Rare-earth alloy, rare-earth sintered magnet, and methods of manufacturing

A method of manufacturing a rare-earth sintered magnet, comprising the steps of:

• melting an alloy composed mainly of 20 to 30 wt % of a rare-earth constituent R which is samarium alone or at least 50 wt % samarium in combination with at least one other rare-earth element, 10 to 45 wt % of iron, 1 to 10 wt % of copper and 0.5 to 5 wt % of zirconium, with the balance being cobalt;
• quenching the molten alloy in a strip casting process so as to form a rare-earth alloy ingot which has a content of 1 to 200 μm size equiaxed crystal grains of at least 20 vol % and a thickness of 0.05 to 3 mm;
• heat-treating the ingot in a non-oxidizing atmosphere at 1000 to 1300° C. for 0.5 to 20 hours to form a rare-earth magnet alloy;
• milling the rare-earth magnet alloy;
• compression-molding the milled alloy in a magnetic field to form a compact;
• sintering the compact;
• subjecting the sintered compact to solution treatment;
• and
• carrying out aging treatment on the solution-treated compact.

A method of manufacturing a rare-earth permanent magnet, comprising the steps of:

• casting by a strip-casting process an alloy consisting essentially of 20 to 30 wt % of a rare-earth constituent R which is samarium alone or at least 50 wt % samarium in combination with at least one other rare-earth element, 10 to 45 wt % of iron, 1 to 10 wt % of copper and 0.5 to 5 wt % of zirconium, with the balance being cobalt and inadvertent impurities;
• heat-treating the strip-cast alloy in a non-oxidizing atmosphere at 1000 to 1300° C. for 0.5 to 20 hours to form a rare-earth magnet alloy having an average crystal grain size of 20 to 300 μm;
• milling the rare-earth magnet alloy;
• compression-molding the milled alloy in a magnetic field to form a compact;
• sintering the compact;
• subjecting the sintered compact to solution treatment;
• and
• carrying out aging treatment on the solution-treated compact.

A method of manufacturing rare-earth sintered magnets, the method comprising the steps of:

• casting by a strip-casting process an alloy having the compositional formula:
• R(Co(1−a−b−c)FeaCubZrc)z
• wherein R is samarium alone or at least 50 wt % samarium in combination with at least one other rare-earth element, and the letters a, b, c and z are positive numbers which satisfy the conditions 0.1≦a≦0.35, 0.02≦b≦0.08, 0.01≦c≦0.05 and 7.0≦z≦9.0;
• heat-treating the strip-cast alloy at 1100 to 1250° C. for 1 to 20 hours in a non-oxidizing atmosphere to form a rare-earth magnet alloy having a TbCu7-type crystal structure of at least 50 vol %;
• milling the rare-earth magnet alloy;
• compression-molding the milled alloy in a magnetic field to form a compact;
• sintering the compact;
• subjecting the sintered compact to solution treatment;
• and
• carrying out aging treatment on the solution-treated compact.

A method of manufacturing an anisotropic rare-earth sintered magnet having a maximum energy product (BH)max of at least 25 MGOe, the method comprising the steps of:

• heat-treating a Sm2Co17-based permanent magnet alloy consisting essentially of 20 to 30 wt % of a rare-earth constituent R which is samarium alone or at least 50 wt % samarium in combination with at least one other rare-earth element, 10 to 45 wt % of iron, 1 to 10 wt % of copper, 0.5 to 5 wt % of zirconium and 0.01 to 1.0 wt % of titanium, with the balance being cobalt and inadvertent impurities, at 1100 to 1250° C. for 0.5 to 20 hours to give the alloy a TbCu7-type crystal structure content of at least 50 vol %;
• milling the magnet alloy;
• molding the milled alloy to form a compact;
• sintering the compact;
• solution-treating the sintered compact;
• and
• carrying out aging treatment on the solution-treated compact.