As the isolation coating of silicon steel, magnesium oxide (MgO) not only plays an isolation role, but also significantly improves the processing and magnetic properties of silicon steel through chemical reactions and physical protection. There are mainly the following mechanisms:
1. Isolation effect
Silicon steel sheets will recrystallize and grain growth during high-temperature annealing. If there is no effective isolation layer, adjacent silicon steel sheets will adhere due to the diffusion of metal atoms. The MgO coating plays a physical isolation role, preventing the silicon steel sheet from being bonded together, and improving the stacking coefficient and punching performance of the silicon steel sheet.
2. Reaction to form a vitrified layer
During high-temperature annealing, MgO will react with silica (SiO₂) on the surface of the silicon steel to form a magnesium silicate (Mg₂SiO₄) or magnesium silicate vitrification layer. This vitrified film has good adhesion and stability, which not only enhances the insulation performance, but also improves the oxidation resistance of silicon steel.
3. Improve magnetic performance
MgO coating helps to inhibit the growth of abnormal grains of secondary recrystallization in silicon steel, promote uniform and stable grain growth, thereby improving the magnetic properties of silicon steel (such as reducing iron loss and improving magnetic permeability).
4. Lubrication and protection
During subsequent rolling and punching processing, the MgO coating can reduce friction and wear between the mold and silicon steel, and play a lubricating role. At the same time, it can also protect the surface of silicon steel from mechanical damage.
5. Adjust tension
The vitrified layer will form a certain tension after annealing, which can effectively reduce the hysteresis loss of the silicon steel sheet and further improve the magnetic performance.