砂型铸造Mg-6Al-xZn合金凝固行为及晶粒尺寸*

侯丹辉; 梁松茂; 陈荣石; 董闯

doi:10.3724/SP.J.1037.2013.00558

金属学报 >

2014 , Vol. 50 >Issue 5: 601 - 609

DOI: https://doi.org/10.3724/SP.J.1037.2013.00558

砂型铸造Mg-6Al-xZn合金凝固行为及晶粒尺寸^*

侯丹辉 ,
梁松茂 ,
陈荣石 ,
董闯

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1 大连理工大学材料科学与工程学院, 大连116024
2 中国科学院金属研究所, 沈阳110016
3 Institute of Metallurgy, Clausthal University of Technology, Clausthal-Zellerfeld, Germany, 38678

收稿日期: 2013-09-05

修回日期: 2013-09-05

网络出版日期: 2014-05-20

基金资助

*国家重点基础研究发展计划项目2013CB632202及国家自然科学基金项目51105350和51301173资助

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SOLIDIFICATION BEHAVIOR AND GRAIN SIZE OF SAND CASTING Mg-6Al-xZn ALLOYS

Danhui HOU ,
Songmao LIANG ,
Rongshi CHEN ,
Chuang DONG

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1 Institute of Material Science and Engineering, Dalian University of Techonlogy, Dalian 116024
2 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016
3 Institute of Metallurgy, Clausthal University of Technology, Clausthal-Zellerfeld, Germany, 38678

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侯丹辉, 男, 1982年生, 博士生

Received date: 2013-09-05

Revised date: 2013-09-05

Online published: 2014-05-20

Supported by

National Basic Research Program of China (No.2013CB632202) and National Natural Science Foundation of China ( Nos.51105350 and 51301173)

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摘要

采用双电偶热分析技术和SEM表征了Mg-6Al-xZn合金(简称AZ6x合金, x=0, 2, 4, 6, 质量分数, %) 在砂型铸造过程中的凝固行为和显微组织; 采用背散射电子衍射(EBSD)分析对合金的晶粒尺寸进行定量表征. 利用Pandat热力学软件计算了合金的平衡截面相图、非平衡Scheil模型凝固过程, 以及枝晶生长抑制因子(growth restriction factor, 或称为 $Q$ 值). 结果表明, 在AZ6x合金的砂型铸造凝固过程中, AZ60合金中只有非平衡凝固的γ-Mg₁₇Al₁₂, 而AZ62~AZ66合金的铸态组织中除了γ-Mg₁₇Al₁₂相, 还出现了Φ-Mg₂₁(Al, Zn)₁₇相, 并且随着Zn含量的增加, γ-Mg₁₇Al₁₂相减少而Φ-Mg₂₁(Al, Zn)₁₇相增多. 热力学计算结果表明, AZ60~AZ64合金中γ-Mg₁₇Al₁₂相和Φ-Mg₂₁(Al,Zn)₁₇相在一定温度下能够完全固溶到α-Mg中, 而AZ66合金中的Φ-Mg₂₁(Al, Zn)₁₇相在任何温度下都不可能完全固溶. 研究结果还表明, Zn含量高的合金具有高的 $Q$ 值、小的晶粒尺寸及低的枝晶相干点固相分数?_s^DCP; 并讨论了 $Q$ 值、晶粒尺寸与?_s^DCP的关系.

关键词： Mg-Al-Zn合金; 砂型铸造; 晶粒尺寸; 枝晶生长抑制因子; 枝晶相干点固相分数

本文引用格式

侯丹辉 , 梁松茂 , 陈荣石 , 董闯 . 砂型铸造Mg-6Al-xZn合金凝固行为及晶粒尺寸^*[J]. 金属学报, 2014 , 50(5) : 601 -609 . DOI: 10.3724/SP.J.1037.2013.00558

Abstract

The solidification behavior and microstructure evolution of sand cast Mg-6Al-xZn alloy (named as AZ6x alloys, x=0, 2, 4, 6, mass fraction, %) were characterized by two-thermocouple thermal analysis technology and SEM. The grain sizes of the alloys were quantitatively determined by EBSD technology. Thermodynamic calculations were applied in Pandat software for phase diagram calculation, Scheil model solidification simulation and growth restriction factor values (GRF or values). The results show that solidification of AZ6x alloys follows non-equilibrium solidification paths. Besides the γ-Mg₁₇Al₁₂ phase, which is the only secondary phase in AZ60 alloy, another Φ-Mg₂₁(Al, Zn)₁₇ phase appears in the as-cast microstructure of AZ62 to AZ66 alloys. With the increase of the Zn content, the amount of γ-Mg₁₇Al₁₂ phase decreases and while increase the amount of Φ-Mg₂₁(Al, Zn)₁₇phase. Calculated equilibrium phase diagram shows that in the AZ60~AZ64 alloys both γ-Mg₁₇Al₁₂ phase and Φ-Mg₂₁(Al, Zn)₁₇ phase can be dissolved into α-Mg under proper heat treatment conditions. However, Φ-Mg₂₁(Al, Zn)₁₇ phase in AZ66 alloy can not be completely dissolved into a-Mg for any temperature. The results also indicate that higher Zn content alloys have higher values and smaller grain size, and lower solid fraction at dendrite coherency point (?_s^DCP). The relationship of values, grain size and ?_s^DCP has been also discussed.

Key words： Mg-Al-Zn alloy; sand casting; grain size; growth restriction factor; solid fraction at dendrite coherency point

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