In situ synchrotron tomographic investigation of the solidification of an AlMg4.7Si8 alloy

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• 作者：D. Tolnai^a ; ^b ; ^{domonkos.tolnai@hzg.de} ; P. Townsend^a ; ¹ ; G. Requena^a ; L. Salvo^c ; J. Lendvai^b ; H.P. Degischer^a
• 关键词：In situ ; Eutectic solidification ; Synchrotron radiation computed tomography ; 3-D characterization ; Cast Al&ndash ; Mg&ndash ; Si alloys
• 刊名：Acta Materialia
• 出版年：2012
• 期刊代码：1_13596454
• 类别：ms
• 出版时间：April, 2012
• 卷：60
• 期：6-7
• 页码：2568-2577
• 文件大小：2675 K

摘要

The solidification sequence of an AlMg4.7Si8 alloy is imaged in situ by synchrotron microtomography. Tomograms with (1.4 渭m)³/voxel have been recorded every minute while cooling the melt from 600 掳C at a cooling rate of 5 K min^鈭? to 540 掳C in the solid state. The solidification process starts with the three-dimensional evolution of the 伪-Al dendritic structure at 590 掳C. The growth of the 伪-Al dendrites is described by curvature parameters that represent the coarsening quantitatively, and ends in droplet-like shapes of the secondary dendrite arms at 577 掳C. There, the eutectic valley of 伪-Al/Mg₂Si is reached, forming initially octahedral Mg₂Si particles preferentially at the bases of the secondary dendrite arms. The eutectic grows with seaweed-like Mg₂Si structures, with increasing connectivity. During this solidification stage Fe-aluminides form and expand as thin objects within the interdendritic liquid. Finally, the remaining liquid freezes as ternary 伪-Al/Mg₂Si/Si eutectic at 558 掳C, increasing further the connectivity of the intermetallic phases. The frozen alloy consists of four phases exhibiting morphologies characteristic of their mode of solidification: 伪-Al dendrites, eutectic 伪-Al/Mg₂Si 鈥淐hinese script鈥?with Fe-aluminides, and interpenetrating 伪-Al/Mg₂Si/Si ternary eutectic.