The Influence Of Strain And Adsorbate On Typical Surface/Interface Properties Of Aluminum Alloy Based On Density Functional Calculation

Aluminum(Al)alloy has many advantages such as low density,high strength,good corrosion resistance,and easy processing and forming.Therefore,it is widely used in aviation,marine,petroleum and chemical industries and other national economic fields.Al alloys will undergo pitting corrosion or stress corrosion during service,which will further lead to the failure of the alloy structure and function,especially the stress corrosion,which is often a serious obstacle to the further development of high-strength Al alloys.The current research generally believes that the migration and accumulation of hydrogen and the unevenness of the internal and external stress of the material have an important impact on the stress corrosion cracking of high-strength Al alloys.In this paper,the first-principles calculation method is used to simulate and study the interaction process between various adsorbents and the metal surface.The influence of hydrogen atoms on the initiation of phase interface cracks is analyzed,and the relationship between the strength of the alloy precipitated phase/matrix interface and the the micro-mechanism of fracture resistance.First,the co-adsorption behavior of Cl-,H2O and OH-on the Al surface was studied,the microscopic conditions of the dissociation of H2O molecules were analyzed,and the effects of strain and Cl-on the dissociation reaction and corrosion of the metal surface were explored.By analyzing the stable configuration of the Al surface under strain conditions,it is found that large strains are not suitable for describing the surface energy and vacancy formation energy of the model.Strain and Cl-damage the surface due to the interaction between vacancies and Al atoms and O-Al.For different H2O/OH-ratios,the dissociation of H2O molecules on the Al surface needs to meet three sufficient conditions,1)H2O and OH-must be adjacent;2)H in H2O must point to the O atom in OH-;3)Two H in H2O cannot point to two adjacent O atoms at the same time.Cl-and OH-play different roles in the dissociation of H2O molecules,because Cl-does not directly participate in the dissociation reaction of H2O,but plays a catalytic role.Strain will lower the transition state energy barrier of the H2O dissociation reaction and promote the destruction of the Al surface by H2O molecules.Secondly,the effects of strain on the fracture process of the combined body model(C-body model)and combined surface model(C-surface)composed of?'(Mg2Zn3Al4)and Al matrix in the Al-Cu-Mg-Zn alloy,and H The influence of the adsorption and infiltration of atoms on the surface,the microscopic mechanism of hydrogen-induced crack initiation was explored.It was found that for the C-body model,the fracture mode was brittle fracture,and the atoms in the Al phase near the phase boundary showed obvious relaxation and reconstruction.For the C-surface model,the fracture mode is ductile fracture,and the atoms at the interface become disordered under tensile strain.By designing the three stages of hydrogen-induced crack initiation,the influence of the coupling effect of hydrogen atoms and strain on C-surface fracture was studied.Due to the difference in hydrogen atom adsorption sites and embedded positions,the fracture forms of the C-surface model in the three stages are different,and the repulsion between hydrogen atoms is the root cause of cracks at the phase boundary.The hydrogen-induced cracking at the phase boundary is mainly affected by the interaction between Mg-H and the properties of the ?'phase.The fracture at the ?'/Al phase interface plays a key role in the failure of the Al-Cu-Mg-Zn alloy.Finally,the relationship between the bond strength and fracture resistance of the ?'/Al interface in the Al-Mg-Si alloy was studied.The results show that the theoretically designed interface models(LS3T4 and LS4T4)have higher thermodynamic stability under the conditions of Si enrichment than the experimentally observed models.The calculation results of the adhesion work of the interface model show that the LS1T2 and LS2T2 models have strong interface bonding strength,and the size of the adhesion work is mainly affected by the(?'terminal.According to Griffith fracture theory,the fracture between ?'/Al phase in Al-Mg-Si alloy depends on the Si/Mg content ratio at the interface.The bonding strength of the interface structure is related to the bond charge of the Mg-Al and SiAl bonds at the interface.The analysis of the electronic structure shows that compared with the Mg-Al bond,the bonding force of the Si-Al bond is stronger,and the angle between Si-Al and the interface(?Si-Al)also has a great influence on the bonding strength of the interface.The angle with the interface(?Mg-Al)affects the fracture resistance of the ?'/Al interface.The interface strength and fracture resistance are also related to the hybridization of high-level electron orbitals.Therefore,controlling the types and angles of atomic bonds at the interface is one of the methods to affect the strength and fracture resistance of the alloy interface.Through the above research,the microscopic process of the interaction between the Al surface of the vacancy defect and various adsorbents under the action of strain is obtained,and the microscopic mechanism of strain affecting the dissociation of H2O molecules is refined.The conditions of strain-induced composite surface fracture were obtained,and the mechanism of hydrogen atoms in the process of strain-induced fracture of composite surfaces was explained.The the relationship between interface bonding performance and the mechanical properties of precipitates,and the relationship between interface bonding strength and interface fracture resistance were established.