The performance of electrical machines – vital for emerging technologies like wind power, electric vehicles, fully automized industrial machines, and robots – requires functional materials with a high energy density (BH)_max such as rare earth permanent magnets (PMs). Due to their outstanding properties for most applications sintered (Nd,Dy)FeB- type PMs are the material of choice, while for specific high temperature applications, like electric motors, sintered SmCo type magnets are used. Due to the mentioned applications both materials are used in large numbers, and for this reason the dependence on the necessary critical raw materials in EU magnet industry and key technologies will increase seriously.

A possible strategy to increase the energy density (BH)_max of SmCo magnets and at the same time reducing the criticality is the partial substitution of Co by Fe, an approach already established but possible only up to a certain ratio, while for higher substitution further microstructure adjustments are required. In order to create such an improved microstructure we investigated an alternative casting technology, strip casting, instead of the established ingot casting procedure.

In this contribution, we show results from the BMBF funded research project HOMAG. Here, strip casting was carried out to produce flake precursor for SmCo based magnets for the first time. By using the strip casting technology, a controlled and fast solidification of the melt on a water-cooled copper wheel is established. Hence, metastable phases can be stabilized. Parameters were varied during the casting process and permanent magnets out of this material were synthesized and investigated in terms of their magnetic properties. It is found that magnets made from strip cast materials did not exceed the properties of those of state-of-the-art book mold alloys yet. Microstructural investigations ranging from the cast flakes over the further processing steps (i.e. milling, aligning) into the dense magnet were carried out. In contrast to NdFeB – where strip casting is beneficial for the microstructure – it was found out that for SmCo this is not the case, which may be attributed to the fundamentally different magnetic hardening mechanism, nucleation vs pinning, and the required different microstructures.