| TC4 titanium alloy has attracted many interests and has been applied in aerospace field,owing to its light weight and high strength.However,when the alloy is used as a fastener in contact with aluminum skin,it will not only cause galvanic corrosion,but also led to stress corrosion and crevice corrosion,which shortens the service life of structural components.In order to effectively improve the contact corrosion of titanium/aluminum alloy,in this paper,we began to study the main factors of effect corrosion,Zn-Al alloy coating was prepared on the surface of TC4 titanium alloy based on the chromium-free dacrometal technology,and the protective mechanism of the coating was systematically analyzed.In this paper,16 groups of orthogonal experiments were designed according to the general formula of chromium-free Zn-Al alloy coating.Through the comprehensive consideration of the appearance,adhesion and corrosion resistance of the as-prepared 16 coating samples,the best formula of coating was obtained.And then the comprehensive performance of the coating prepared for the best formulation was tested.Finally,the protective effect of the Zn-Al alloy coating on the contact test of Ti/Al alloys were studied by immersing corrosion test,the neutral salt-spray test and electrochemical test.At the same time,the corrosion morphology and composition of the sample were also analysised by SEM,EDS and XRD.The results show that:(1)The optimization formulation was as follows: Zn-A1 alloy powder(7.50g),binder(0.60g),phosphorus sodium molybdate(0.60g),Tween-20(0.80g),BYK-346 solution(3.0g),Degussa 901 W defoamer(0.03g),SN-Thickener 621 N leveling agent(0.06g)and Degussa A200(0.1g),respectively,the rest was deionized water.(2)When the coating thickness was about 35?m and its hardness was about 3B,the adhesion was also good,which satisfied the application requirement of the chromium-free Zn-Al alloy coating.(3)The aluminum alloy of the Ti/Al alloys couples was more serious corrosion than the aluminum alloy of the coating/Al alloys couples.Among them,the self-corrosion potential between the coating sample and aluminum alloy was about 315 mV which was lower than Ecorr of the Ti/Al alloys couples,the open circuit potential was 244 mV lower,and the potential of the coating sample was lower than that of the aluminum alloy.The results show that the existence of the coating not only can reduce the potential difference between titanium alloy and aluminum alloys,to decrease the current density of the couples,but also to make the two poles of the couples occur reversed phenomenon,that is,the previously corroded aluminum alloy anode was transformed into a protected cathode.(4)Titanium alloy of the coating/Al alloys couples have not been seriously corroded,which shows that the coating has a protective effect to the titanium alloy,and also has a certain resistance to corrosion itself. |
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