The Study Of Corrosion Behavior Of Pure Aluminum And Its Alloys In Different Environment Applied By Wire Beam Electrode

Nowadays,aluminum and its alloys,which are used for most corrosion resistance materials,have played vital roles in the marine field,and their corrosion resistance ability directly determines the service life of metallic materials.In the paper,a method of Wire Beam Electrode(WBE)is used to study the corrosion behaviors of aluminum and aluminum alloys under different environments,aiming to explore the passivation film corrosion and formation laws of aluminum and aluminum alloys in a simulated marine environment,to analyze their corrosion characteristics and varied laws under different temperatures,and to investigate their corrosion characteristics and laws in a crevice structure.Also,a method of cemented carbide composite coating on aluminum alloy surface was proposed,which provides a reference for postponing the corrosion of materials in the marine environment.The conclusions of this work are as follows:(1)This work selected pure aluminum(1050)and three kinds of aluminum alloys(5052,6061,7075)as the working parts of each wire beam electrode.The above four kinds of WBE were prepared to carry out the electrochemical corrosion experiments of the passivation films on their surfaces in ocean environment.The results show that the quality and rate of passivation film are related to the corrosion potential.The more positive the corrosion potential is,the faster passivation film formed is.The corrosion degree of alloy passivation film is related to the corrosion current.When the corrosion current is greater,the corrosion damage degree of passivation film is much serious;at the same time,in the case of mechanical damage,the obvious local corrosion occurred in the scratch area at the early stage of immersion.With the increase of test time,the passivation film repairing rate of pure aluminum and its alloys followed the law:1050>5052>6061>7075.The passivation film on the surface of pure aluminum was repaired quickly in a short time after being damaged,while the corrosion tendency of scratch area of 7075 aluminum alloy was serious,and the passivation film in the scratch area was not repaired until the end of the test.(2)The electrochemical corrosion tests of four materials above-mentioned in3.5wt.% Na Cl solution under 5,20,35 and 55 ℃ were carried out based on WBE of aluminum and its alloys with composition gradient distribution.The results showed that: the temperature had a direct effect on the forming rate and quality of passivation film of the metal surfaces.By comparing the conditions at three different temperatures(5,20,35 ℃),the potential of electrode surface became more and more positive with the increase of temperature,indicating that the formation rate of passivation film was fast as the temperature increased from 5 ℃ to 35 ℃.However,when the temperature reached 55 ℃,aluminum alloy did not show a trend of more damaged corrosion.The high temperature promoted the formation and self-repairing rate of passivation film,which resulted in the reduction in the localized current.Meanwhile,it shows that the passivation film on aluminum alloy surface grew and developed in a dynamic cycle of film formation-destruction-self-repairing-destruction in the 3.5wt.% Na Cl solution.(3)The electrochemical corrosion tests of aluminum and its alloys were carried out based on WBE method under different crevice spacing.Results showed that the corrosion behavior was obvious when the spacing was 206 μm.Then the corrosion behaviors of aluminum and its alloys in 3.5 wt.% Na Cl solution under crevice spacing of d=206 μm were studied by the WBE,together with dynamic potential polarization and electrochemical impedance spectroscopy.The results also showed that the crevice corrosion of 6061 aluminum alloy was most sensitive,while the crevice corrosion at the beginning of the test was not obvious,and the average potential in the flat area was lower than that in the crack area;while at 10 h,the crevice corrosion began to appear,and the average potential of the two areas showed a trend of reversal.Then the average current reversal phenomenon also occurred in the crevice area.The corrosion occurred in the area after a long time of anode current.In addition,a Ti Al N coating was deposited on the surface of aluminum alloy wire electrode by an arc ion plating device.The electrode coating prepared at 380 ℃ was compact,complete and showed excellent corrosion resistance,which provided a reference scheme for solving various corrosion problems of aluminum alloys.