Study On The Performance Of Chromium-free Zinc-Aluminum Coating Containing Nano-Materials

Dacromet coating has been widely used in high-speed railways,automobile industry,construction and other fields because of its excellent corrosion resistance.However,its application has been strictly restricted in recent years because of the Cr⁶⁺contained in the coating.The development of chromium-free zinc-aluminum coating becomes an inevitable trend.But the corrosion resistance,hardness and wear resistance of chromium-free zinc-aluminum coating need to be further improved.In this paper,the affecting rule and mechanism of nano-fillers on the performance of chromium-free zinc-aluminum coating have been studied.In this paper,the influences of zinc-aluminum powder content,MWCNTs and MWCNTs-nano-Zn O composite fillers on the morphology,phase,water contact angle,binding force and hardness of chromium-free zinc-aluminum coating were studied respectively.The research results showed that（1）the optimal content of zinc aluminum powder was 20%.Under this condition,the macroscopic surface of the coating was smooth and flat,with uniform thickness,which was between 33 and 35μm.The phases in the coating were mainly Zn,Al and Zn O.The water contact angle was 37.9°,and the adhesion was ISO-1 level.（2）The surface morphology and phase of the coating were not greatly affected by MWCNTs.The water contact angle of the coating was greatly affected by MWCNTs.When 0.3%of MWCNTs was added,the water contact angle of the coating had a maximum value of 72.4°.The adhesion of the coating was ISO-1 level.（3）The phases of the MWCNTs-nano-Zn O composite coating were Zn,Al and Zn O,and the Zn O diffraction peak intensity was 3 times that of no nano-Zn O coating.The hardness of the coating was significantly improved as the addition of nano-Zn O increased.When the addition was 0.7%,the hardness of the coating was 156.5HV0.1,which was 50.3%higher than that of the coating without nano-particles.In this paper,the influences of zinc-aluminum powder content,MWCNTs and MWCNTs-nano-Zn O composite filler on the corrosion resistance and wear resistance of the coating were also studied.The research results showed that（1）The coating impedance modulus with the optimal zinc-aluminum powder content was 361.3Ω·cm²,and the self-corrosion current density was 2.072×10^-4A/cm².（2）As the MWCNTs content increased,the coating impedance modulus first increased and then decreased,while the trend of self-corrosion current density was opposite.When the addition amount was 0.3%,the coating impedance modulus was1.05×10³Ω·cm²,the self-corrosion current density was 2.019×10^-5A/cm².（3）with the increase of nano-Zn O content,the coating impedance modulus first increased and then decreased,and the self-corrosion current density first decreased and then increased.When 0.5%nano-Zn O was added,the coating impedance modulus value was 1.37×10⁴Ω·cm²,and the self-corrosion current density was 4.755×10^-6A/cm².（4）For the mechanism of nano-fillers affecting the corrosion resistance of the coating,MWCNTs enhanced the shielding performance of the coating,and increased the electrical connection between the zinc and aluminum powders,which improved the cathodic protection performance of the coating.Nano-Zn O filled the pores of the coating,improving the shielding performance of the coating.（5）The friction coefficient of the coating without nano-filler was 0.84,and the friction coefficient of the coating with 0.3%MWCNTs was 0.89.The friction coefficient of the coating was significantly reduced by nano-Zn O addition,the friction coefficient first decreased and then increased with the addition of nano-Zn O.When the addition content was 0.3%,the friction coefficient of the coating was only 0.67,which was 20.2%lower than that of the coating without nanoparticles addition.