| ABSTRACT:It is well known that the Fe-6.5wt%alloy has excellent soft magnetic properties for its very low magnetostriction, the magneto-crystalline anisotropy K1just half of the3%Si-Fe alloy and low iron loss. Despite of its excellent properties, Fe-6.5wt%alloy has not been totally industrialized because it is almost impossible to cold-roll by conventional rolling process or machine these alloys into thin strip or sheet due to its brittleness and poor hot workability. And because of its high silicon content(silicon is a kind of anti-magnetic material), the saturation magnetic flux density of Fe-6.5wt%alloy has been greatly reduced, which makes it difficult to satisfy modern electronics requirements such as being portable or having high capacity and performance. Adding Co elements can effectively increase the saturation induction of Fe-6.5wt%Si alloy. In order to overcome these demerits of Fe-6.5wt%alloy, Fe100-xCox-6.5wt%Si (x=0,1,3,5,7,10,15,35,50) alloy powders were produced by inert gas atomization and post-processed to form Fe100-xCox-6.5wt%Si magnetic powder cores. In this study, effects of powder preparation parameters, insulation coating, annealing process and alloys composition on ac/dc magnetic properties of cores were investigated.By superheating the melt100-200℃, the Fe100-xCox-6.5wt%Si ternary alloy powders were successfully manufactured under the pressure of6MPa, the results pointed out that the atomization process was stable. The ingredient of the as-atomized Fe100-xCox-6.5wt%Si powders with low carbon and oxygen contents showed a tiny deviation from the nominal composition, and the spherical powders showed a relatively wide particle size distribution. Besides, there were few satellite balls around the smooth surface of particles. The as-atomized Fe100-xCox-6.5wt%Si powders revealed the presence of only a-Fe phase structure, and the independent characteristic peaks of DO3ordered phase was not observed in XRD diffraction patterns. It was found that adding various Co contents have different effects on the saturation magnetization of Fe-6.5wt%Si, and the Fe9oCo10-6.5wt%Si alloy powder reaches the highest Ms value (Ms= 219.26emu/g). The reason for the highest Ms seems to be that the Boer magnetic moment of single atom reaches the maximum under this composition.The silicone resin(DC-805)coating which utilizes the3-aminopropy ltriethoxy silane(ATPS) as powder surface modification had formed a thin layer around the surface of powder particles. Comparing the magnetic performance of Fe-6.5wt%Si cores with different coating process at f=50kHz, Bm=0.1T, the results showed that the cores performance was better when using the1%ATPS coupling+4%DC-805silicone resin coating procedure.Due to the particle size distribution was not much uniform, there were voids between the particles, so the sample’s green density and densification was relatively low.The coating agent between powder particles gradually reduced with annealing temperature, while no obvious insulation agent "ablation" phenomenon was observed in the cores section, and the insulating layer remained relatively intact. The magnetic properties of Fe100-xCox-6.5wt%Si powder cores presented a nonlinear trends as a function of annealing temperature. Annealing at400～800℃, the cores effective permeability μa of Fe100-xCox-6.5wt%Si (x=l,3,5) powder cores showed a higher value, while the Fe100-xCox-6.5wt%Si powder cores were lower. The coercivity of Fe100-xCox-6.5wt%Si(x=0,1,3,5,7) powder cores were relatively lower and achieved the valley at500℃. Core losses of Fe100-xCox-6.5wt%Si (x=0,1,3,5) cores with annealing temperature fluctuated in small scale were comparatively low.It’s obvious that the powder properties have dramatic effect on the dc performance of cores. By adding appropriate amount of Co, the ac/dc characteristics of cores could be significantly improved. Under the same frequency, Fe95Co5-6.5wt%Si powder cores had the highest effective permeability, while the iron loss was much lower than the Co-free cores. The Fe97Co3-6.5wt%Si powder cores owned the best dc magnetic powder cores, and the saturation magnetization Bs=1.7179T. In general, the Fe95Co5-6.5wt%Si powder cores possessed excellent comprehensive magnetic properties. |
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