Can an AlNiCo magnet be remagnetized after demagnetization? What equipment is needed?

Yes, AlNiCo magnets can be remagnetized after demagnetization, and the process typically requires specialized equipment such as high-current pulse chargers or capacitive discharge devices.

Remagnetization Mechanism of AlNiCo Magnets

AlNiCo magnets derive their coercivity from the shape anisotropy of precipitates (α1 phase) formed during spinodal decomposition. When subjected to a demagnetizing field or thermal stress, these precipitates may realign, reducing coercivity and magnetic flux density. Remagnetization involves reorienting the magnetic domains to restore the original magnetization state.

Equipment Required for Remagnetization

1. High-Current Pulse Chargers:
   • These devices generate single high-current pulses (up to 15,000 A) to magnetize AlNiCo alloys effectively.
   • The pulse duration is typically 3–5 seconds, ensuring sufficient energy to realign the magnetic domains.
   • Examples include the LIST-MAGNETIK DE-MAG 500 and UKI-MD500, which are designed for both magnetizing and demagnetizing tasks. These devices feature adjustable voltage (50–510 V), programmable logic controller (PLC) control, and compatibility with various coil configurations.
2. Capacitive Discharge Devices:
   • These systems store electrical energy in capacitors and release it instantaneously to create a strong magnetic field.
   • They are suitable for magnetizing AlNiCo magnets in applications requiring precise control over the magnetic field strength and duration.
3. Magnetizing Fixtures:
   • Custom-designed fixtures hold the AlNiCo magnet in place during the remagnetization process.
   • The fixtures are tailored to the magnet's geometry to ensure uniform magnetization and minimize magnetic flux leakage.

Remagnetization Process

1. Preparation:
   • Clean the AlNiCo magnet to remove any contaminants that may interfere with the magnetization process.
   • Position the magnet within the magnetizing fixture, ensuring proper alignment with the coil.
2. Magnetization:
   • Connect the magnetizing fixture to the high-current pulse charger or capacitive discharge device.
   • Set the desired voltage and pulse duration based on the magnet's specifications and the required magnetic field strength.
   • Initiate the magnetization pulse, which generates a strong magnetic field to realign the magnetic domains.
3. Verification:
   • Use a magnetometer or gaussmeter to measure the remagnetized magnet's surface flux density and coercivity.
   • Compare the measured values with the original specifications to ensure the remagnetization process was successful.

Factors Influencing Remagnetization Success

• Magnet Geometry: Magnets with a higher length-to-diameter ratio (L/D) are more resistant to demagnetization and easier to remagnetize due to their inherent shape anisotropy.
• Temperature: Remagnetization should be performed at room temperature or slightly elevated temperatures to enhance domain wall mobility.
• External Fields: Avoid strong demagnetizing fields during the remagnetization process to prevent re-demagnetization.