renewed research interest into Sm₂CO₁₇ type magnets in recent years. This work has investigated key points in the commercial production route of a sintered magnet with composition Sm(Co\(_{0.7}\)Fe\(_{0.21}\)Cu\(_{0.07}\)Zr\(_{0.02}\))\(_{7.61}\), with an aim to establish if the current heat treatment route can be optimised. Through small alterations to Sm content, it was found that a high knee field (H\(_k \)) of ~1700 kAm\(^{-1} \) and high remanence (B\(_r\)) of 1.13 T could be achieved in a Sm(Co\(_{0.7}\)Fe\(_{0.21}\)Cu\(_{0.07}\)Zr\(_{0.02}\))\(_{7.77}\) sintered alloy, a particularly Fe rich composition, after quenching directly from the aging temperature. This suggests high remanence magnets, with good coercivity, could be produced without the requirement for the controlled 'slow cool', shortening production time per batch by ~7-10 hours. Strip casting was investigated as an alternative to ingot casting in the production of the starting alloy for sintered magnets. If a structure of large grains of the 1:7 phase could be produced, the homogenisation step would be unnecessary. A wheel speed of 1.6 ms\(^{-1}\) with an F8-grit textured wheel, did not produce a single 1:7 phase, and the grain structure was too fine. Grain coarsening heat treatments had limited success.