稀土对镁合金应力腐蚀影响电子理论研究

建立了镁合金纯净晶界及其析出Mg₁₇Al₁₂相的晶界原子集团，应用实空间的递归方法计算了铝、稀土元素在晶界的偏聚能，晶界处铝、稀土原子间相互作用能和不同体系的费米能级.讨论了铝、稀土在晶界的偏聚行为，铝、稀土原子间的相互作用与有序化的关系及稀土对镁合金晶间应力腐蚀影响的物理本质.研究发现：铝、稀土原子偏聚于晶界；铝原子间相互排斥，在晶界区形成有序相Mg₁₇Al₁₂，稀土原子间互相吸引，形成原子团簇；稀土原子团吸引铝原子，使铝原子渗入稀土团簇中，形成稀土化合物.因此，稀土具有抑制铝在晶界形成导致应力腐蚀的阴极相Mg₁₇Al₁₂的作用，提高镁合金的晶间应力腐蚀抗力. 关键词： 电子理论 镁合金 应力腐蚀 稀土

Electronic theoretical study on the influence of rare earth on the stress corrosion in magnesium alloy

The atomic models of pure boundary and that with Mg₁₇Al₁₂ of α phase in magnesium alloy were set up. The segregation energies of Al and rare earth atoms, the interaction energies between Al and/or rare earth atoms, and the Fermi energy levels of different systems were calculated by using recursion method. The Al and rare earth segregation at the grain boundaries, the relationship between the interaction of Al or rare earth atoms and the ordering tendency, as well as the physical nature of the influence of rare earth on the stress corrosion of magnesium alloy were discussed. Calculation results show that: Al and rare earth atoms segregate at grain boundaries, and Al atoms repel each other, leading to the formation of the ordered Mg₁₇Al₁₂ phases in the grain boundaries. But rare earth atoms attract each other, so atom clusters are formed in the grain boundaries. The rare earth atom cluster can attract Al atoms, make the Al atoms to infiltrate into the rare earth atom cluster, forming rare earth compound. Therefore, rare earth have the effect of restraining the forming of Mg₁₇Al₁₂ along grain boundaries which functions as the cathode of magnesium alloy that leads to corrosion, this reducing the sensibility of stress corrosion.