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金属学报  2019, Vol. 55 Issue (3): 389-398    DOI: 10.11900/0412.1961.2018.00399
  本期目录 | 过刊浏览 |
Er对Mg-5Zn-xEr镁合金热裂敏感性的影响
刘耀鸿,王朝辉(),刘轲,李淑波,杜文博
北京工业大学材料科学与工程学院 北京 100124
Effects of Er on Hot Cracking Susceptibility of Mg-5Zn-xEr Magnesium Alloys
Yaohong LIU,Zhaohui WANG(),Ke LIU,Shubo LI,Wenbo DU
College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124, China
全文: PDF(11584 KB)   HTML
摘要: 

采用优化的RDG (Rappaz-Drezet-Gremaud)热裂模型预测了Mg-5Zn-xEr (x=0.83、1.25、2.5、5,质量分数,%)三元多相合金的铸造热裂敏感性,并利用“约束杆”钢模铸造(CRC)实验评价了该合金的热裂敏感性。结果表明,优化的RDG热裂模型可准确地预测Mg-5Zn-xEr镁合金的热裂敏感性:随着Er含量的增加,合金的热裂敏感性呈先增加后降低的趋势,当Er含量为2.5%时合金的热裂敏感性最高,当Er含量为5.0%时合金的热裂敏感性最低,与实验结果相一致。对铸件凝固曲线、相组成、微观组织等进一步分析表明,当Er含量提高至2.5%时,合金凝固过程发生包晶反应生成I相的同时消耗了液相,并且扩大了合金的凝固温度区间,使合金的热裂敏感性上升;Er含量继续提高至5.0%时,合金在凝固过程中发生L→α-Mg+W的共晶反应,凝固温度区间减小,有利于凝固后期枝晶间裂纹的补缩,显著降低了合金的热裂敏感性。

关键词 RDG模型Mg-Zn-Er合金热裂敏感性微观组织    
Abstract

Mg-Zn-Er casting magnesium alloys have good properties, such as high specific strength, high specific stiffness and remarkable temperature creep properties. Current researches mainly focused on the phases and mechanical properties at room and high temperatures. However, the effect of Er on hot cracking susceptibility of Mg-5Zn-xEr magnesium alloys was barely studied. In this work, a modified RDG (Rappaz-Drezet-Gremaud) model for predicting the hot cracking susceptibility of Mg-5Zn-xEr (x=0.83, 1.25, 2.5, 5, mass fraction, %) ternary alloys was proposed, which considered the effects of phase and solidification temperature range on the hot cracking susceptibility of the multiphase alloys. And, the hot cracking susceptibility was evaluated by the experiment of constrained rod casting (CRC). The results indicated that the modified RDG model could accurately predict the hot cracking susceptibility of Mg-5Zn-xEr magnesium alloys. The hot cracking susceptibility increased with the addition of Er up to 2.5%, and Mg-5Zn-2.5Er alloy showed the maximal hot cracking susceptibility; when the addition of Er increased to 5.0%, Mg-5Zn-5Er alloy exhibited the minimal hot cracking susceptibility. The calculated results were consistent with the experimental ones. Further analysis on the casting solidification curves, phases and microstructures showed that I-phase precipitated by peritectic reaction during solidification of Mg-5Zn-2.5Er alloy depleted liquid phases and extended the solidification temperature range of the alloy, leading to the hot cracking susceptibility increasing. The Mg-5Zn-5Er alloy underwent eutectic reaction of L→α-Mg+W during solidification, which reduced the solidification temperature range. Meanwhile, this process was beneficial to feeding the interdendritic hot cracking in the terminal period of solidification, which significantly decreased the hot cracking susceptibility of Mg-5Zn-5Er alloy.

Key wordsRDG model    Mg-Zn-Er alloy    hot cracking susceptibility    microstructure
收稿日期: 2018-08-30      出版日期: 2018-12-17
ZTFLH:  TG146  
基金资助:国家重点研发计划项目(2016YFB0301001);北京市自然科学基金项目(2162003)
通讯作者: 王朝辉     E-mail: wangzhaohui@bjut.edu.cn
Corresponding author: Zhaohui WANG     E-mail: wangzhaohui@bjut.edu.cn
作者简介: 刘耀鸿,男,1993年生,硕士生

引用本文:

刘耀鸿,王朝辉,刘轲,李淑波,杜文博. Er对Mg-5Zn-xEr镁合金热裂敏感性的影响[J]. 金属学报, 2019, 55(3): 389-398.
Yaohong LIU,Zhaohui WANG,Ke LIU,Shubo LI,Wenbo DU. Effects of Er on Hot Cracking Susceptibility of Mg-5Zn-xEr Magnesium Alloys. Acta Metall Sin, 2019, 55(3): 389-398.

链接本文:

http://www.ams.org.cn/CN/10.11900/0412.1961.2018.00399      或      http://www.ams.org.cn/CN/Y2019/V55/I3/389

Alloy (Zn/Er ratio)ZnErMg
Mg-5Zn-0.83Er (6)5.310.71Bal.
Mg-5Zn-1.25Er (4)5.311.19Bal.
Mg-5Zn-2.5Er (2)5.322.36Bal.
Mg-5Zn-5Er (1)5.455.31Bal.
表1  Mg-5Zn-xEr合金的成分
图1  热裂敏感性影响系数示意图
图2  热裂敏感性实验装置示意图
图3  Mg-5Zn-xEr合金的固相体积分数(fs)与凝固温度(T)关系曲线
AlloyFitting function expressionR2

Mg-5Zn-0.83Er

Mg-5Zn-1.25Er

Mg-5Zn-2.5Er

Mg-5Zn-5Er

fs(T)=0.98886-3.854×10-12exp (0.042T)

fs(T)=0.971-3.09×10-9exp (0.031T)

fs(T)=0.9779-5.687×10-16exp (0.056T)

fs(T)=1.00089-9.178×10-10exp (0.033T)

0.987

0.969

0.991

0.978

表2  Mg-5Zn-xEr合金的fs-T拟合函数表达式及其相关系数(R2)
图4  Mg-5Zn-xEr合金热裂敏感性预测
图5  Mg-5Zn-xEr合金热裂敏感性试样及评价结果(临界尺寸法实验)
图6  Mg-5Zn-xEr合金的XRD谱
图7  Mg-5Zn-xEr合金的SEM像及EDS谱
图8  Mg-5Zn-xEr合金的凝固曲线(临界尺寸法实验)
Alloyα-MgW-phaseI-phaseΔT
Mg-5Zn-0.83Er616.4-438.7177.7
Mg-5Zn-1.25Er613.7566.6425.1188.6
Mg-5Zn-2.5Er615.3544.9419.8195.5
Mg-5Zn-5Er593.4532.1-61.3
表3  Mg-5Zn-xEr合金的各相析出温度和凝固区间范围(临界尺寸法实验)
图9  Mg-5Zn-xEr合金热裂断口形貌(纵截面)
图10  Mg-5Zn-xEr合金热裂断口形貌(俯视图)
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