First-principles Calculation Of The Effect Of Doping On The Passivation Behavior Of Aluminum In Atmospheric Environment

Aluminum alloy materials are widely used in engineering practice due to their excellent properties.However,in corrosive environments,pitting corrosion is easily formed on the surface of the material due to the interaction between environmental media and material elements,which affects the strength and service life of the structure.The passivation film on the surface of aluminum alloy can protect the inner aluminum alloy matrix,and the pitting corrosion on the surface of aluminum alloy usually occurs in the environmental medium that makes it passivated.When the aggressive active ions are adsorbed to the surface of the passivation film,complex chemical reactions will occur,causing the passivation film to break,changing the protection performance of the passivation film,and causing pitting initiation.The thickness and structure of the passive film are usually related to the material composition and environmental factors.Therefore,studying the passivation behavior of aluminum alloy will have important theoretical significance for further improving the anti-corrosion design of the material.In order to further improve the performance of aluminum and its alloy materials,doping process measures are usually used in engineering.However,due to the sensitivity of doping elements to the environment,the structure,composition and corresponding protection ability of the passivation film on the surface of aluminum alloy will be affected.The passivation behavior of aluminum alloy surface is very different from the volume of the alloy itself,and the reaction time is very short.It is still difficult to study the process by experimental means.Based on the first-principles method,the chemical reaction between the surface of aluminum matrix or passivation film and gas molecules and ions in the environment can be described from the interaction between atoms,and the effect of doping on the passivation behavior of aluminum in the atmospheric environment can be revealed.In this paper,the influence mechanism of Mn,Ni and Si elements in aluminum alloy on the passivation process of aluminum in atmospheric environment was studied by first-principles calculation.Firstly,through the establishment of the model and the setting of the parameters,the effects of the type and amount of doping elements on the adsorption behavior of different numbers of oxygen molecules on the surface of pure aluminum were calculated.The results show that the electronic properties of the system determine the adsorption properties.The outermost electron orbit is the main factor that determines the influence of different doping elements on the formation of passivation film in the atmospheric environment.The influence of doping type and amount on the adsorption of oxygen molecules on the surface of pure aluminum is related to the number of oxygen molecules adsorbed on the surface.When the number of adsorbed oxygen molecules is less than or equal to 2,Mn,Ni and Si doping inhibits the adsorption of oxygen molecules,and as the number of surface doping elements increases.This inhibition will not change.When the number of adsorbed oxygen molecules is greater than two,Ni and Si doping promotes the adsorption of oxygen molecules.At this time,as the number of doped atoms increases,the effect of promoting oxygen molecule adsorption is better.When the doping amount of Mn atoms gradually increases,the adsorption of oxygen molecules will be inhibited.Among them,the increase of Ni doping element promotes the adsorption of oxygen molecules,mainly through the migration of oxygen atoms to the surface to thicken the oxide film,while Mn and Si atoms mainly increase the density of the oxide film by increasing the density of surface atoms,thereby increasing the corrosion resistance of the oxide film.Secondly,the effect of doping on the adsorption of water molecules by pre-oxidized Al(111)was studied by adding water molecules in the above model.Finally,it was found that the doping of Si and Mn atoms always inhibited the adsorption of water molecules,regardless of the number of pre-adsorbed oxygen atoms on the surface,and the doping of Ni atoms always promoted the adsorption of water molecules.However,only when the number of pre-adsorbed oxygen molecules is 2,the water molecules will dissociate,so that the original passivation film is hydroxylated and the composition changes.