The Research On Preparation And Corrosion Behavior Of Passive Film On B30 Cu-Ni Alloy

Copper-nickel alloy can form dense oxide film under the condition of long-term slow scouring clean seawater,which has excellent erosion and corrosion resistance.However,in recent years,many corrosion failure behaviors of copper nickel alloy pipeline have been found in the process of extensive using,such as pitting corrosion and other failure behaviors at the welding position of seawater pipeline,which may be related to the residual stress produced in the welding process.The formation of erosion resistant dense oxide film usually takes several months and requires pre passivation treatment.The passivation film can play a certain protective role in the early stage of pipeline erosion.Benzotriazole（BTA）,as a special corrosion inhibitor for copper alloy,is used as the basic system of passivation film-forming in this paper.The compound system can be formed by adding modifier to the basic system.This paper studied the passivation pretreatment and the improvement of passivation process parameters,also explored the effects of pretreatment and passivation process on the component structure and performance of passivation film.In terms of pretreatment:it was found that the pickling effect of different acids was different,and hydrochloric acid pickling effect was the best.Hydrogen peroxide activation treatment can improve the film quality.After mechanical sandblasting,the corrosion resistance of the sample was improved.The surface stress distribution was uniform after sandblasting.The X-ray diffraction results showed that the surface lattice was distorted after sandblasting.The scanning photos showed that the surface after sandblasting was a mesoscopic structure,which had corrosion inhibition effect.The polished surface was even,the open circuit potential was more stable in electrochemical test,and the passivation range was large and flat.In passivation process,the film formation of BTA basic system was better than that of B30alloy;BTA had synergistic effect with additives sodium molybdate（90 mg/L）,sodium tungstate（100 mg/L）and aminotriazole（1g/L）.The compound system composed of an appropriate amount of modifier and BTA was better than the basic system.In a certain range,the corrosion resistance of passive film increased with the increase of passivation temperature.The passivation time at room temperature was more than 3h,and prolonging the passivation time had little effect on the corrosion resistance of the passivation film;The passivation time at high temperature can be shortened to 40 min,and the corrosion resistance was better than that at room temperature.The composition and microstructure of primary oxide film and artificial passive film were studied.The surface of the film was mainly composed of copper and nickel oxides and Cu-BTA,Ni-BTA complexes.The proportion of oxides in the film-forming components at high temperature was higher,and the proportion of hydroxides in the film-forming components at room temperature was higher;All modifiers were involved in film formation.The results showed that the thickness of the film was about 10-20 nm,and the film was uniform and amorphous.Performance research:M-S test results showed that the high-temperature films were P-type and N-type,and the other films were P-type semiconductors;Among all passivation system,BTA-Na₂Mo O₄ passivate in 60°C had the least ion adsorption;which also had best certain self-healing properties.The long-term immersion impedance showed that the protection of artificial passive film was better than that of natural oxide film.