Introduction to Permalloy

　　 Fe-Ni alloy is the so-called Permalloy, which is a very important type of soft magnetic material. It shows high permeability and low coercivity under weak magnetic field magnetization, and has good cold working performance. By adjusting the composition (changing the content of Ni, adding one or more alloying elements, such as Mo, Cu, Cr, Ti, etc.) and the process, a variety of permalloys with different characteristics can be obtained. Many, it can be regarded as the most soft magnetic material. However, its disadvantage is that it contains more precious metal Ni. Therefore, the cost is relatively high, and the production equipment is huge, the process is harsh, and the magnetism is greatly affected by the environment. The Fe-Ni alloy produced in my country has all the specifications and brands, and there are already ministerial standards.

Precautions for Permalloy Annealing Process

       Compared with two-stage continuous annealing (950℃×3h→1100℃×3h) and one annealing (1100℃×3h), the coercive force is reduced from 217.6 A/m to 8.8A/m, the coercivity is significantly reduced, and the saturation magnetization The strength increased from 74.22 emu/g to 79.34 emu/g, which was a slight increase. This shows that the use of the two-stage continuous annealing process is beneficial to remove impurities in the alloy and play a role in purifying the alloy, thereby improving the magnetic properties of the alloy.

Permalloy preparation

　　1. The two-stage continuous annealing process is beneficial to remove impurities in the alloy, play a role in purifying the alloy, and at the same time improve the magnetic properties of the alloy, that is, the coercive force is reduced, and the saturation magnetization is increased.

　　2. Extending the holding time is conducive to the growth of alloy crystal grains, reducing defects in the crystal, weakening the pinning effect on the movement of the domain wall, and at the same time, the movement of the domain wall becomes easier, so the magnetic performance is improved. But it is not that the longer the heat preservation time, the better. Because of the long holding time at high temperature, the reduction and oxidation of hydrogen and impurities in the furnace pollute the atmosphere in the furnace, and the hydrogen dew point also rises with the increase of temperature, resulting in a phenomenon that the magnetic properties of the alloy decreases. Therefore, the holding time is extended to 4 hours. On the one hand, it is beneficial to improve production efficiency, and on the other hand, it also obtains better soft magnetic properties. Based on various factors, it is determined that the best heat treatment process for IJ79 alloy is: heating up to 950 ℃ with the furnace, holding for 4 hours, then heating up to 1100 ℃, holding for 4 hours, and finally cooling the furnace to room temperature.

        3. The effect of the change of Ni content in the alloy on its magnetic properties was studied. It is found that the change of Ni content is too small to have a significant effect on the magnetic properties of the alloy. Therefore, during the production process, it is only necessary to ensure that the Ni content is within the composition of the standard issued by the Ministry of Metallurgy (YB129-70).

　　 4. M is added to the alloy. The content is beneficial to increase the saturation magnetic induction intensity and reduce the coercive force. Combining various factors, we found ultra-low H. The preferable composition of the alloy is: Ni 78.00wt%, Mo 5.00wt%, Mn 0.90wt% Si 0.40wt%, Fe balance.