Preparation And Corrosion Resistance Of Al Based Amorphous/nanocrystalline Coating By Arc Spraying

Al-based amorphous alloys have attracted much attention due to their high specific strength and good corrosion resistance.And they are potential light-weight structures and corrosion-resistant materials in aerospace,marine and other fields.However,due to the characteristics of the low Glass Forming Ability of Al-based alloy,it is very difficult to prepare the bulk amorphous,which limits the large-scale application.The preparation of Al-based amorphous anti-corrosion coating by thermal spraying technology has a strong practical value in engineering.In this paper,the single roller rapid quenching technique is used to prepare ribbons,and the glass forming ability and corrosion resistance potential of various Al-based ribbons are studied.According to the results of the rapid solidification research,the two component systems of AlFeNbNi and AlFeNbSi were selected,and the amorphous coating with excellent corrosion resistance was prepared by arc spraying technology,and the corrosion resistance of the coating in the marine environment was evaluated.Finally,the effects of laser remelting on the microstructure,hardness and corrosion resistance of two amorphous coatings were studied.The results show that AlFeNbNi and AlFeNbSi ribbons with amorphous structure have been prepared by the single roller rapid quenching technique.The ribbons of both components show significant passivation characteristics on Tafel curve,and the self-corrosion current density is very low,which shows good corrosion resistance potential.The results of Mott-Schottky curves further show that the passive films formed by the two kinds of ribbons are p-n bipolar semiconductors.The carrier density of AlFeNbSi ribbon is one order of magnitude lower than that of AlFeNbNi ribbon,and the flat potential of AlFeNbSi ribbon is more negative,which means better corrosion resistance.Both AlFeNbNi and AlFeNbSi coatings prepared by arc spraying contain about 30%amorphous structure.The EDS results of the coating cross section show that the alloy elements such as Nb and Ni are segregated and oxidized to some extent.There are a few defects such as pores and cracks in the coating,among which there are more micro defects in AlFeNbSi coating.The hardness test results show that the average hardness of AlFeNbNi coating is HV0.2268.4,and the average hardness of AlFeNbSi coating is HV0.2341.4.The results of Tafel test show that there are no passivation in the two coatings.However,the self-corrosion current densities of AlFeNbNi and AlFeNbSi coatings are only 5.2 ?A·cm-2 and 6.9 ?A·cm-2,respectively,which are significantly lower than those of Q345 matrix,indicating that the coatings of both components have good anti-corrosion effect.During the seawater immerse corrosion,the macromorphology of the test plate after 14 weeks' immersion shows that there is no obvious corrosion phenomenon of AlFeNbNi and AlFeNbSi coatings,while the Q345 substrate soaked at the same time has entered the comprehensive corrosion stage.The evolution of the micro morphology of the coating surface shows that the corrosion process of AlFeNbNi coating is as follows:the surface oxide film is damaged by pitting corrosion,and maintains the micro layered corrosion characteristics,accompanied by slight pitting corrosion;the corrosion process of AlFeNbSi coating is as follows:after the oxide film is eroded,there are pores and cracks,and the coating continues to have pore corrosion,showing the characteristics of loose porosity.The electrochemical test on the surface of the coating after seawater immerse corrosion showed that the passivation of AlFeNbNi coating occurred.The self-corrosion potential gradually stabilized at-0.75VSCE with the immersion time extended,and the self-corrosion current density gradually decreased to 1.77 ?A·cm-1.There was no passivation in AlFeNbSi coating,and the self-corrosion potential decreased to-0.73 VSCE and the self-corrosion current density decreased to 0.48 ?A·cm-2 with the increase of immersion time.The passivation film of AlFeNbNi coating formed after immersion for a long time is attributed to the effect of Ni element in the coating,which shows good corrosion resistance.The passivation of AlFeNbSi coating was not observed after immersion for a long time.Laser remelting of as-sprayed AlFeNbNi and AlFeNbSi coatings resulted in the disappearance of defects such as pores in the coating and the improvement of the structure of the coating.The amorphous content of the coating decreased from 30%to 0%.A good metallurgical bond was formed between the coating and the substrate.After remelting,the highest hardness of AlFeNbNi and AlFeNbSi coatings is close to HV0.2600,and the lowest hardness is about HV0.2450.The hardness increases along the surface.The electrochemical test results showed that the self-corrosion potential of AlFeNbNi remelting layer is increased from-0.646 VSCE to-0.472 VSCE,and the corrosion current density is reduced to about 1/3 of the arc-spraying coating,and the passivation phenomenon is obvious due to the redistribution of alloy elements.The corrosion resistance of AlFeNbSi coating is also improved,but there is no passivation phenomenon,and it is easy to be damaged by Cl-.