熱壓與熱變形製程對NdFeB永久磁石磁特性及微觀組織之相關性研究

本研究以NdFeB MQU-F磁粉自製成MQ2磁石，再將其熱變形成MQ3磁石，探討不同熱壓及熱變形製程對MQ3磁石微觀組織及磁性之影響。第一部分探討熱變形壓縮率、溫度及應變速率的效應影響。利用掃描式電子顯微鏡(SEM)以及X光繞射儀(XRD)觀察晶粒微觀結構和(00L)配向度，並解釋磁特性、配向度以及晶粒形貌三者間之關係。結果顯示由MQU-F所製之MQ3磁石，其最佳製程條件為壓縮率為70 %，且在溫度780 oC下壓製240 s (應變速率為5*10-3 s-1)，磁石磁特性可達Br = 13.4 kG、iHc = 15.5 kOe、(BH)max = 45.1MGOe、iHc+(BH)max = 60.6。第二部分探討MQ3磁石上到下之整體均勻性，將磁石分為未研磨拋光及上下各研磨拋光12.5%厚度後觀察磁特性差異。結果顯示研磨前後磁特性差異最小的MQ3磁石為壓縮率70 %、溫度780 oC下壓製240 s (strain rate為5*10-3 s-1) ，並藉由晶粒形貌的變化和磁石整體配向度的變化來證實MQ3磁石整體均勻性與壓製時間的長短有關係。第三部分探討不同密度之MQ2磁石其均勻性以及晶粒大小及其對最終製成MQ3磁石磁性之影響。發現MQ2磁石密度越大，晶粒越小整體均勻性也越好。其中以密度7.58cm3/g之MQ2磁石晶粒最小(70 nm) 。利用密度7.58cm3/g之MQ2磁石所壓製的MQ3磁石在任何製程下皆比密度7.5cm3/g之MQ2磁石所壓製的MQ3磁石有更好的磁特性，也有更優越的磁晶配向度。該MQ3磁石上下表面各經研磨約12.5%厚度後之磁性可達本研究之最佳值，其Br = 14.4 kG、iHc = 15.8 kOe、(BH)max = 51.5 MGOe，而iHc+(BH)max = 67.3。

關鍵字

熱變形釹鐵硼磁石

並列摘要

In this study, commercial isotropic NdFeB powders, MQU-F, were adopted to make isotropic MQ2 magnets followed by hot deformation process to prepare anisotropic MQ3 magnets. Firstly, the effects of height reduction, deformation temperature and strain rate on the microstructure and magnetic properties of hot-deformed MQ3 magnets were discussed. The intensity ratio of I(006)/I(105) was evaluated from XRD analysis and the grain morphologies were observed by SEM to correlate with the magnetic performance of the MQ3 magnets. Among all samples, the optimal magnetic properties of Br = 13.4 kG、iHc = 15.5 kOe、(BH)max = 45.1MGOe、iHc+(BH)max = 60.6 was obtained in the magnet for 70 % height reduction and hot pressing at 780 oC for 240 s (strain rate 5*10-3 s-1). Secondly, the results show that with the decrease of strain rate, the uniformity of magnetic properties of the magnets was improved. Thirdly, with increasing the density of MQ2 magnets, the grain size could be decreased. The smallest grain size of ~70 nm was obtained for MQ2 magnet with the density of 7.58 g/cm3. In addition, the (00L) texture and magnetic properties of MQ3 magnet, which made from above high density MQ2, were enhanced effectively. The optimal magnetic properties of Br = 14.4 kG, iHc = 15.8 kOe, (BH)max = 51.5 MGOe, and iHc+(BH)max = 67.3 was obtained (70 % reduction, hot pressing at 780 oC for 120 s (strain rate 9.9*10-3 s-1)), if 12.5% thickness in both sides of the magnet was polished.

並列關鍵字

Hot deformation Nd-Fe-B magnet

參考文獻

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熱壓與熱變形製程對NdFeB永久磁石磁特性及微觀組織之相關性研究

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