Presentation Information
[P1-2]Development of Heavy Rare-Earth, Co-free Nd-Fe-B Injection Molded Anisotropic Bonded Magnet with High Corrosion Resistance
*Kazuaki Shimba1, Takumi Otaki1, Masaya Shintaku1, Satoshi Sugimoto2, Hironari Mitarai1 (1. Aichi Steel Corporation (Japan), 2. Department of Management Science and Technology, Graduate School of Engineering, Tohoku University (Japan))
Keywords:
Nd-Fe-B Anisotropic Bonded Magnet,Nd-Fe-B HDDR powder,Corrosion Resistance,Surface treatment of powders,Injection Molding
[Introduction]
An electric water pump (EWP) is an essential component of electric vehicles and is used to cool main functional components. Owing to size reduction requirements, Nd-Fe-B bonded magnets are used in EWP applications [1]. In EWPs, bonded magnet requires long-term durability, which implies low flux loss in hot water. Bonded magnets with high corrosion resistance have been fabricated using phosphoric acid-treated rare-earth powders [2-3]. Additionally, we investigated the phosphoric acid treatment of heavy rare-earth and Co-free anisotropic Nd-Fe-B powders prepared by dynamic hydrogenation disproportionation desorption recombination d-HDDR [4-5] treatment. Phosphoric acid-treated powders baked above 250 °C exhibits high corrosion resistance [6]. In this study, we develop injection-molded magnets with high corrosion resistance by applying oxidation treatment and non-kneading process.
[Experiment]
A base alloy with a composition of Nd12.5FebalGa0.3Nb0.2B6.2 (at. %) was prepared. After d-HDDR treatment and sieving (< 212 μm), raw powders were obtained. Before the phosphoric acid treatment, the raw powders were oxidised in air at 160–180 °C for 3 h. The oxidised powders were treated with phosphoric acid using the method described in the literature [6]. The baking temperature was 300 °C. After sieving (< 212 μm), oxidised and phosphoric acid-treated (referred to as OPAT in short) powders were obtained.
The non-kneading compounds were fabricated as follows: The OPAT powders were coated with 0.5 wt. % amino-silane coupling agents. The treated powders were mixed with 11–14 wt. % polyphenylene-sulfide resin. The mixture was heated at 300 °C and blended using the extruder that was excluded parts adding strong shear stress to powders. Magnets measuring 11×11×11 mm3 were fabricated by heating the compounds at 300 °C and injection molding its, in oriented magnetic field of 1.5 MA/m. The magnet fabricated using the non-kneading process with OPAT powders are called as MA, and raw powders are called as MB. Magnets were also fabricated using compounds prepared by kneading raw powders and resin by a typical process, in which powders were subjected to strong shear stress. This sample is called as MC.
The magnetic properties of the powders were measured at RT by VSM. STEM was employed for microstructural observations. In this study, the corrosion resistance of the powders was evaluated based on the change ratio of the coercivity (ΔHcj) before and after the anticorrosion test. This test was performed by immersing the powders in an aq. solution of 50 % long life coolant (LLC) at 150 °C for 100 h.
The magnetic properties of the magnets were measured using a BH tracer at RT. The irreversible flux loss (ΔFir) of the magnets was calculated based on the surface magnetic-flux density measured using a flux meter after immersion in an aq. of 50 % LLC at 80 °C and cooling to RT.
[Results and discussion]
The ΔHcj value of the OPAT powder was -1.6 %, whereas that of a sample without oxidation treatment was -3.0 %. Based on microstructural observations, an oxidised layer with a thickness of 300–400 nm was fabricated below the phosphate layer. The thickness of the phosphate layer was 100–200 nm and remained unchanged with or without the oxidation treatment. These results indicate that the corrosion resistance of the OPAT powder was improved by the thick multilayers.
Based on the microstructural observations, the powders in MA maintained a multilayer structure. The magnetic properties of MA included a remanence (Br) of 0.73 T and a coercive force (Hcj) of 1060 kA/m. Fig. 1 shows the ΔFir values of the samples after immersion in 80 °C aqueous solution. The ΔFir of the magnet MA was -2.4 % at 8000 h, whereas those of MB and MC were -8 % and -15 % at 1000 h, respectively.
[Conclusion]
The corrosion resistance of the phosphoric acid-treated powder was improved by oxidation treatment. The surface layer of the OPAT powder was maintained after injection molding. In conclusion, Nd-Fe-B anisotropic bonded magnets with high corrosion resistance were obtained, which can be used in applications operating in harsh environments, e.g. EWPs.
[Acknowledgements]
This study was partially supported by a project (JPNP21026) subsidised by the New Energy and Industrial Technology Development Organization (NEDO).
[References]
[1] Hayashi, et al., AISIN Tech. Rev. 20, 64 (2016).
[2] Shigeoka, et. al., JP. Patent No. 5499738 (2014).
[3] S. Tada, et al., INTERMAG Short Papers, 979-8-3503-3836-2 (2023).
[4] Sugimoto, et al., J. Alloys Compd. 330-332, 892 (2002).
[5] Mishima, et al., IEEE Trans. Magn. 37, 2467 (2001).
[6] K. Shimba, et al., IEEE Trans. Magn. 59, 9201104 (2023).
An electric water pump (EWP) is an essential component of electric vehicles and is used to cool main functional components. Owing to size reduction requirements, Nd-Fe-B bonded magnets are used in EWP applications [1]. In EWPs, bonded magnet requires long-term durability, which implies low flux loss in hot water. Bonded magnets with high corrosion resistance have been fabricated using phosphoric acid-treated rare-earth powders [2-3]. Additionally, we investigated the phosphoric acid treatment of heavy rare-earth and Co-free anisotropic Nd-Fe-B powders prepared by dynamic hydrogenation disproportionation desorption recombination d-HDDR [4-5] treatment. Phosphoric acid-treated powders baked above 250 °C exhibits high corrosion resistance [6]. In this study, we develop injection-molded magnets with high corrosion resistance by applying oxidation treatment and non-kneading process.
[Experiment]
A base alloy with a composition of Nd12.5FebalGa0.3Nb0.2B6.2 (at. %) was prepared. After d-HDDR treatment and sieving (< 212 μm), raw powders were obtained. Before the phosphoric acid treatment, the raw powders were oxidised in air at 160–180 °C for 3 h. The oxidised powders were treated with phosphoric acid using the method described in the literature [6]. The baking temperature was 300 °C. After sieving (< 212 μm), oxidised and phosphoric acid-treated (referred to as OPAT in short) powders were obtained.
The non-kneading compounds were fabricated as follows: The OPAT powders were coated with 0.5 wt. % amino-silane coupling agents. The treated powders were mixed with 11–14 wt. % polyphenylene-sulfide resin. The mixture was heated at 300 °C and blended using the extruder that was excluded parts adding strong shear stress to powders. Magnets measuring 11×11×11 mm3 were fabricated by heating the compounds at 300 °C and injection molding its, in oriented magnetic field of 1.5 MA/m. The magnet fabricated using the non-kneading process with OPAT powders are called as MA, and raw powders are called as MB. Magnets were also fabricated using compounds prepared by kneading raw powders and resin by a typical process, in which powders were subjected to strong shear stress. This sample is called as MC.
The magnetic properties of the powders were measured at RT by VSM. STEM was employed for microstructural observations. In this study, the corrosion resistance of the powders was evaluated based on the change ratio of the coercivity (ΔHcj) before and after the anticorrosion test. This test was performed by immersing the powders in an aq. solution of 50 % long life coolant (LLC) at 150 °C for 100 h.
The magnetic properties of the magnets were measured using a BH tracer at RT. The irreversible flux loss (ΔFir) of the magnets was calculated based on the surface magnetic-flux density measured using a flux meter after immersion in an aq. of 50 % LLC at 80 °C and cooling to RT.
[Results and discussion]
The ΔHcj value of the OPAT powder was -1.6 %, whereas that of a sample without oxidation treatment was -3.0 %. Based on microstructural observations, an oxidised layer with a thickness of 300–400 nm was fabricated below the phosphate layer. The thickness of the phosphate layer was 100–200 nm and remained unchanged with or without the oxidation treatment. These results indicate that the corrosion resistance of the OPAT powder was improved by the thick multilayers.
Based on the microstructural observations, the powders in MA maintained a multilayer structure. The magnetic properties of MA included a remanence (Br) of 0.73 T and a coercive force (Hcj) of 1060 kA/m. Fig. 1 shows the ΔFir values of the samples after immersion in 80 °C aqueous solution. The ΔFir of the magnet MA was -2.4 % at 8000 h, whereas those of MB and MC were -8 % and -15 % at 1000 h, respectively.
[Conclusion]
The corrosion resistance of the phosphoric acid-treated powder was improved by oxidation treatment. The surface layer of the OPAT powder was maintained after injection molding. In conclusion, Nd-Fe-B anisotropic bonded magnets with high corrosion resistance were obtained, which can be used in applications operating in harsh environments, e.g. EWPs.
[Acknowledgements]
This study was partially supported by a project (JPNP21026) subsidised by the New Energy and Industrial Technology Development Organization (NEDO).
[References]
[1] Hayashi, et al., AISIN Tech. Rev. 20, 64 (2016).
[2] Shigeoka, et. al., JP. Patent No. 5499738 (2014).
[3] S. Tada, et al., INTERMAG Short Papers, 979-8-3503-3836-2 (2023).
[4] Sugimoto, et al., J. Alloys Compd. 330-332, 892 (2002).
[5] Mishima, et al., IEEE Trans. Magn. 37, 2467 (2001).
[6] K. Shimba, et al., IEEE Trans. Magn. 59, 9201104 (2023).
