摘要
Abstract
To clarify the influence mechanism of process transfer time,i.e.,natural oxidation time after pretreatment,on the formation behavior and properties of the sol-gel film on the surface of titanium alloy,the Ti-6Al-4V(TC4)alloy surface was naturally oxidized for different times from 0 to 36 h after activation pretreatment to simulate the transfer time before the painting process after the pretreatment.The effect of natural oxidation time on the surface electrochemical properties of TC4 alloy was investigated by open circuit potential(OCP)detection and electrochemical impedance spectroscopy(EIS).A mixed sol-gel of silica sol and zirconium sol was prepared,and the wettability of sol-gel and TC4 samples with different natural oxidation times was measured by optical contact angle measuring instrument.And a sol-gel conversion film was prepared by dip-coating method,and the effect of natural oxidation time on the interface morphologies of the sol-gel film and TC4 matrix was observed by SEM(Scanning Electron Microscope),stereomicroscope,etc.The bonding strength between TC4 alloy coated with a sol-gel film after different natural oxidation times and the acrylic polyurethane primer was tested using the pull-off method.And the bonding strength between TC4 alloy coated with a sol-gel film after different natural oxidation times and the acrylic polyurethane primer before and after the 240 h neutral salt spray test was investigated by scratching method,and photographed under a stereomicroscope,and then the adhesion grade was evaluated.Finally,the influence mechanism of oxidation time on the film formation behavior and the film properties was proposed based on the results of XPS(X-ray Photoelectron Spectroscopy)and other experiments.The results indicated that in the range of 0-36 h,the natural oxidation time had little effect on the corrosion resistance of the oxide film on the surface of TC4 alloy.With the extension of natural oxidation time,the contact angle between the titanium alloy surface and sol-gel increased,and the contact angle increased from 4.5° in the test immediately after activation by acid washing to 44.3° in 36 h of natural oxidation.The adhesion work tended to decrease with the extension of the natural oxidation time,from 103.94 mJ/m2 after the activation to 89.33 mJ/m2 after natural oxidation for 36 h.The natural oxidation time had little effect on the bonding strength between TC4 alloy coated with a sol-gel film after different natural oxidation times and the acrylic polyurethane primer,and the bonding strength grades were all rated as grade 0.However,after the 240 h neutral salt spray test,the detached area of the acrylic polyurethane primer increased significantly.After pretreatment,the natural oxidation time was prolonged,and the hydroxyl(—OH)content on the surface of titanium alloy was reduced while the oxides content increased,which hindered the polycondensation degree between the sol-gel and the TC4 alloy matrix,and was not conducive to sol-gel film formation.When the film is in contact with aggressive media,corrosive ions penetrate into the pores at the interface between the sol-gel film and the TC4 alloy matrix,destroying the structure of the sol-gel film and leading to a large area of acrylic polyurethane primer peeling.关键词
钛合金/工序转移时间/自然氧化时间/溶胶凝胶/成膜行为/膜层性能Key words
titanium alloy/process transfer time/natural oxidation time/sol-gel/film-forming behavior/film properties分类
金属材料
