Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
  • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
  • H01F1/047—Alloys characterised by their composition
  • H01F1/053—Alloys characterised by their composition containing rare earth metals
  • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
  • H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
  • H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
  • H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
  • H01F1/0577—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together sintered
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/10—Sintering only
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/10—Ferrous alloys, e.g. steel alloys containing cobalt
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
  • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
  • H01F1/047—Alloys characterised by their composition
  • H01F1/053—Alloys characterised by their composition containing rare earth metals
  • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
  • H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B

Definitions

• the present invention relates to a sintered rare earth magnet having high magnetic properties and excellent corrosion resistance.
• Sintered rare earth magnets are functional materials which are necessary and indispensable for greater energy efficiency and higher functionality, and their range of use and production volume are growing from year to year.
• sintered rare earth magnets in particular have a high residual magnetic flux density (also referred to below as B r ) and are being used in a variety of applications and environments, including drive motors for hybrid cars and electric cars, power steering motors, air conditioner compressor motors, and voice coil motors (VCM) for hard disk drives.
• B r residual magnetic flux density
• VCM voice coil motors
• Patent Document 1 JP-A 2007-300791 discloses a method which, by forming an electroplated nickel film on the magnet surfaces, imparts high corrosion resistance that enables use even in water.
• Patent Document 2 JP-A 2020-102551 discloses art which, by having copper be present at the grain boundaries in such a way that the concentration gradient decreases from the surface of the magnet towards the interior and by providing an oxide layer at grain boundaries in regions at a depth of 0.1 to 5 ⁇ m from the surface, enhances the corrosion resistance of the magnet within a water pump.
• JP-A 2021-61301 states that a high corrosion resistance can be achieved by forming a microstructure in which the rare earth element content of the magnet's grain boundary phases overall is at least 55 wt% and copper-rich regions containing at least 8 wt% copper account for at least 9 vol% of the grain boundary phases.
• the present invention was conceived in light of the above issues.
• the object of the invention is to provide a sintered rare earth magnet which has high magnetic properties and excellent corrosion resistance by forming a region of specific composition at the surface of the magnet.
• the inventors have conducted repeated and intensive investigations focused on the composition of sintered rare earth magnets, especially the relationship between the contents of R elements and M elements (cobalt, copper, gallium) that contribute to the formation of grain boundary phases in a specific region near the surface of the magnet.
• R elements and M elements cobalt, copper, gallium
• this invention provides the following sintered rare earth magnet.
• This invention makes it possible to obtain sintered rare earth magnets which can be conferred with high corrosion resistance without the formation of a protective film by a post-treatment step, and which are outstanding in terms of cost because a grain boundary diffusion step using heavy rare earth elements is not always necessary.
• FIG. 1 is a graph showing the relationship between the [R GB ]/[M1] value and percent weight loss in Examples according to the invention and Comparative Examples.
• the R content is not more than 17 at%, more preferably not more than 15.5 at%, and even more preferably not more than 15 at%.
• the proportion of neodymium in R is not particularly limited, although it is preferably at least 60 at%, and more preferably at least 75 at%, of all the R elements.
• R elements other than neodymium, although elements such as praseodymium, dysprosium, terbium, holmium, erbium, samarium, cesium and yttrium may be preferably included.
• the iron serves as the balance of the composition other than the above constituents R, boron, M1, M2 and oxygen.
• the iron content is preferably at least 70 at%, and more preferably at least 75 at%.
• the iron content is not particularly limited, although to keep the squareness from worsening due to the precipitation of R 2 T 17 phases and to keep the H cJ from decreasing, it is preferably not more than 82 at%, and more preferably not more than 80 at%.
• the boron content is preferably 5.0 at% or more, more preferably 5.5 at% or more, and even more preferably 5.7 at% or more. Within such a range, the proportion of the R 2 T 14 B phase that forms becomes low, and so a large decrease in B r and worsening of the squareness due to the formation of R 2 T 17 phases can be suppressed.
• the upper limit is preferably not more than 7.0 at%, more preferably not more than 6.5 at%, and even more preferably not more than 6.3 at%. Within such a range, a R 1.1 T 4 B 4 compound phase forms and decreases in B r and H cJ are easily avoided. Some of the above boron may be substituted with carbon.
• M1 is two or more elements selected from cobalt, copper and gallium, with cobalt being essential.
• M1 is two or more elements selected from cobalt, copper and gallium, with cobalt being essential.
• the content of M1 is preferably at least 1.0 at%, and more preferably at least 1.5 at%. In this way, the formation of compounds of R and M1 is sufficiently carried out, enabling the formation of R metal phases having a high R concentration to be suppressed and thus resulting in improved corrosion resistance.
• the upper limit is preferably not more than 3.5 at%, and more preferably not more than 3.0 at%. This enables decreases in B r and H cJ to be suppressed.
• the above cobalt may take the place of some of the iron included in the R 2 T 14 B phase and the grain boundary phases.
• the content of cobalt is preferably at least 0.5 at%, and more preferably at least 1.0 at%, of the overall magnet.
• the cobalt content is preferably not more than 3.0 at%, and more preferably not more than 2.0 at%.
• the content of copper is preferably at least 0.1 at%, and more preferably at least 0.2 at%, of the overall magnet.
• the copper content is preferably not more than 1.0 at%, and more preferably not more than 0.5 at%.
• formula (4) below is additionally satisfied in the high corrosion resistance region.
• Cu + Ga ⁇ 0.28 This [Cu] + [Ga] value, from the standpoint of obtaining an optimal temperature range in heat treatment to ensure good productivity and from the standpoint of obtaining a corrosion resistance enhancing effect, is preferably at least 0.28, and more preferably at least 0.35. Although there is no particular upper limit, to stably obtain a high B r , this value is preferably not more than 1.50, and more preferably not more than 1.00.
• the microstructures of the resulting magnets were examined with an electron probe microanalyzer (EPMA).
• the R metal phases were identified from backscattered electron images and the results of semiquantitative analysis, and the proportion of R metal phase included in all the grain boundary phases of the magnet was measured by image processing. The results are shown in Table 2.
• Magnets were manufactured in the same way as in Example 1. Metal constituent analysis was carried out on the resulting magnets using ICP-OES. In addition, the oxygen concentration was measured by the inert gas fusion infrared absorption method, the nitrogen concentration was measured by the inert gas fusion thermal conductivity method, and the carbon concentration was measured by the combustion infrared absorption method. The results are presented in Table 5. The proportion of R metal phases and the percent weight loss in the corrosion resistance evaluation test were calculated in the same way as in Example 1. The results are shown in Table 6. Table 6 also shows the formula (3) and (4) calculated values specified in the invention. In Examples 7 to 12 and Comparative Example 7, grain boundary diffusion treatment was not carried out and so it is assumed that there was no change in the concentration gradient from the magnet surface to the interior.
• the average compositions of R, iron, cobalt, copper and gallium in the range in depth of 0.1 to 200 ⁇ m from the surface were substituted with the contents of the metal elements included in the overall magnet as determined above by ICP-OES analysis.
• the region for which this was done was the entire surface of the magnet.
• Terbium metal, electrolytic iron, electrolytic cobalt and gallium metal were weighed out and blended in atomic ratios of 1:1:1 and these raw materials were melted in an arc melting furnace to give TbFeGa and TbFeCo alloy ingots, following which the alloy ingots were heat treated for 10 hours at 1050°C in a vacuum atmosphere.
• the heat-treated alloy ingots were milled in a ball mill, preparing alloy powders having a D50 of about 10 ⁇ m.
• the alloy powder was mixed together with a water-soluble PVA resin slurry in a 7:3 ratio and stirred, then formed to a thickness of 50 ⁇ m and dried, thereby fabricating TbFeGa alloy sheets and TbFeCo alloy sheets.
• magnets similar to that in Comparative Example 1 were manufactured.
• the magnets thus obtained were cut to dimensions of 17 mm (L) ⁇ 19 mm (W) ⁇ 2.2 mm (T), TbFeGa alloy sheets (Example 13) and TbFeCo alloy sheets (Example 14) were attached to the LW faces perpendicular to the direction of magnetization, following which the magnet was held at 900°C for 20 hours in a vacuum atmosphere and then slowly cooled to 300°C. The temperature was subsequently raised to 450°C and the magnet was held at that temperature for 2 hours, after which it was rapidly cooled to 300°C.
• FIG. 1 shows a graph of the relationship between [R GB ]/[M1] and the weight loss ratio in Examples 1 to 14 and Comparative Examples 1 to 7.
• the Examples according to the invention are indicated by closed circles ( ⁇ ) and the Comparative Examples are indicated by closed triangles ( ⁇ ). From this graph, it is apparent that when the value of [R GB ]/[M1] is 2.4 or more, the corrosion resistance worsens. On the other hand, when the value of [R GB ]/[M1] is 1.0 or less, the corrosion resistance is good, but the magnetic properties worsen (Comparative Examples 5 and 6). Also, in a case where the value of [R GB ]/[M1] satisfies formula (3) but formula (4) is not satisfied, the corrosion resistance worsens (Comparative Example 7).

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• 2024
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