Study On The Preparation And Properties Of Sr-ferrite Magnetic Composite Materials

Permanent magnet materials are widely used as functional materials in modern industry.Resin bonded magnetic composites have been used in various aspects of production and life because of its unique processability.Coupling agents make an important impact in improving the overall performance of the bonded magnets.Compared with other molding methods,mold-pressing process can achieve higher magnetic powder filling rate of bonded magnet.Making bonded magnet superior in magnetic and mechanical properties.In this paper,nylon 6/Sr-ferrite magnetic composites were prepared by extrusion granulation-molding method.Nylon 6/phenolic resin/Sr-ferrite magnetic composites were prepared by cold pressing thermosetting method.The properties of bonded magnet were investigated by means of scanning electron microscope?SEM?,melt mass flow rate?MFR?and polarized light microscopy.Tested the type and content of coupling agent?silane coupling agent KH550,titanate coupling agent TMC311,and zircoaluminate coupling agent LD139?on the properties and microstructure of nylon 6/Sr-ferrite when the magnetic powders filling rate is85wt%.Finally,a more suitable amount of the coupling agents used for 90 wt%Sr-ferrite content was selected to verify the effect of 85 wt%Sr-ferrite content with the same preparation process.At last,the effect of the addition of nylon 6 to phenolic resin on the magnetic and mechanical properties was explored.Achived results as follows:?1?When the filling rate of magnetic powders was 85wt%.Magnetic powders modified by the KH550 with the amount of KH550 was 1.7wt%made nylon 6/Sr-ferrite form a very good interface and obtain the highest mechanical properties.The maximum compression strength?R_c?is 220.8 MPa,higher than the maximum values of155.4 and 146.4 MPa when TMC311 and LD139 were added.TMC311 used to coupled nylon 6 and Sr-ferrite can make magnetic composites have better integrated magnetic properties.Achieyed B_r=151.1mT,H_cj=212.8 kA·m^-1,?BH?_m=4.09 kJ·m^-33 when the amount of TMC311 was 1.5wt%of magnetic powders.But the interface between the magnetic powders and nylon 6 was weak,and the R_c was further down as the addition of TMC311 was improved.Moreover,the addition of LD139 leads to the bonded magnets reaching the highest melt mass-flow rate and then results in highest H_cj(228.0 kA·m^-1)when the LD139 was 1.7 wt.%of Sr-ferrite powders.?2?The filling rate of magnetic powders was increased from 85 wt%to 90 wt%.Coupling agents made the same law to nylon 6/Sr-ferrite.Meanwhile,H_cjj and the magnet orientation cos?was decreased,but R_c,B_r,?BH?_mwas increased.Nylon 6/Sr-ferrite got the highest R_c?229.7MPa?when KH550 was 1.5wt%of Sr-ferrite.When TMC311 was 1.5wt%of Sr-ferrite,B_r=163.2 mT,H_cj=169.3kA·m^-1,?BH?_m=4.58kJ·m^-3.When the LD139 was 1.7wt%of Sr-ferrite,the maximum H_cj(201.7 kA·m^-1)was obtained.The binder content of 10wt%was suitable for the filling gap of the selected magnetic powders.?3?The occurrence of the interaction between nylon 6 and phenolic resin changed the chains segments of resins to increase the compressive strength.The compressive strength can reach 233.0 MPa when the amount of nylon 6 was 15wt%of phenolic resin,which was 33.44%higher than that without PA6.However,further increase in the addition of nylon 6,decrease in R_c was occured.The magnetic properties was hardly changed as the improve of nylon 6.The main reason is that the appropriate amount of nylon 6 was wrapped in phenolic resin when curing process of phenolic resin.which plays a role as a flexible curing agent to increase the R_c.