Al-Zn-Mg-Cu系铝合金中不同区域电子结构及应力腐蚀机理分析

利用计算机编程建立了Al--Zn--Mg--Cu合金 (7175铝合金) 中α--Al, η相及α--Al大角度晶界原子集团模型, 采用递归法计算 合金中Zn, Mg, Cu和H的环境敏感镶嵌能、原子间相互作用能、Fermi能级和态密度等电子结构参数, 分析了合金的应力腐蚀机理. 计算 结果表明: Mg, Cu和H容易在晶界偏析. Mg对H具有吸引作用, 促进H在晶界偏析, 引起晶界氢脆; Zn增大晶界与晶内的电位差, 降低合 金抗腐蚀性; Cu能减小晶界与晶内Fermi能级差, 降低晶界与晶内的电位差, 具有减缓合金腐蚀的作用. 计算结果还表明: η相的Fermi能 级最高, 腐蚀过程中作为阳极优先溶解. 由于η相俘获H, 当晶界析出断续η相时可减弱晶界H的偏析, 提高抗腐蚀性; 但晶界连续分布η相则形成腐蚀通道, 加速腐蚀进程.

ELECTRONIC STRUCTURE OF DIFFERENT REGIONS AND ANALYSIS OF STRESS CORROSION MECHANISM OF Al-Zn-Mg-Cu ALLOYS

The atomic cluster models of α--Al, η--phase and large angle grain boundary of α--Al in Al--Zn--Mg--Cu alloys have been constructed by computer program. The environment--sensitive embedding energies of Zn, Mg, Cu and H atoms, interaction energies, Fermi energies and densities of state have been calculated by recursion method. The stress corrosion cracking behavior of Al--Zn--Mg--Cu alloys has been analyzed according to the calculated electronic parameters. The results show that Mg, Zn and H atoms are easy to segregate on grain boundaries. Mg promotes the segregation of H on grain boundary, which leads to the embrittlement of grain boundary because of the attraction of Mg to H. Zn increases the difference of electrode potential between boundary and grain, which deteriorates the stress corrosion resistance of Al--Zn--Mg--Cu alloys. Cu reduces the difference of Fermi energies between grain and grain boundary, and lowers the electrode potential difference between grain and grain boundary, which helps to slow up the corrosion process. The calculated results also indicate that the Fermi energy of η--phase is the highest, so η--phase will decompose firstly in the corrosion process as anode. Discontinuous distribution of η--phase along grain boundary can weaken the segregation of H on the grain boundary because of the capture of η--phase to H, and improve the stress corrosion resistance of Al--Zn--Mg--Cu alloys, while the corrosion channel can form and speed up the corrosion process when η--phase distributes continuously on the grain boundary.