Bulk magnetic hardening in Cu-added (SmCo5)1-x(Sm2Co17)x cast alloys*

In attempt to establish a possible link between the magnetic hardening in Sm(Co,Cu)$_{5}$ magnets and the commercial "2:17" magnets, we have investigated a series of homogenized ternary Sm-Co-Cu alloys with composition between Sm(Co,Cu)$_{5}$ and Sm$_{2}$Co$_{17}$. The coercivity of the alloys with x $<$ 0.75 can be increased by isothermal aging without separation into 1:5 and 2:17 phases. The increase in coercivity is accompanied by an increase in the Curie temperature. A similar effect of low-temperature aging has also been observed in Sm-Co-Ni, Sm-Co-Fe-Cu and Pr-Co-Fe-Cu alloys. A different pattern of magnetic hardening can be observed in the alloys with $x \quad >$ 0 which were slowly cooled from 800 to 350 $^{o}$C. In this case, the initial hexagonal structure transforms into the cellular structure of the 1:5 and 2:17 (rhomb.) phases. In the alloy with x = 0.25, the two types of magnetic hardening may lead to the same room temperature coercivity despite the very different microstructures. The correlation between the observed microstructures and coercivity will be discussed.