Mg-Al-Ca合金中第二相价电子结构计算与强化机制分析

Calculation of Valence Electron Structures and Analysis on Strengthening Mechanism of the Second Phase in Mg-Al-Ca Alloy

摘要:

基于EET理论及其与程氏改进的TFD理论的结合，计算并分析了Al2Ca、Mg2Ca价电子结构及Al2Ca(111)//α-Mg(1121)(11)、Mg2Ca(001)//α-Mg(0001)界面电子结构。Al2Ca最强键(nA=0.397 06)与Mg2Ca最强键(nA=0.302 45)的键合强度均远大于基体α-Mg(nA=0.111 99)的键合强度，极大地阻碍了位错运动和晶界滑移，提高了合金的强度；第二相Al2Ca和Mg2Ca的单位体积成键能力FV值分别为99.25和47.66，与γ-Mg17Al12(Fγ-Mg17Al12V＝44.22)相比较，Al2Ca的自身的稳定性更好，促进了合金高温性能的提高，Mg2Ca自身的稳定性较差，对合金高温性能的提高作用不大；第二相与基体形成的界面的电子密度差大于Mg17Al12与基体形成的界面γ-Mg17Al12(110)//α-Mg(0001)电子密度差，界面强化效果更好，能有效地提高合金的工作温度；第二相与基体界面电子密度差较大，阻碍晶粒长大的效果较好，从而使基体的组织得以细化，并增加了γ-Mg17Al12的析出形核率，提高了合金的力学性能。

Abstract:

The valence electron structures of Al2Ca and Mg2Ca, and the interface electron structures of Al2Ca(111)//α-Mg(), Mg2Ca(001)//α-Mg(0001) are calculated and analyzed based on the empirical electron theory of solids and molecules and an improved Thomas-Fermi-Dirac(TFD) theory. The strongest bond (nA=0.397 06) of Al2Ca and the secondary strong bond (nA=0.302 45) of Mg2Ca greatly hinder the dislocation movement and grain-boundary sliding, so that the alloy’s intensity is enhanced. Compared the FV value of γ-Mg17Al12 (＝44.22), the total bond-forming ability in unit volumevalue of Al2Ca and Mg2Ca is 99.25 and 47.66, respectively. It shows that the high temperature stability of Al2Ca is better and its existence is advantageous to improve the high temperature performance of Mg-Al alloy. The interface electronic density difference of the second phase in crystal boundary and the substrate is greater than that of the γ-Mg17Al12(110)//α-Mg(0001), the γ-Mg17Al12 and the substrate, with a better interface strengthening effect effectively to increase the operation temperature of Mg-Al alloy. The bigger difference of the interface electron densities would prevent grain growth and a finer microstructure can be obtained during solidification, as a result, the nucleation rate of γ-Mg17Al12 is increased and the mechanics properties of Mg-Al alloy are enhanced.