Process for producing, through strip casting, raw alloy for nanocomposite type permanent magnet
View Patent ↗To make a raw alloy, consisting mostly of amorphous structure, highly productively and at a reduced cost for a nanocomposite magnet, a molten alloy represented by Fe 100-x-y-z R x Q y M z (where R is at least one element selected from Pr, Nd, Dy and Tb; Q is B and/or C; M is at least one element selected from Co, Al, Si, Ti, V, Cr, Mn, Ni, Cu, Ga, Zr, Nb, Mo, Ag, Pt, Au and Pb; and 1 at %≦x<6 at %, 15 at %≦y≦30 at % and 0 at %≦z≦7 at %) is prepared. This molten alloy is rapidly cooled by a strip casting process in which the alloy is fed onto a chill roller, rotating at a peripheral velocity of 3 m/s to less than 20 m/s, at a feeding rate per unit contact width of 0.2 kg/min/cm to 5.2 kg/min/cm. In this manner, an alloy including at least 60 volume percent of amorphous phase can be obtained.
1. A method of making a raw alloy for a magnet, the method comprising the steps of:
preparing a molten alloy represented by Fe 100-x-y-z R x Q y M z where R is at least one element selected from the group consisting of Pr, Nd, Dy and Tb; Q is B and/or C; M is at least one element selected from the group consisting of Co, Al, Si, Ti, V, Cr, Mn, Ni, Cu, Ga, Zr, Nb, Mo, Ag, Pt, Au and Pb; and x, y and z satisfy 1 at %≦x<6 at %, 15 at %≦y≦30 at % and 0 at %≦z≦10 at %; and
obtaining a thin-strip alloy, including an amorphous structure, by a strip casting process, in which the molten alloy is brought into contact with a chill roller within a vacuum or in a reduced pressure atmosphere so as to have a predetermined contact width in an axial direction of the chill roller and in which the molten alloy is moved along an outer circumference of the chill roller and cooled by rotating the chill roller;
wherein the chill roller is rotated at a peripheral velocity of 3 m/s to less than 20 m/s, and
wherein the molten alloy is continuously fed onto the chill roller at a feeding rate per unit contact width of 0.2 kg/min/cm to 5.2 kg/min/cm.
2. The method of claim 1 , wherein the molten alloy is fed onto the chill roller at a feeding rate of at least 3 kg/min.
3. The method of claim 1 or 2 , wherein the molten alloy is brought into contact with the chill roller by way of a shoot, the shoot controlling the flow of at least a portion of the molten alloy toward the chill roller, and
wherein the shoot includes a plurality of melt drains, each of which is located in the vicinity of the chill roller and which has a predetermined teeming width as measured in the axial direction of the chill roller, and
whereby multiple thin-strip alloys are made from the molten alloy that has passed through the melt drains and contacted with the chill roller.
4. The method of claim 1 , wherein the predetermined contact width is 0.5 cm to 10.0 cm.
5. The method of claim 1 , wherein the thin-strip alloy has a metal structure that includes at least about 60 volume percent of amorphous structure.
6. The method of claim 1 , further comprising the step of continuously crushing the thin-strip alloy and collecting the crushed alloy such that a tap density thereof becomes at least equal to 1 g/cm 3 .
7. A magnet raw alloy prepared by the method of claim 1 , wherein the raw alloy has a coercivity H cJ of at most 10 kA/m before being heated and crystallized.
8. The raw alloy of claim 7 , wherein the raw alloy has a thickness of 70 μm to 250 μm.