钕铁硼烧结磁体如何制造：从合金到充磁的八步工艺

How are neodymium magnets made? Not the way ordinary metal parts are. They are built from powder, pressed in a magnetic field, and fused in a vacuum furnace. By the end of this guide you will know each step in order, from molten alloy to a magnetized part, why high-temperature grades lean on heavy elements like dysprosium, and where almost all of this work happens today. You will also see why the midstream steps that turn neodymium oxide into metal and alloy are the hardest to copy outside the dominant producer.

Table of Contents

• What is a sintered NdFeB magnet?
• How are neodymium magnets made? The process step by step
• Why high-temperature grades need heavy rare earths
• Where are most rare earth magnets made?
• Why the oxide-to-metal-to-alloy steps are the real bottleneck
• Frequently asked questions

What is a sintered NdFeB magnet?

A sintered NdFeB magnet is a dense, fused block built around a single tetragonal crystal phase with the formula Nd2Fe14B. That phase gives the magnet its strength. The alloy is mostly iron, with a large fraction of rare earths and a small amount of boron, plus trace additions of metals like cobalt, copper and aluminum. Makers press fine alloy powder into shape, then heat it in a vacuum until the particles bond into a solid body. The sintered route produces full-density magnets with the highest performance. The other main route, bonded magnets, mixes magnet powder with a polymer binder and trades strength for shape freedom. See the key figures table on this page for the recipe ranges.

The tetragonal crystal at the core of the magnet

The magnet's power comes from the Nd2Fe14B tetragonal crystal structure. Every processing step exists to grow and align that phase correctly. The history of the neodymium magnet (opens in a new tab) traces to two independent developments, one using a melt-spun method and one using the full-density sintered method described here.

What goes into the alloy

The bulk of the alloy is iron, with rare earths making up roughly a third by weight and boron close to one percent. Neodymium-praseodymium is the main rare earth input. Small additions of cobalt, copper and aluminum tune the magnet's behavior. Heavy elements such as dysprosium and terbium are added in smaller shares for grades that must run hot. The full recipe breakdown from JDA Magnet (opens in a new tab) lists the typical weight ranges, which appear in the key figures table on this page.

Sintered versus bonded magnets

Sintered magnets are fused solid and reach the highest energy products. Bonded magnets hold powder in a binder, which lets makers mold complex shapes but lowers the magnetic strength. This guide follows the sintered route from start to finish.

How are neodymium magnets made? The process step by step

The short answer: molten alloy is cast into thin flakes, broken and milled into fine powder, pressed in a magnetic field, fused in a vacuum furnace, machined to size, coated against corrosion, and finally magnetized. Each stage has tight targets. The strip is cast only a few hundred micrometers thick. The powder is milled to a few micrometers. Compacts are pressed to a set density, then shrink substantially during sintering, which forces a final grinding step. A protective plating goes on before the part ever sees a magnetic field. The magnetizing pulse comes last, delivered in a single capacitor discharge. The figures for each step appear in the key figures table on this page.

Step 1: Vacuum melting and strip casting

Raw metals are melted in a vacuum furnace and poured onto a cooled wheel that casts them into thin strips. Strip thickness controls the final structure. Thin strips in the preferred range give a clean grain structure, while thicker strips let unwanted alpha-iron form. The target thickness sits in the key figures table on this page.

Step 2: Hydrogen decrepitation

The cast strip is placed in a vacuum rotary furnace, where it absorbs hydrogen and then releases it. The strip cracks apart into a coarse powder. This breaks the alloy down without heavy mechanical grinding.

Step 3: Jet milling to a fine powder

A high-speed nitrogen gas flow drives the coarse powder through a jet mill. Particles collide and shatter into a fine powder a few micrometers across. The process flow from HGT Advanced Magnets (opens in a new tab) gives the powder sizes, listed in the key figures table on this page.

Step 4: Pressing in an aligning magnetic field

The fine powder is pressed inside an applied magnetic field, which lines up the particles so their easy axis points one way. Mold pressing brings the compact to a first density. Isostatic pressing then raises it further. These density targets appear in the key figures table on this page.

Step 5: Vacuum sintering and heat treatment

The pressed green compacts go into a vacuum furnace and fuse at high temperature. The particles bond into a solid, full-density body. Two annealing stages follow at lower temperatures to set the final magnetic properties. The sintering and annealing ranges sit in the key figures table on this page.

Step 6: Machining

Sintered blocks shrink by a noticeable amount during firing, so they come out undersized and uneven. Diamond grinding brings each block to its final dimensions. The full process from Radial Magnets (opens in a new tab) gives the shrinkage and the standard tolerance, both in the key figures table on this page.

Step 7: Coating

Bare sintered NdFeB corrodes easily, especially along its grain boundaries. A plated layer seals the surface. Common choices are nickel, nickel-copper-nickel and zinc. The typical thickness of a nickel-copper-nickel coating is in the key figures table on this page.

Step 8: Magnetizing and inspection

A coated part is not yet a magnet in the field sense. It becomes one when a capacitor bank discharges through a fixture coil and hits the part with a short, powerful pulse. Inspection checks dimensions, coating and magnetic output. The pulse strength is listed in the key figures table on this page.

Why high-temperature grades need heavy rare earths

Heat is the weak point of these magnets. Neodymium magnets have a relatively low Curie temperature, and they start to lose output well before that limit. Adding dysprosium or terbium curbs that loss as the temperature climbs, but those elements cost more and are harder to source. Makers pick a grade family rated for the operating temperature the part will see, then use as little heavy rare earth as the design allows. A diffusion technique lets them push that benefit to the part's surface instead of loading it through the whole body, which cuts the amount of costly material. The grade ladder and temperature ratings are in the key figures table on this page.

Grade letters and maximum operating temperature

Grades run from N28 through N55, with a letter suffix marking the temperature class. Standard grades handle the lowest operating temperature, and the ladder rises through M, H, SH, UH, EH and AH classes. The grade and temperature data from Arnold Magnetic Technologies (opens in a new tab) lists the rated maximum for each class, shown in the key figures table on this page. Choosing a grade is a core design choice in electric vehicle motors, where magnets run hot.

What heavy rare earth additions do

Dysprosium and terbium raise the temperature at which the magnet begins to lose performance. The trade is cost. These heavy elements are scarcer and pricier than the neodymium-praseodymium base. That cost is a central reason buyers of rare earth magnets in electric vehicles watch heavy rare earth supply closely.

Grain boundary diffusion: getting the benefit with less material

Grain boundary diffusion moves heavy rare earth into the magnet along its grain boundaries rather than through the full volume. This cuts dysprosium and terbium use. The method favors thin magnets and laminated materials. The thickness range where it works best is in the key figures table on this page.

Browse rare earth magnet suppliers on the REEx Marketplace (opens in a new tab)

Where are most rare earth magnets made?

Most sintered permanent magnets are made in China, which held the large majority of global output in recent reporting and has grown that share sharply from around half two decades earlier. The concentration runs through the whole chain. China accounts for most mined magnet rare earths and nearly all refined output. Magnets also make up the bulk of rare earth demand when measured by value, far more than their share by weight. Global NdFeB output now runs into the low hundreds of thousands of metric tons per year. The production shares, demand-by-value figure and output estimate are in the key figures table on this page.

Concentration at every stage of the chain

The dominance is not only in finished magnets. Mining and refining are concentrated too, with refining more so than mining. The IEA rare earth summary (opens in a new tab) gives the mining and refining shares, both listed in the key figures table on this page.

Global output and demand by value

Permanent magnets account for most rare earth demand by value, which explains the attention they draw. Annual NdFeB output is measured in metric tons, with the estimate in the key figures table on this page. For a view of how this feeds downstream equipment, see the machines behind the magnets.

New capacity outside the dominant producer

Capacity is starting to appear outside China. One example is an integrated U.S. plant that handles metal, alloy and magnet making under one roof. Its stated annual output and ramp timing are in the key figures table on this page.

Key figures (verified 2026-10-19)

Mining and separation do not produce magnets. They produce oxides. Turning those oxides into metal, then into alloy flake and powder, is where capacity runs thinnest. The IEA names metallisation and magnet manufacturing as the most acute constraints on supply diversification. A new mine or separation plant does not fix that gap. The step short of capacity sits in the middle of the chain, between refined oxide and finished alloy. An integrated plant that runs oxide through electrolysis to metal, then to alloy and sintered magnets, shows what closing that gap takes. Its details are in the key figures table on this page.

Metallization: turning oxide into metal

Oxide must be reduced to metal before any alloy can be cast. This metallization step uses electrolysis cells and is one of the two steps the IEA flags as the main bottleneck.

Alloy flake and powder: the step buyers rarely see

After metal comes alloy. The metal is melted and cast into flake, then processed toward powder. Buyers of finished magnets rarely see this step, yet it is a hard link to secure outside China.

What an integrated mine-to-magnet plant looks like

A mine-to-magnet plant runs the full chain in one place: oxide to metal in electrolysis cells, metal to alloy, and alloy to sintered magnets. One U.S. facility is described as the first fully integrated metal, alloy and magnet operation of its kind. Its stated output and ramp timing are in the key figures table on this page.

Browse rare earth magnet suppliers on the REEx Marketplace (opens in a new tab)

Frequently asked questions

What are neodymium magnets made of?

They are built from an alloy that is mostly iron, with rare earths making up roughly a third by weight and boron close to one percent. The main rare earth input is neodymium-praseodymium, with small additions of cobalt, copper and aluminum. Heavy elements like dysprosium and terbium are added for grades that must run hot. The exact ranges are in the key figures table on this page.

How are rare earth magnets made without casting like regular metal?

Sintered NdFeB magnets are made from powder, not poured as molten metal. Fine alloy powder is pressed in a magnetic field, then fused in a vacuum furnace until the particles bond into a solid body. The parts shrink during firing and are ground to final size afterward.

Why do neodymium magnets lose strength when they get hot?

Neodymium magnets have a relatively low Curie temperature and begin to lose output well before that point. Adding dysprosium or terbium curbs that loss as temperature rises, which is why high-temperature grades carry those heavier elements. The Curie temperature and grade temperature ratings are in the key figures table on this page.

What does the grade number on a neodymium magnet mean?

The number marks the magnet's strength class, running from N28 up to N55. A letter suffix marks the temperature class, rising from standard grades through M, H, SH, UH, EH and AH. A higher number means more magnetic energy; a higher letter class means the magnet can run hotter. Both scales appear in the key figures table on this page.

Where are most neodymium magnets made?

Most sintered permanent magnets are made in China, which holds the large majority of global output and has grown that share sharply over two decades. Mining and refining are concentrated there too, refining even more than mining. New integrated capacity is starting to appear elsewhere. The production and refining shares are in the key figures table on this page.

Why is building a magnet supply chain outside China so hard?

The hardest steps are not mining or separation. They are metallization, which reduces oxide to metal, and the alloy and magnet making that follow. The IEA names these midstream steps as the main bottleneck on supply diversification. Integrated mine-to-magnet projects aim to close that gap.

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