Growth crystallography and in-situ imaging of nucleation and growth dynamics of Al8Mn5 solidifying in AZ magnesium alloys

IF 8.3 1区 材料科学 Q1 MATERIALS SCIENCE, MULTIDISCIPLINARY
D. Wang, G. Zeng, J.W. Xian, K. Nogita, H. Yasuda, C.M. Gourlay
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Abstract

Many magnesium-aluminium-based alloys contain a small manganese addition to improve corrosion resistance. However, this introduces Al-Mn intermetallics which add complexity to the phase transformations. Here we study the crystal growth of the most common Al-Mn phase, Al8Mn5, in Mg-Al-Zn-Mn-based magnesium alloy solidification by combining electron microscopy of the faceted growth crystallography with in-situ synchrotron X-ray imaging of the Al8Mn5 nucleation and growth dynamics. Three Al8Mn5 morphologies, equiaxed, rod and plate, are shown to all come from cyclic twinned growth associated with the pseudo-cubic symmetry of rhombohedral Al8Mn5. X-ray imaging revealed Al8Mn5 nucleated throughout the freezing range and grew with α-Mg dendrites over a wide temperature range by divorced eutectic solidification. This occurs because, in these alloys, Mn solute has little influence on the solute undercooling of growing α-Mg dendrites, although strongly affects the constitutional supercooling with respect to the Al8Mn5 liquidus. Rod/plate growth of Al8Mn5 is shown to be promoted by slow cooling rates and by divorced eutectic solidification. The findings provide new insights into the conditions that cause large, deleterious rods and plates, and explain why there is a large variation in Al8Mn5 growth morphology after solidification.

Abstract Image

Al8Mn5在AZ镁合金中凝固成核和生长动力学的生长晶体学和原位成像
许多镁铝基合金含有少量锰以提高耐腐蚀性。然而,这引入了Al-Mn金属间化合物,增加了相变的复杂性。本文采用电子显微镜的多面生长晶体学和原位同步加速器x射线成像技术研究了mg - al - zn - mn基镁合金凝固过程中最常见的Al-Mn相Al8Mn5的晶体生长过程。Al8Mn5的三种形态(等轴、棒状和板状)均来自于与Al8Mn5菱形体拟立方对称相关的循环孪晶生长。x射线成像显示Al8Mn5在整个凝固范围内均成核,并在较宽的温度范围内随α-Mg枝晶生长。这是因为,在这些合金中,Mn溶质对生长的α-Mg枝晶的溶质过冷影响很小,但对Al8Mn5液相的本构过冷影响很大。缓慢冷却速率和分离共晶凝固促进了Al8Mn5棒材/板材的生长。这一发现为研究造成大而有害的棒材和板材的条件提供了新的见解,并解释了Al8Mn5凝固后生长形态发生巨大变化的原因。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Acta Materialia
Acta Materialia 工程技术-材料科学:综合
CiteScore
16.10
自引率
8.50%
发文量
801
审稿时长
53 days
期刊介绍: Acta Materialia serves as a platform for publishing full-length, original papers and commissioned overviews that contribute to a profound understanding of the correlation between the processing, structure, and properties of inorganic materials. The journal seeks papers with high impact potential or those that significantly propel the field forward. The scope includes the atomic and molecular arrangements, chemical and electronic structures, and microstructure of materials, focusing on their mechanical or functional behavior across all length scales, including nanostructures.
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