Expandable sintered neodymium-iron-boron magnet, preparation method therefor and application thereof

A preparation method for an expandable sintered neodymium-iron-boron magnet, comprising:

• coating an expandable coating material on a surface of a sintered neodymium-iron-boron magnet;
• and
• performing a pre-curing treatment to prepare the expandable sintered neodymium-iron-boron magnet, wherein the pre-curing treatment comprises drying the coated sintered neodymium-iron-boron magnet at 15-90° C.,
• wherein:
• the expandable coating material comprises the following components in percentage by weight:
• 45%-65% of a water-soluble resin, 10%-30% of a foaming agent, 0.1%-0.5% of hectorite, 0.5%-3% of diethylene glycol butyl ether, 1%-3% of propylene glycol, 0.2%-0.8% of acrylic acid thickener, 0.1%-0.5% of a dispersant, and 0.1%-0.5% of a leveling agent, the water-soluble resin having a solid content of 30%-50%;
• the foaming agent is a plurality of thermoplastic expandable microspheres, each comprising a thermoplastic resin shell and a propellant encapsulated therein, wherein more than 70% of the propellant is one or more selected from isooctane, butane, pentane, and heptane and wherein each of the plurality of thermoplastic expandable microspheres has a diameter of 5-30 μm;
• and
• the expandable coating has a thickness of 50-300 μm,
• wherein:
• in a pressure-free state and when performing a heating expansion treatment at a temperature of 110-210° C., the expandable coating has an expansion rate of 200%-400%,
• wherein the heating expansion treatment is performed by a two-stage heating method comprising a first expansion stage followed by a second expansion stage,
• wherein the first expansion stage is carried out a heating rate of 5-15° C./min to a temperature of 110-160° C.;
• and the second expansion stage is carried out a heating rate of 30-60° C./min to a temperature of 180-210° C.,
• wherein, after expansion of the expandable coating, the plurality of thermoplastic expandable microspheres account for 60%-90% of a cross-sectional area of the expanded coating.