1The Research Institute of Electric and Magnetic Alloys, 2 Yagiyama-minami, Sendai 982
The thermal expansion and thermomagnetization of Mn-16~22%Ge-misch metal alloys comprising chiefly a (γ +ε ) mixture phase were investigated in the temperature range from 120 to 570 K. Hardness measurements and turning and forging tests were carried out at room temperature. Compared with the experimental results and crystal structures, the relationship between machinability and structures was investigated.
The thermal expansivity of the ternary alloys containing less than 1%misch metal is identical to that observed in the base alloys. While the magnetization of these alloys exhibits a small value, it rapidly increases with increase of misch metal content. When the Vickers hardness of these alloys is 50~100 lower than that of the binary alloys by the addition of misch metal, the cutting capacity and forginability are improved. In the ternary alloys with misch metal, needle-like precipitates were observed in the grains and across the boundaries. It has become obvious that the higher machinability of the alloys with misch metal arises from the pinning effect of an appropriate amount of the precipitates. In particular, the Mn-19%Ge-0.5~1.0%misch metal alloys are desirable because of their remarkable Invar characteristics, small values of magnetization and good machinability.
Invar, thermal expansion, manganese-germanium based alloys, misch metal, antiferromagnetism, magnetization, machinability, hardness
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