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金属学报  2014, Vol. 50 Issue (5): 601-609    DOI: 10.3724/SP.J.1037.2013.00558
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砂型铸造Mg-6Al-xZn合金凝固行为及晶粒尺寸*
侯丹辉1,2, 梁松茂3, 陈荣石2(), 董闯1
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
SOLIDIFICATION BEHAVIOR AND GRAIN SIZE OF SAND CASTING Mg-6Al-xZn ALLOYS
HOU Danhui1,2, LIANG Songmao3, CHEN Rongshi2(), DONG Chuang1
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
引用本文:

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.
Danhui HOU, Songmao LIANG, Rongshi CHEN, Chuang DONG. SOLIDIFICATION BEHAVIOR AND GRAIN SIZE OF SAND CASTING Mg-6Al-xZn ALLOYS[J]. Acta Metall Sin, 2014, 50(5): 601-609.

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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?sDCP; 并讨论了Q 值、晶粒尺寸与?sDCP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    
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)17 phase. 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 (?sDCP). The relationship of values, grain size and ?sDCP has been also discussed.

Key wordsMg-Al-Zn alloy    sand casting    grain size    growth restriction factor    solid fraction at dendrite coherency point
收稿日期: 2013-09-05     
ZTFLH:  TG146.2  
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
Alloy Al Zn Mn Mg
AZ60 5.74 - 0.22 Bal.
AZ62 5.79 1.90 0.21 Bal.
AZ64 5.69 3.70 0.24 Bal.
AZ66 5.82 5.66 0.28 Bal.
表1  合金的化学成分
图1  热分析实验装置图和双电偶热分析确定枝晶相干点示意图
图2  AZ6x合金的热分析结果及对应的铸态显微组织.
图3  热力学计算垂直截面Mg-5.76Al -0.24Mn-xZn四元平衡相图与AZ6x合金的冷却曲线热分析所得的相变温度点对比
Alloy Peak A TDCP Peak B Peak C
Tonset Tpeak Tonset Tpeak Tonset Tpeak
AZ60 617 614 610 439 436 - -
AZ62 610 608 604 407 404 - -
AZ64 602 599 593 389 385 361 359
AZ66 598 594 587 372 369 362 360
表2  从中心电偶热分析曲线中获得的凝固过程中对应的关键温度点(℃)
图4  利用Scheil模型计算以及热分析法得到的AZ6x合金凝固曲线
图5  Mg-6Al-xZn合金的EBSD图
图6  Mg-6Al-xZn合金枝晶相干温度的确定
图7  Zn含量对枝晶相干点固相分数?sDCP的影响
Alloy Average grain size / μm Q fsDCP-Scheil / % fsDCP-TA / %
AZ60 557 21 36 35
AZ62 275 28 27 27
AZ64 271 34 31 26
AZ66 235 43 23 25
表3  AZ6x合金中平均晶粒尺寸、枝晶生长抑制因子( Q 值)和枝晶相干点固相分数?sDCP
图8  不同溶质含量时枝晶形貌模拟图
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