((1. 湖南大學(xué) 汽車車身先進(jìn)設(shè)計制造國家重點(diǎn)實(shí)驗(yàn)室，長沙 410082；2. 湖南大學(xué) 材料科學(xué)與工程學(xué)院，長沙 410082))
摘 要: 采用基于密度泛函理論的Dmol 4.1程序，從合金形成熱、結(jié)合能、熱力學(xué)性能和態(tài)密度等方面，研究Sb、Bi合金化提高Mg-Al系合金抗蠕變性能的影響機(jī)理。結(jié)果表明：Sb、Bi分別置換Mg-Al系合金Mg17Al12相中Mg(Ⅰ)，Mg(Ⅱ)，Mg(Ⅲ)和Al原子時，僅Sb置換Mg17Al12相中Mg(Ⅰ)，Mg(Ⅱ) 原子，Bi置換Mg17Al12相中Mg(Ⅰ)原子能形成穩(wěn)定的Mg17Al12固溶體結(jié)構(gòu)，這表明Sb、Bi在Mg17Al12中固溶量有限。進(jìn)一步比較合金化形成穩(wěn)定的固溶體結(jié)構(gòu)，發(fā)現(xiàn)Sb、Bi合金化后，固溶體結(jié)構(gòu)的穩(wěn)定性比未合金化時增強(qiáng)，其中，Sb置換Mg17Al12相中Mg(Ⅱ)原子時，其結(jié)構(gòu)穩(wěn)定性最高，其次Sb置換Mg17Al12相中Mg(Ⅰ)原子，再次Bi置換Mg17Al12相中Mg(Ⅰ)原子；而析出金屬間化合物Mg3Bi2和Mg3Sb2，比相應(yīng)合金化Mg17Al12固溶體的結(jié)構(gòu)更穩(wěn)定。不同溫度下熱力學(xué)性能的計算發(fā)現(xiàn)，合金體系中形成了結(jié)構(gòu)穩(wěn)定性高的Sb、Bi合金化Mg17Al12固溶體以及金屬間化合物Mg3Sb2和Mg3Bi2，這些相高的結(jié)構(gòu)穩(wěn)定性并不因溫度的升高而消失，其結(jié)構(gòu)穩(wěn)定性仍比Mg17Al12相高，因此Sb、Bi合金化提高了Mg-Al系合金的抗蠕變性能。電子態(tài)密度的分析結(jié)果進(jìn)一步表明，Mg-Al系合金中相結(jié)構(gòu)穩(wěn)定性提高的主要原因在于：Sb、Bi合金化后，體系費(fèi)米能級以下低能級區(qū)成鍵電子數(shù)的增多，其來源主要是Mg(s)、Mg(p)、Al(p)、Bi(d)和Sb(d)的價電子。
關(guān)鍵字: Mg17Al12相；結(jié)構(gòu)穩(wěn)定性；熱力學(xué)性能
（(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
