Novel Fabrication Method for a High-Performance Soft-Magnetic Composite Composed of Alumina-Coated Fe-Based Metal Powder
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https://doi.org/10.1007/s11664-020-08607-8 Ó 2020 The Minerals, Metals & Materials Society
ORIGINAL RESEARCH ARTICLE
Novel Fabrication Method for a High-Performance Soft-Magnetic Composite Composed of Alumina-Coated Fe-Based Metal Powder SUNGJOON CHOI,1 SUNWOO LEE,1 CHRIS YEAJOON BON,1 KANGHYUK LEE,1 SEONG JIN CHOI,2 and SANG-IM YOO1,3 1.—Department of Materials Science and Engineering, Research Institute of Advanced Materials (RIAM), Seoul National University, Seoul 151-744, Republic of Korea. 2.—Chang Sung Co Ltd, R&D Ctr, 11-9 Namdong Ind Area, Inchon 405100, Republic of Korea. 3.—e-mail: [email protected]
A high-performance soft-magnetic composite (SMC) has been successfully fabricated in a toroidal mold without the application of compaction pressure by mixing three different alumina-coated Fe-based metal powders, namely carbonyl iron (FM), Fe-Si-Cr alloy (FSC), and Fe-Si-Al alloy (sendust), with epoxy resin in a centrifugal paste mixer. Surface coating with an alumina layer was performed via a sol–gel process, and its thickness was controlled by varying the coating time. Without the alumina coating, the SMC toroidal core with a FM:FSC:sendust mixing ratio of 8:22:70 by mass exhibited optimal magnetic properties including an effective permeability (leff) of 33.9 and total core loss (Pt) of 252 mW/cm3 at 100 kHz with an amplitude (B) of 50 mT. With the alumina coating, however, the SMC toroidal core with the same mixing ratio exhibited a significantly reduced Pt value of 213 mW/cm3 while its leff value was slightly decreased to 32.4, primarily due to the suppression of the macroscopic eddy-current loss from 115 mW/cm3 to 85 mW/cm3. These results indicate that an optimal mixture of the three different alumina-coated Febased metal powders is very effective for fabricating high-performance SMC cores without external pressure for molding, being applicable for miniature electronic components. Key words: Soft-magnetic composite, insulation coating, magnetic property, eddy-current loss
INTRODUCTION Recently, soft-magnetic composites (SMCs) have attracted much attention due to their excellent magnetic properties such as high saturation magnetization (Ms), low coercivity (Hc), and high effective permeability (leff).1–5 Owing to these properties, SMCs have been widely used in electromagnetic applications, including electromagnetic sensors, power inductors, electromagnetic actuation devices, and low-frequency filters.5–7 However, since Fe-based metal powders have usually been
(Received June 29, 2020; accepted November 3, 2020)
used as soft-magnetic materials for SMCs, the large eddy-current loss at high frequency has been a critical issue for their practical application. Eddycurrent loss not only degrades the device efficiency but also causes Joule heating.4,8–10 An effective method to reduce eddy-current loss is the formation of an insulating coating on the surface of Fe-based metal particles, since interparticle conduction, leading to macroscopic eddy currents, can thereby be effectively suppressed. However, the insu
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