MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
The Effects of Settling Time on the Quality of Fluxless Mg–Nd–Zn–Zr Melt Preparation
Yanyan HuangChengzhi YangJili ZhaSiyuan LongHanxue Cao
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2019 Volume 60 Issue 6 Pages 1044-1050

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Abstract

The effects of settling time up to 8 h on the quality of fluxless Mg–Nd–Zn–Zr melt preparation are discussed in terms of melt chemistry and inclusions’ structural properties. The content of Nd, Zn and Zr lie in the demanding scope throughout settling process. Neodymium content rises slightly at the settling time of 0.25 h, then decreases gradually up to 8 h. Zinc experiences a slight increase after 0.25 h, then levels off. Zirconium drops sharply at 0.25 h mainly due to the subsidence of undissolved zirconium (Zr) particles, then drops slightly at 1 h, and then stabilizes. The inclusions have various morphologies like rod-like, granular and clustered, and different types such as oxides, carbides, undissolved Zr particles, and etc. The effect of settling time on inclusions’ removal is remarkable during early settling stage, from 0 to 0.25 h, and is getting less stark with increasing time. The area fraction, average diameter and maximum diameter of inclusions all decrease rapidly at 0.25 h, then gradually, and finally reach a plateau region. The changes of minimum diameter and number density values are insignificant through whole process. The theoretical analysis on inclusions’ settling and rising behavior agrees with the experimental data.

Fig. 3 The settling distance as a function of settling time for various inclusions of different sizes, (a) 1 × 10−6, (b) 2 × 10−6, (c) 4 × 10−6, (d) 8 × 10−6, (e) 16 × 10−6 and (f) 32 × 10−6 m, in the melt at 1033 K. The dashed line indicates the sample depth, approximately 0.2 m below the melt surface. Fullsize Image
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© 2019 The Japan Institute of Metals and Materials
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