| Magnetic powder core material,also known as soft magnetic composites(SMCs)are widely employed in various electron components,such as inductor.With the rapid development of mobile communication,intelligent manufacturing,automotive electronics,electronic new energy and other emerging fields,reducing the magnetic loss and improving other properties of SMCs are required.In this work,aiming at developing the SMCs for surface mounted devices(SMD)with low cost and high magnetic properties,different insulation coating agents were employed as multiple coating layers,and different insulating treatments were investigated.The frequency stability has been enhanced and the magnetic loss has been reduced by forming continuous and uniform insulating layers on the surface of magnetic powders to insulate and protect the particles.The underlying physical mechanism of magnetic loss reduction is clarified based on the study on the microstructure improvement after insulating coating and the magnetic loss separation.In addition,the effects of insulation coating treatment on the mechanical properties and electrical insulation properties have been also investigated.The main research contents and results are as follows:Firstly,the effects of pretreatment of carbonyl iron powders on the magnetic properties of SMCs were studied.After phosphating or silane coupling treatment,the frequency stability of SMCs was significantly improved,and its permeability could remain stable up to 1MHz.Based on the phosphating process investigation,the SMCs by simplified phosphating with 0.7 wt.%phosphate acid have the lowest magnetic loss and high permeability.The results of the magnetic loss separation show that,after phosphating treatment,the hysteresis loss of the SMCs accounts for 21.1%of its total loss at 200 k Hz.The phosphate layers were formed on particles surfaces after phosphating treatment and silane layers were formed after silane coupling treatment.Secondly,the organic resin coating was carried out on the magnetic powders after pretreatment,and the effects of different pretreatment processes on resin coating were studied.It is demonstrated that the silane coupling treatment can improve adhesion and compatibility between the magnetic powders and coated resin,and the phosphating treatment gives rise to SMCs with high electrical insulation and low magnetic loss.The phosphating treatment is more suitable for industrial production than coupling treatment because of its simplification and effectivity.It is found that coating with 3.0 wt.%mixed resin can bring SMCs with excellent electrical insulation performance and mechanical properties.Its resistance rate is up to 2.23×10~7??m.Finally,the influences of mixed resin composition on SMCs properties were studied.The optimal mass ratio of high temperature epoxy resin to silicone resin is found to be 1:5?1:2.After coating with mixed resin with this composition,the energy efficiency and temperature stability of the magnets were improved significantly.The magnetic loss of SMCs coated with the mixed resin is dominated by hysteresis loss,and the eddy current loss accounts for only16.61%of the total loss at 600 k Hz,indicating that the inter-particle eddy current is effectively eliminated after double-layer coating.Below 125?,increasing the application temperature can significantly reduce the energy loss,which means that the material has a feedback effect on magnetic loss and heat generation.Based on the above results,the quality factor of SMCs has been successfully enhanced by multiple-layer coating.The effect of insulating layers on magnetic loss has also been analyzed by experiments and theories.This work can provide good guidance for preparing the SMCs with high performance and low cost. |
PDF Full Text Request