Magnetic Properties of Alnico Magnets Prepared by Hot Pressing

The characteristics of the Alnico 5 and Alnico 8 magnets prepared by hot pressing have been investigated. The raw materials were in the form of powders of the constituent metals. The mixtures of powders were hot compacted in a vacuum using a hot press with inductive heating. The results indicate that the compressibility of Alnico 5 specimens is better than that of Alnico 8 specimens. The theoretical densities for both of Alnico 5 and Alnico 8 were obtained after hot pressing at 800°C for 15 minutes. The optimum magnetic properties of hot pressed magnets are similar to that of commercial sintered Alnico magnets. It is found that the operating point of hot pressed Alnico magnet can affect their temperature coefficient of open circuit magnetic flux. The absolute value of the temperature coefficient of open circuit magnetic flux for hot pressed Alnico 8 magnet increases with increasing the ratio of length/diameter of the magnet. The temperature coefficient of open circuit magnetic flux becomes positive when the B/H is smaller than 2.5. The Alnico 5 is more stable than Alnico 8 and no irreversible losses are greater than 2.7% for Alnico 5 and 3.9% for Alnico 8 after exposure to 550°C. The irreversible losses of Alnico 8 are greater than that of Alnico 5 for short exposure time, however, are smaller than that of Alnico 5 for long term exposure. The SEM fracture surface micrograph of hot deformed Alnico 5 samples does not demonstrate sign of textured characteristics.The characteristics of the Alnico 5 and Alnico 8 magnets prepared by hot pressing have been investigated. The raw materials were in the form of powders of the constituent metals. The mixtures of powders were hot compacted in a vacuum using a hot press with inductive heating. The results indicate that the compressibility of Alnico 5 specimens is better than that of Alnico 8 specimens. The theoretical densities for both of Alnico 5 and Alnico 8 were obtained after hot pressing at 800°C for 15 minutes. The optimum magnetic properties of hot pressed magnets are similar to that of commercial sintered Alnico magnets. It is found that the operating point of hot pressed Alnico magnet can affect their temperature coefficient of open circuit magnetic flux. The absolute value of the temperature coefficient of open circuit magnetic flux for hot pressed Alnico 8 magnet increases with increasing the ratio of length/diameter of the magnet. The temperature coefficient of open circuit magnetic flux becomes positive when the B/H is smaller than 2.5. The Alnico 5 is more stable than Alnico 8 and no irreversible losses are greater than 2.7% for Alnico 5 and 3.9% for Alnico 8 after exposure to 550°C. The irreversible losses of Alnico 8 are greater than that of Alnico 5 for short exposure time, however, are smaller than that of Alnico 5 for long term exposure. The SEM fracture surface micrograph of hot deformed Alnico 5 samples does not demonstrate sign of textured characteristics