Pb-Mg-Al合金腐蚀机理的电子理论研究

为了了解Pb-Mg-Al合金腐蚀的物理本质, 本文采用基于第一性原理的赝势平面波方法系统地计算了Pb-Mg-Al合金中各物相的结合能、费米能级和局域态密度等电子结构参数, 分析了合金的电化学腐蚀机理. 计算结果表明：Pb-Mg-Al合金中各主要组成物相稳定性大小关系为 Mg₁₇Al₁₂>Mg₂Pb>Mg；Mg,Mg₂Pb和Mg₁₇Al₁₂的费米能级存在E_f(Mg)>E_f(Mg₂Pb)>E_f(Mg₁₇Al₁₂)的关系, 说明Mg最容易失去电子, Mg₂Pb次之, Mg₁₇Al₁₂最难；局域态密度表明, 在同样的外界条件下, 体系中Mg相和Mg₂Pb相对于Mg₁₇Al₁₂均处于不稳定的状态, 容易失去电子, 即容易发生腐蚀. Pb-Mg-Al合金体系中不同物相的费米能级差构成了电化学腐蚀的电动势, 导致电子从费米能级高的Mg相和Mg₂Pb相流向费米能级低的Mg₁₇Al₁₂相, 使Pb-Mg-Al合金发生腐蚀.

Electronic theory of the mechanism of corrosion of Pb-Mg-Al alloy

The cohesive energies, Fermi energies and local density of states (LDOS) are calculated by the first-principles based on pseudopotential plane wave method in this paper to investigate the physical nature of corrosion of Pb-Mg-Al alloy. The mechanism of electrochemical corrosion is analyzed according to the calculated electronic structure parameters. The results show that the stable phase in Pb-Mg-Al alloy is Mg₁₇Al₁₂>Mg₂Pb>Mg. The Fermi energy (E_f) values of these phases with E_f(Mg)>E_f(Mg₂Pb)>E_f (Mg₁₇Al₁₂) indicate that Mg is most likely to lose electrons while Mg₁₇Al₁₂ is difficult. LDOS result reveals that Mg and Mg₂Pb phases are unstable compared with Mg₁₇Al₁₂ in the same external conditions, they are more likely to lose electrons and easier to corrod. The difference in Fermi energy between different phases in Pb-Mg-Al alloy forms the electrodynamic force of the electrochemical corrosion, which leads electrons to flow from the Mg and Mg₂Pb phases with higher Fermi energy to Mg₁₇Al₁₂ phase with lower Fermi energy, further to corrode in Pb-Mg-Al alloy.