Research On Corrosion Resistance Of Aluminum And Aluminum Base Composite Coating To Cast Iron

Aluminum-based composite coatings(especially Al/Al2O3 composite coatings)have the advantages of excellent corrosion resistance,high hardness,easy recycling,etc.,and have broad application prospects and development potential in exterior coatings such as equipment.Electrodeposited aluminum and its composite coatings in ionic liquids have become a research hotspot in recent years due to low energy consumption and high efficiency.In this paper,AlCl3-EMIC(1-ethyl-3methylimidazole chloride)and ionic liquid added with nano α-A2O3 particles are used to study the properties of aluminum and Al/Al2O3 composite coatings on the surface of cast iron.Cyclic voltammetry and chronoamperometry were used to study the electrode process of coating deposition,and the effects of constant current density,deposition time,and deposition temperature on coating preparation and corrosion resistance were investigated.The study found that:(1)In AlCl3-EMIC ionic liquid,the aluminum deposition process on the surface of cast iron is controlled by diffusion and mass transfer,which is a quasireversible process;the aluminum nucleation growth on the cast iron electrode conforms to the three-dimensional instantaneous nucleation mechanism of diffusion-controlled growth;In the AlCl3-EMIC ionic liquid with α-Al2O3 particles,due to the presence of α-Al2O3,the precipitation potential of aluminum shifts positively;from the positive shift of-0.075 V when it is not added to about-0.05 V,the deposition of aluminum is relatively easier.(2)With the increase of current density,the crystal growth of aluminum coating changes from the preferred orientation of(200)plane to the random orientation of(200)(111)plane,and the grain size gradually decreases,the gap between the grains becomes smaller,and the corrosion resistance of cast iron is improved.When the current density reaches 30 mA/cm2,the coating self-corrosion current density is reduced by an order of magnitude.(3)Prolonging the deposition time can increase the thickness of the coating,but it also leads to the change of the preferred grain orientation from(200)to(111),the increase of grain size and the increase of the gap between grains,which is not conducive to the improvement of the corrosion resistance of cast iron.When the deposition time is 20 min,the grain size is small and the corrosion resistance is good,which is the best deposition time.(4)Although the increase of deposition temperature enhanced the ion transport rate and made the crystal faces change from the preferred orientation of(200)to the random growth of(200)(111),the corrosion resistance of the coating decreased with the increase of grain size and the increase of the gap between grains.When the deposition temperature is 20℃,the self-corrosion current density of the coating decreases by nearly two orders of magnitude.(5)The presence of α-Al2O3 made the coatings smaller and denser.Compared with the pure aluminum coating,the self-etching current density of the composite coating decreases by another order of magnitude.