Abstract: Using 0.5 mm-thick 3.5% Si（mass fraction） silicon steel as the model material,MgO and MgO-Al₂O₃composite insulating coatings have been applied to the specimen surface after decarburization in a CO₂-CO atmosphere.Through oxide-layer insulation modification,the effects of coating composition on the surface oxide morphology,microstructure,and magnetic properties of the silicon steel have been systematically investigated.The results indicate that,after MgO modification,a Mg₂SiO₄ glassy insulating underlayer forms on the surface of the silicon steel,while the overall oxide-layer thickness remains essentially unchanged.Furthermore,the introduction of Al₂O₃ significantly reduces the carbon content within the silicon steel strip.With increasing Al₂O₃ content in the composite coating,the resulting magnesium silicate（Mg₂SiO₄） glass layer becomes progressively denser and more uniform.The reaction between MgO and the substrate oxide layer is enhanced,while the interaction between Al₂O₃ and Mg₂SiO₄ does not compromise the overall compactness of the oxide layer.Magnetic property measurements show that when the Al₂O₃ content in the composite coating is 2%,the magnetic induction B₅₀ reaches 1.917 T,while the core loss P_1.5/50 decreases to as low as2.113 W/kg.With further increases in Al₂O₃ content,the magnetic induction of the samples gradually declines,accompanied by a corresponding increase in core loss.