杂质对镁合金耐蚀性影响的电子理论研究

利用大角重位点阵模型建立了Mg合金［0001］对称倾斜晶界模型，应用实空间的连分数方法计算了杂质在晶界的偏聚能，杂质原子间相互作用能和不同体系的费米能级，讨论了杂质在晶界的偏聚行为，杂质间的相互作用与有序化的关系及杂质对镁合金腐蚀性能影响的物理本质. 计算结果表明，杂质原子偏聚于晶界，且主要偏聚于晶界的压缩区；杂质原子间相互排斥，因此在晶界区形成有序相；费米能级与材料的腐蚀电位存在这样的关系：材料的费米能级越高，其腐蚀电位就越低，容易被腐蚀，相反费米能级低，其腐蚀电位就高，不容易腐蚀. 体系中成分不同区域的费米能级差导致电子从费米能级高的区域流向费米能级低的区域，正是费米能级差构成了镁合金电化学腐蚀的电动势. 关键词： 电子理论 晶界偏聚 镁合金 腐蚀机理

Electronic theoretical study of the influence of impurities on corrosion resistance of magnesium alloy

The atomic structure model of symmetric ［0001］ tilt boundary of α phase in magnesium alloy was set up by using the concept of coincidence-site lattice (CSL). The segregation energies of impurities, the interaction energies between impurities and fermi levels of different systems at grain boundary (GB) were calculated by using recursion method. The segregation behaviour of impurities, the relationship between the interaction between impurities and the ordering tendency, as well as the physical nature of the influence of impurities on corrosion resistance of magnesium alloy were discussed. Calculation results show that impurity atoms segregate to GB, and are apt to occupy the sites in the compressed region of GB. Impurity atoms repel each other, therefore form ordered phases in the region of GB. The relationship between the fermi level of a kind of material and its equilibrium potential is: the higher the fermi level is, the lower the equilibrium potential is; and vice versa. The difference of fermi level of regions with different composition in a system leads to the flow of electrons from the region with high fermi level to the region with low fermi level. It is just the difference of fermi levels that forms the electrodynamic force of the electrochemical corrosion in magnesium alloys.