| The scaly zinc-aluminum alloy epoxy coating has good corrosion resistance due to the combination of the cathodic protection of zinc sacrificial anode and the physical shielding effect of sealing of aluminum and resin-based fillers.It has important potential applications in corrosion protection of steel.However,due to the imperfection of surface pretreatment in the actual construction process,its corrosion resistance and mechanical properties deteriorate.In view of the above problems,the effects of different pretreatment processes on the adhesion,corrosion resistance,friction and wear properties of the coatings were studied.At the same time,the corrosion of the coating in the atmospheric and soil environment was studied,and the corrosion resistance mechanism of the coating was further investigated.In this paper,different pretreatment coatings were prepared by air spraying.The corrosion resistance of scaly Zn-Al alloy epoxy coatings with different pretreatment processes was compared by electrochemical method combined with salt spray corrosion test.The microstructure and composition of the coatings were analyzed by SEM,EDS and XRD,and the mechanical properties of the coatings were characterized by common mechanical properties test methods.The corrosion of the coatings in real environment and simulated real environment was studied,and the corrosion products were analyzed,and the corrosion mechanism was studied in this topic.The results show that the surface of hot sprayed Zn-Al alloy coating was smooth and flat without any defects such as fine lines and bulging.But the Zn-50Al alloy coating has brighter color and less surface defects compared with Zn-15Al alloy coating.The microstructure of the two kinds of coatings was uniform and compact,and the coating was covered on the surface with lamellar structure,which can hinder the invasion of corrosive medium effectively.In salt spray atmosphere,the corrosion mechanism of Zn-15Al is mainly the self-sealing effect of zinc corrosion products,while the corrosion mechanism of Zn-50Al is mainly the shielding effect of aluminum oxide.With the increase of aluminum content in the coating,the polarization potential is moving forward,and the corrosion tendency decreases.The analysis of the coating structure showed that the scaly alloy powder on the surface of the coating was staggered and stacked in parallel,with a thickness of about 45?m,and there were no obvious defects inside.The XRD test showed that the main components of the coating were zinc-rich phase,aluminum-rich phase and Al0.403Zn0.597.597 phase.The adhesion of fully pretreated coating was 14.22 MPa,which is 68.5%higher than that of unpretreated cold rolled steel coating.The average porosity of fully pretreated coating was 1.67%,which is much smaller than that of untreated cold rolled steel coating?10.08%?,shot peening coating?7.81%?and alkali degreasing coating?4.59%?.The scratch hardness of the coating prepared by four different pretreatment processes can reach 5H or above with little difference.The adhesion and porosity of the fully pretreated coating are superior to those of the coating which has not been adequately pretreated.The surface of the fully pretreated coating is relatively flat,and the friction coefficient and wear loss are the smallest compared with other coatings.The corrosion resistance of fully pretreated coatings is much better than that of the three kinds of coatings which are not fully pretreated in both hot and humid conditions and simulated seawater.The corrosion current of fully pretreated coatings is the smallest,the polarization resistance is the largest and the protective efficiency of coatings is the highest,and the corrosion resistance of fully pretreated coatings is the strongest.Both the intact coating and the artificial scratch coating provide effective sacrificial anodic protection for the Q235 steel substrate.The results of electrochemical impedance spectroscopy?EIS?show that the intact coating relies on its good physical shielding effect at the initial stage of corrosion,the good cathodic protection of sacrificial anode at the middle stage of corrosion and the self-repairing effect at the later stage of corrosion to protect the substrate.Chemical corrosion is the main type of coating in indoor environment.In the outdoor environment,due to sunlight,SO2 gas in the air,and condensation of moisture due to capillary characteristics,corrosion at the edges is critical.After 6 months of corrosion in soil,the corrosion rate slowed down due to the filling and accumulation of corrosion products.It is easier for the coating to fail in strong alkali solution than in strong acid solution,and the strong alkali solution has a strong osmotic action and participates in the reaction inside the coating. |
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