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Effect of casting alloy methods on magnetic properties of Sm(CoFeCuZr)z magnet
The 2:17 type SmCo permanent magnets are well known for their excellent magnetic properties, good thermal stability and strong corrosion resistance, which are widely used in high temperature applications 1-2. There are few reports on the preparation of SmCo magnet using strip-casting alloys. In this paper, the effect of casting-alloy methods on the microstructure and magnetic properties of Sm(CoFeCuZr)z magnets was investigated.
The magnetic properties of the PM magnet prepared by mechanical crushing and ball milling are better than those of the SC magnet, especially the orientation. In detail, the magnetic properties of PM magnet are Br=11.63kG, Hcj=25.65kOe, (BH)max=30.97MGOe, while the magnetic properties of the SC magnet are Br=11.45kG, Hcj=24.00kOe, (BH)max=30.03MGOe, respectively. Both random magnets mainly consist of 1:5 and 2:17R phases Fig. 1(a). After oriented, the intensity ratio of (006) and (104) peaks is used to characterize the orientation degree 3, I(006)/I(104)=24.33 in the PM magnet, while this value is 18.23 in the SC magnet. This means that PM magnet has better orientation degree. The EBSD results confirm above result. Meanwhile, there are a few grains with poor orientation in the inverse pole figure Fig. 1(b) of the SC magnet, and such grains will reduce the orientation. Figure 1(c) shows the (0001) pole figure (PF) and inverse pole figure (IPF) of normal direction, from which we can see the MRD values in PF and IPF of PM magnet are both higher than those of SC magnet.
The BSE photographs of the different alloy cross-sections show that the PM alloy consists of columnar grains region, equiaxed grains region Fig. 2a, while the SC alloy consists mainly of columnar grains region and fine grains region. Due to the existence of fine grains region in the SCFig. 2b, it is difficult to obtain all single grain in the subsequent ball-milling process. So the SC magnet has worse orientation than the PM magnet.
References:
1 J.F. Liu, Y. Ding, G. C. Hadjipanayis, J. Appl. Phys., vol.85, p. 2800–2804(1999).
2 Wei Sun, Minggang Zhu, Yikun Fang,. J. Magn. Magn. Mater., vol.378, p. 214-216(2015).
3 Q. J. Zheng, S. Xia, A. Dozier., Mater. Sci. & Tech., vol. 22, p. 1476-1482(2006).
Fig. 1 (a)The XRD patterns of random and oriented magnets, (b) inverse pole figure of magnets, (c)the (0001) pole figure and inverse pole figure of normal direction
Fig. 2 The Cross-sectional BSE of (a) plate ingot alloys and (b) strip-casting alloys.