A Cross-scale Calculation Of Passivity And Intergranular Cracking In Aluminium

A cross-scale calculation combined with first-principles and cohesive finite element method is performed to examine the passivity and hydrogen induced intergranular cracking in Aluminum.The adsorption of H2O and O2 was investigated to study the formation mechanism of passive film.The results revealed that the passive film was formed by the co-adsorption of H2O and O2 and thickened by the O atoms migration from surface to inner structure.The pitting initiation was studied by the interaction between Cl-and passive film using first-principles calculations,which was proved that the pitting initiation tended to Cl-adsorption induced oxide thinning instead of permeation mechanism.The adsorption,solution and diffusion of H atom was performed along Al(111)surface to obtain the most stable adsorption and solution site and the diffusion energy barrier.A 120-atom grain boundary(GB)and grain models were constructed to characterize the solution and duffusion H atom.H atom is energetic favourable to dissolve in sites of GB and the ability of H diffusion in GB is stronger than that in grain inner.H atom in interstitial site of grain will be easy to migrate into GB by addition of Al atom vacancy.Besides,the introduction Al atom vacancy can decrese the energy barrier of H diffusion in grain inner,while the promotion of Al atom vacancy on the H diffusion in GB is related to its migratied direction.The strength of GB characterized by its covehesive energy was calculated by first-principles method,which decreased with the increasing H concentration segregated in GB.The cohesive energies were input into cohesive finite element calcultaions as the fracture energies to simulate the intergranular cracking,which was a cross-scale study.The application of the cross-scale approach is very efficient for investigating the evolution of hydrogen induced intergranular cracking.The work of this study provided a scheme using a cross-scale calculation from atomic scale to macro-scale to study the behavior and mechanism of passivity and hydrogen induced intergranular cracking in metals.