Mechanisms of grain refinement by intensive shearing of AZ91 alloy melt
Mechanisms of grain refinement by intensive shearing of AZ91 alloy melt
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DOI：
10.1016/j.actamat.2010.08.016
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发表时间：
2010-11-01
期刊：
影响因子：
9.4
通讯作者：
Fan, Z.
中科院分区：
文献类型：
--
作者：
Men, H.;Jiang, B.;Fan, Z.
最近已经证明，强烈的熔体剪切对于镁合金的压铸和连铸的晶粒细化来说是一种有效的方法。在本研究中，通过建模和实验相结合的方法研究了强烈熔体剪切细化晶粒的机制。对经过和未经过强烈熔体剪切的AZ91合金进行了凝固过程中冷却曲线的测量、凝固样品晶粒尺寸的量化以及加压过滤样品中氧化镁颗粒尺寸和尺寸分布的图像分析。然后将实验结果用作自由生长模型的输入参数，以研究强烈熔体剪切细化晶粒的机制。实验结果表明，尽管强烈熔体剪切不会改变形核起始温度，但它会提高形核结束温度，从而导致形核过冷度降低。使用自由生长模型进行的理论建模定量地揭示，强烈熔体剪切能够有效地将氧化膜中密集分布的氧化镁颗粒分散为合金熔体中更多的单个颗粒，使得氧化镁颗粒密度与未剪切熔体相比增加了三个数量级，活性形核氧化镁颗粒的密度增加了20倍。因此，可以有把握地将强烈熔体剪切的晶粒细化效果归因于合金熔体中作为有效形核位点的天然氧化镁颗粒的细化效率显著提高。（C）2010 Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
It has been demonstrated recently that intensive melt shearing can be an effective approach to the grain refinement of both shape casting and continuous casting of Mg alloys. In the present study, the mechanisms of grain refinement by intensive melt shearing were investigated through a combination of both modelling and experimental approaches. The measurement of the cooling curves during solidification, quantification of grain size of the solidified samples, and image analysis of the MgO particle size and size distribution in the pressurized filtration samples were performed for the AZ91 alloy with and without intensive melt shearing. The experimental results were then used as input parameters for the free growth model to investigate the mechanisms of grain refinement by intensive melt shearing. The experimental results showed that, although intensive melt shearing does not change the nucleation starting temperature, it increases the nucleation finishing temperature, giving rise to a reduced nucleation undercooling. The theoretical modelling using the free growth model revealed quantitatively that intensive melt shearing can effectively disperse MgO particles densely populated in the oxide films into more individual particles in the alloy melt, resulting in an increase in the MgO particle density by three orders of magnitude and the density of active nucleating MgO particles by a factor of 20 compared with those of the non-sheared melt. Therefore, the grain refining effect of intensive melt shearing can be confidently attributed to the significantly increased refining efficiency of the naturally occurring MgO particles in the alloy melt as potent nucleation sites. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.