Transactions of Nonferrous Metals Society of China The Chinese Journal of Nonferrous Metals

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中国有色金属学报

ZHONGGUO YOUSEJINSHU XUEBAO

第18卷    第1期    总第106期    2008年1月

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文章编号:1004-0609(2008)01-0118-08
Sb、Bi合金化提高Mg-Al系合金抗蠕变性能的机理
周惦武1,刘金水2,卢远志1,张楚惠1

((1. 湖南大学 汽车车身先进设计制造国家重点实验室,长沙 410082;2. 湖南大学 材料科学与工程学院,长沙 410082))

摘 要: 采用基于密度泛函理论的Dmol 4.1程序,从合金形成热、结合能、热力学性能和态密度等方面,研究SbBi合金化提高Mg-Al系合金抗蠕变性能的影响机理。结果表明:SbBi分别置换Mg-Al系合金Mg17Al12相中Mg(Ⅰ)Mg()Mg()Al原子时,仅Sb置换Mg17Al12相中Mg(Ⅰ)Mg(Ⅱ) 原子,Bi置换Mg17Al12相中Mg(Ⅰ)原子能形成稳定的Mg17Al12固溶体结构,这表明SbBiMg17Al12中固溶量有限。进一步比较合金化形成稳定的固溶体结构,发现SbBi合金化后,固溶体结构的稳定性比未合金化时增强,其中,Sb置换Mg17Al12相中Mg(Ⅱ)原子时,其结构稳定性最高,其次Sb置换Mg17Al12相中Mg(Ⅰ)原子,再次Bi置换Mg17Al12相中Mg(Ⅰ)原子;而析出金属间化合物Mg3Bi2Mg3Sb2,比相应合金化Mg17Al12固溶体的结构更稳定。不同温度下热力学性能的计算发现,合金体系中形成了结构稳定性高的SbBi合金化Mg17Al12固溶体以及金属间化合物Mg3Sb2Mg3Bi2,这些相高的结构稳定性并不因温度的升高而消失,其结构稳定性仍比Mg17Al12相高,因此SbBi合金化提高了Mg-Al系合金的抗蠕变性能。电子态密度的分析结果进一步表明,Mg-Al系合金中相结构稳定性提高的主要原因在于:SbBi合金化后,体系费米能级以下低能级区成键电子数的增多,其来源主要是Mg(s)Mg(p)Al(p)Bi(d)Sb(d)的价电子。

 

关键字: Mg17Al12相;结构稳定性;热力学性能

Mechanism of Sb, Bi alloying on improving heat resistance properties of Mg-Al alloy
ZHOU Dian-Wu1, LIU Jin-shui2, LU Yuan-zhi1, ZHANG Chu-hui1

(1. State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, Hunan University,Changsha 410082, China;2. School of Materials Science and Engineering, Hunan University, Changsha 410082, China)

Abstract:By using Dmol 4.1 program based on the density functional theory, heat of formation, cohesive energy, thermodynamic properties and density of states (DOS) of the alloying system were investigated to explain the mechanism of the influence of Sb, Bi alloying on improving heat resistance properties of Mg-Al alloy. The results show that the structure of these phases can exist and be stable when the Mg atoms at the positions Ⅰ, Ⅱ of the Mg17Al12 phase are substituted with Sb, the Mg atoms at the positions Ⅰ are substituted with Bi, which shows that Sb and Bi are little soluted in Mg17Al12 phase. By comparing the stable Mg17Al12 phase with Sb or Bi addition, it is found that Mg17Al12 phase stability is improved, and Mg17Al12 solid solutions substituting Mg atoms at positions Ⅱ with Sb has the highest structural stability, next substituting Mg atoms at positions Ⅰ with Sb, finally substituting Mg atoms at positions Ⅰ with Bi, whereas the structures of Mg3Sb2 and Mg3Bi2 are more stable than that of Mg17Al12 solid solutions with Sb, Biadditions. By calculating the thermodynamic properties of Mg-Al alloy, it is found that the improved heat resistance properties of the alloying system are caused by forming the Mg17Al12 phase and intermetallic Mg3Sb2 and Mg3Bi2 with higher structural stability, which is not changed with the elevated temperature. Compared with the density of states (DOS) of the alloying system, the increase of the structural stability of Mg-Al alloy with Sb or Bi additions attributes to an increase in the bonding electron numbers at lower energy level below Fermi level, which mainly originates from the contribution of the valence electron numbers of Mg(s), Mg(p), Al(p), Bi(d) and Sb(d) orbits.

 

Key words: Mg17Al12 phases; structural stability; thermodynamic properties

ISSN 1004-0609
CN 43-1238/TG
CODEN: ZYJXFK

ISSN 1003-6326
CN 43-1239/TG
CODEN: TNMCEW

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