Tdk Corporation

Tomomi Yamamoto

Takeshi Sakamoto

Yasuyuki Nakayama

Tetsuya Hidaka

Tatsuhiro Iwai

Akira Fukuno

Tetsuhito Yoneyama

Kazuya Sakamoto

Hironari Okada

The permanent magnet memberfor a voice coil motor (VCM) in accordance with the present invention comprises a magnet bodyincluding a shorter periphery, a longer peripherylocated at a position separated from the shorter peripheryby a predetermined distance, and a pair of side peripheriesconnecting the shorter peripheryand longer peripheryto each other, the magnet body having a fan-shaped planar form; and a corrosion-resistant film (Ni plating film) applied to a surface of the magnet body. The permanent magnet memberhas a thickness whose maximum and minimum values yield a difference of 10 to 150 &#x3bc;m therebetween.

Permanent magnet member for coil motor and voice coil motor

A magnet bodyincluding a shorter periphery, a longer peripherylocated at a position separated from the shorter peripheryby a predetermined distance, and a pair of side peripheriesconnecting the shorter peripheryand longer peripheryto each other, the magnet body having a fan-shaped planar form; and a corrosion-resistant film (Ni plating film) applied to a surface of the magnet body. The permanent magnet memberhas a thickness whose maximum and minimum values yield a difference of 10 to 150 &#x3bc;m therebetween.

Provided are a method of manufacturing a rare-earth magnet with superior corrosion resistance, and a plating bath used for the method. A first protective film including nickel and a second protective film including nickel and sulfur are laminated in order on a magnet body including a rare-earth element. The first protective film is formed through electroplating with a first plating bath including a nickel source, a conductive salt and a pH stabilizer, and having a concentration of the nickel source of 0.3 mol/l to 0.7 mol/l on a nickel atom basis and a conductivity of 80 mS/cm or over. Thereby, a rare-earth-rich phase can be prevented from being leached out, and the production of pinholes can be reduced. Therefore, the corrosion resistance of the rare-earth magnet can be improved.

Method of manufacturing rare-earth magnet, and plating bath

An R-T-B system permanent magnetcomprises a magnet bodycomprising a sintered body comprising at least a main phase comprising RTB grains (wherein R represents one or more rare earth elements, and T represents one or more transition metal elements including Fe or Fe and Co essentially) and a grain boundary phase containing R in a larger amount than the main phase, the magnet bodyhaving a 300 &#x3bc;m or less thick (not inclusive of zero thick) hydrogen-rich layerhaving a hydrogen concentration of 300 ppm or more formed in the surface layer portion, and an overcoatcovering the surface of the magnet bodycan improve the corrosion resistance of the R-T-B system permanent magnetwith an overcoatformed thereon without degrading the magnetic properties thereof. The present invention can be applied to formation of the overcoatby electrolytic plating, can fully ensure the corrosion resistance as a primary target of the overcoatformation without substantially degrading the production efficiency, and can provide the R-T-B system permanent magnetwith a high dimensional precision by suppressing the partial collapse (detachment of grains) of the surface thereof.

R-T-B system permanent magnet

An object of the invention is to provide an inexpensive magnet having a high coercivity, high squareness ratio and high maximum energy product. According to the invention, a magnet containing R, T, N, and M wherein R is at least one rare earth element with essential samarium, T is iron or iron and cobalt, and M is at least one element of Ti, V, Cr, Nb, Hf, Ta, Mo, W, Al, C, and P, with essential zirconium, in amounts of 4-8 at % of R, 10-20 at % of N, 2-10 at % of M, and having a hard magnetic phase (TbCu.sub.7 type crystalline phase) and a soft magnetic phase (which is a bcc structured T phase, has an average grain diameter of 5-60 nm, and accounts for 10 to 60% by volume of the entirety), the atomic ratio (R+M)/(R+T+M) in the hard magnetic phase being in excess of 12.5%, is prepared utilizing a single roll technique. In the single roll technique, the peripheral speed of a chill roll is at least 50 m/s, and the discharge pressure of the molten alloy is 0.3-2 kgf/cm.sup.2. Following quenching, the quenched alloy is subjected to heat treatment at 600-800.degree. C. and then to nitriding treatment.

Preparation of magnet

A magnet consists essentially of 4-8 at % of R, 10-20 at % of N, 2-10 at % of M, and the balance of T wherein R is at least one rare earth element, Sm being present in R in a proportion of at least 50 at %, T is Fe or Fe and Co, M is Zr with or without partial replacement by at least one element of Ti, V, Cr, Nb, Hf, Ta, Mo, W, Al, C, and P. Contained in the magnet are a hard magnetic phase based on R, T, and N and containing at least one crystalline phase selected from TbCu.sub.7, Th.sub.2 Zn.sub.17, and Th.sub.2 Ni.sub.17 types and a soft magnetic phase consisting of a T phase having a bcc structure, the soft magnetic phase having a mean grain size of 5-60 nm and being present in a proportion of 10-60% by volume. This construction ensures high coercivity, high squareness ratio, and high maximum energy product.

Growing community of inventors

Tokyo, Japan

Tomomi Yamamoto