Patent ID: 6254694
Filing Date: 2001-07-03
Classification: H01F,H02K

Abstract:
A method for producing an R--T--B-based, permanent magnet, wherein R is one or more of rare earth elements including Y, and T is Fe, part of which may be substituted by Co, said permanent magnet having:(a) a corrosion-resistant layer located on the surface of said permanent magnet, wherein said corrosion-resistant layer is formed by electroplating or electroless plating and is made of a metal or alloy of at least one element selected from the group consisting of Zn, Cr, Ni, Cu, Sn, Pb, Cd, Ti, W, Co, Al, and Ta, or being made of a compound of at least one element selected from the group consisting of Zn, Cr, Ni, Cu, Sn, Pb, Cd, Ti, W, Co, Al, and Ta, and at least one element selected from the group consisting of C, P, S, N, and O; and(b) a main phase of R.sub.2 Fe.sub.14 B and a layer richer in rare earth elements than said main phase, wherein said layer richer in rare earth elements is located beneath said corrosion-resistant layer;said R--T--B-based, permanent magnet being formed from an alloy having a composition by weight of 20-45% R, 0.5-6% B, 0.1-15% Co, 5% or less Cu, 0.5-10% at least one additive element selected from the group consisting of Al, Si, Nb, Mo, V, Mn, Sn, Ni, Zn, Ti, Cr, Ta, W, Ge, Zr, Hf, and Ga, and the balance being Fe,said method comprising:(1) forming said corrosion-resistant layer on a surface of a sintered magnet having said composition of R--T--B; and(2) subjecting said sintered magnet provided with said corrosion-resistant layer to a heat treatment at a temperature of 400-700.degree. C. in an inert or non-oxidizing atmosphere or in vacuum, such that said layer richer in rare earth elements than said main phase of R.sub.2 Fe.sub.14 B is generated beneath said corrosion-resistant layer.