Improved Microstructural and Mechanical Properties Inhomogeneity of a Large-Scale AZ91D Magnesium Alloy Billet by Low-Frequency Electromagnetic Casting

IF 3.3 3区材料科学 Q2 MATERIALS SCIENCE, MULTIDISCIPLINARY

Metals and Materials International Pub Date : 2024-10-22 DOI:10.1007/s12540-024-01823-5

Biaobiao Liu, Lei Song, Hongxia Wang, Jian Wang, Quanfu Zhang, Naidong Ren, Lifei Wang, Weili Cheng, Hua Hou, Kwang Seon Shin

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Abstract

The effects of low-frequency electromagnetic field on the homogeneity of microstructure and mechanical properties of Φ530 mm AZ91D magnesium alloy were investigated. Given the Lorentz force, velocity variations and temperature distribution under different electromagnetic conditions, the grain refinement mechanism and improving microstructure uniformity by low-frequency electromagnetic field were discussed in detail. Results show that the grain sizes decreased from 224.91–355.29 μm (direct-chill (DC) casting) to 203.91–235.56 μm at the frequency of 17 Hz, and the thick dendrites disappeared. The low-frequency electromagnetic field can increase the nucleation driving force of α-Mg and reduce the critical nucleus radius, thereby enhancing the nucleation rate. Additionally, forced convection could reintroduce fractured dendrites into the melt, thereby promoting heterogeneous nucleation. The precipitation of the β-Mg₁₇Al₁₂ was promoted as a result of the low-frequency electromagnetic field accelerating the cooling rate of the melt. Al³⁺ moved in a helical trajectory towards the edge of the ingot under the influence of the magnetic field, resulting in a significantly higher content of the β-Mg₁₇Al₁₂ at R/2 and the edge of the ingot. In addition, the application of a low-frequency electromagnetic field enhanced the mechanical properties of the alloy while diminishing the performance disparity between different regions of the casting.

Graphical Abstract

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低频电磁铸造改善AZ91D镁合金方坯组织和力学性能的不均匀性

研究了低频电磁场对Φ530 mm AZ91D镁合金组织均匀性和力学性能的影响。考虑不同电磁条件下的洛伦兹力、速度变化和温度分布，详细讨论了低频电磁场细化晶粒的机理和提高组织均匀性的方法。结果表明：在17 Hz频率下，直接冷铸的晶粒尺寸从224.91 ~ 355.29 μm减小到203.91 ~ 235.56 μm，粗枝晶消失；低频电磁场可以增大α-Mg的成核驱动力，降低临界核半径，从而提高成核速率。此外，强制对流可以将断裂的枝晶重新引入熔体，从而促进非均质成核。低频电磁场加速了熔体的冷却速度，促进了β-Mg17Al12的析出。在磁场的影响下，Al3+沿螺旋轨迹向铸锭边缘移动，导致R/2和铸锭边缘处β-Mg17Al12含量显著升高。此外，低频电磁场的应用提高了合金的力学性能，同时减小了铸件不同区域之间的性能差异。图形抽象

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来源期刊

Metals and Materials International 工程技术-材料科学：综合

CiteScore

7.10

自引率

8.60%

发文量

197

审稿时长

3.7 months

期刊介绍： Metals and Materials International publishes original papers and occasional critical reviews on all aspects of research and technology in materials engineering: physical metallurgy, materials science, and processing of metals and other materials. Emphasis is placed on those aspects of the science of materials that are concerned with the relationships among the processing, structure and properties (mechanical, chemical, electrical, electrochemical, magnetic and optical) of materials. Aspects of processing include the melting, casting, and fabrication with the thermodynamics, kinetics and modeling.