結(jié)構(gòu)穩(wěn)定性的第一原理研究
(1. 湖南大學(xué) 汽車車身先進設(shè)計制造國家重點實驗室，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CASTEP和DMol程序軟件包，從合金形成熱、結(jié)合能、熱力學(xué)性能和電子結(jié)構(gòu)等方面，研究Sn合金化MgZn2相及Mg2Sn相的結(jié)構(gòu)穩(wěn)定性，探討Sn合金化改善ZA62鎂合金抗蠕變性能的機理。結(jié)果表明：當(dāng)Sn和Al分別置換ZA62鎂合金中MgZn2相的Zn(Ⅰ)和Zn(II)原子時，僅Sn與Al置換的MgZn2相中Zn(Ⅰ)原子能形成穩(wěn)定的MgZn2固溶體結(jié)構(gòu)，而Sn在MgZn2相中的固溶量有限；與合金化形成的固溶體結(jié)構(gòu)相比，其穩(wěn)定性比未合金化時的弱，而析出的第二相金屬間化合物Mg2Sn的結(jié)構(gòu)比MgZn2的更穩(wěn)定。而不同溫度下熱力學(xué)性能的計算結(jié)果表明：合金體系中形成了結(jié)構(gòu)穩(wěn)定性強的Mg2Sn，其結(jié)構(gòu)穩(wěn)定性在溫度373～473 K的范圍內(nèi)并不因溫度的升高而消失，仍比MgZn2的高；由于ZA62鎂合金體系中形成了高熱穩(wěn)定性的Mg2Sn相，Sn合金化有利于ZA62鎂合金抗蠕變性能的提高。電子態(tài)密度和Mulliken電子占據(jù)數(shù)的分析結(jié)果表明：與MgZn2、Mg2AlZn3及Mg2SnZn3固溶體相比，熱穩(wěn)定性強的Mg2Sn相形成的主要原因在于Mg2Sn 體系中存在強烈的離子鍵與共價鍵的共同作用。
關(guān)鍵字: ZA62合金；MgZn2相；Mg2Sn相；結(jié)構(gòu)穩(wěn)定性；熱力學(xué)性能；第一性原理；Sn合金化
Sn alloying MgZn2 phase and Mg2Sn phase
（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 CASTEP and DMol program based on the density functional theory, the heat of formation, the cohesive energy, the thermodynamic properties and the electronic structure of the alloying system were investigated to study the structural stability of Sn alloying MgZn2 phase and Mg2Sn phase and explain the mechanism of the influence of Sn alloying on improving the creep resistance properties of ZA62 magnesium alloy. The results show that the structure of these phases can exist and be stable when the Zn atoms at the I positions of the MgZn2 phase are substituted with Sn and Al, whereas, it is also found that Sn is little solved in MgZn2 phase. By comparing with the stable MgZn2 phase, it is found that the stability of MgZn2 phase is reduced with Sn addition, and the structure of intermetallic compound Mg2Sn is more stable than that of MgZn2 phase. By calculating the thermodynamic properties of different phases, it is found that the improved creep resistance properties of ZA62 magnesium alloy are caused by forming intermetallic compound Mg2Sn with higher structural stability which is not changed with the elevated temperature in the range of 373−473 K. The
calculations of the density of states (DOS) and Mulliken electronic populations of the alloying system show that the form of Mg2Sn with the highest structural stability in ZA62 magnesium alloy with Sn addition attributes to the ionic bond and covalent bond in the bonding electron numbers compared with those of MgZn2 phase, Mg2AlZn3 and Mg2SnZn3 solid solutions.
Key words: ZA62 alloy; MgZn2 phase; Mg2Sn phase; structural stability; thermodynamic property; first-principle; Sn alloying
