| Magnesium alloys were easy to be corroded due to their active chemical properties.Magnesium alloys often required high corrosion protection costs,resulting in huge economic losses.The use of organic coatings with anti-corrosion function could be simple,fast and effective for corrosion protection.And organic coatings could greatly reduce the cost.The anti-corrosion effect of traditional organic coatings could be applied to shield the protected material from external contact.When the coating was damaged,corrosion intensification couldn't be stopped.It was very important to prepare organic anticorrosive coatings with good shielding property and corrosion inhibition.Microcapsule core corrosion inhibitor could effectively improve the corrosion inhibition of organic anticorrosive coatings.Cracks occured when the coating was damaged by external forces.Under the action of the stress at the crack tip,the microcapsule cracked and the core material was released.After the core material reacted with the magnesium alloy substrate,the product film was formed,which inhibited the further expansion of corrosion.On this basis,this paper first prepared 8HQ-PF microcapsule,and discussed the preparation process of microcapsule.Furthermore,the microcapsules and epoxy coatings were compounded to prepare microcapsule/epoxy composite coatings with good shielding property and corrosion inhibition.The effects of the mass fraction of curing agent and the mass fraction of microcapsules on the pencil hardness,adhesion and mechanical properties of composite coatings were discussed.And the influence of the microcapsule mass fraction on the corrosion resistance of the microcapsule/epoxy composite coating on the AZ91D magnesium alloy was studied.The main work and conclusions of the paper included:(1)Using high-efficiency corrosion inhibitor 8HQ as the capsule core and phenolic resin PF as the capsule wall,8HQ-PF microcapsules were prepared.Using laser particle size distribution analyzer,thermogravimetric and differential heat analyzer and other instruments to analyze the particle size distribution and core material content of the microcapsules,the best process was obtained.The results show that when the amount of emulsifier PVA was 5%,the stirring speed was 500 rpm,the core-to-wall ratio was 9:10,the acid dropping rate was 2.0 d/s,the temperature was 65?,and the phenol/formaldehyde molar ratio was 4:5,and the reaction time was 5 h,the microcapsule had the best performance,good spheroidization,good dispersibility.At the same time,the core material content was 41%,and the encapsulation efficiency was 87%.(2)Added 8HQ-PF microcapsules to epoxy coatings to prepare microcapsule/epoxy composite coatings,and study the effects of curing agent content and microcapsule content on the hardness,adhesion and mechanical properties of composite coatings.The results show that when the mass fraction of microcapsules was 4%,the performance of the microcapsule/epoxy composite coating was the best,the tensile strength was 12.0 MPa,the impact strength was 35.9 kJ/m2,the hardness was 6 H,the adhesion was 0 grade,and the gloss was 25.8.Compared with polyurethane coatings,epoxy coatings had a smooth surface without pores after curing,and had better shielding capabilities.(3)The 8HQ-PF microcapsule/epoxy composite coating was used for the surface protection of AZ91D magnesium alloy,and the anti-corrosion performance of the composite coating on the surface of AZ91D magnesium alloy was studied,and then the anti-corrosion mechanism was studied.The results show that when the microcapsule mass fraction was 4%?6%,the anticorrosion performance of the microcapsule-epoxy composite coating was the best.After the scratched AZ91D magnesium alloy was immersed in 3.5%NaCl solution for 72 h,the impedance value of the composite coating with 4%microcapsule content in the low frequency region was about 1986 ?/cm2,which was 6 times higher than that of the pure epoxy coating.The anti-corrosion mechanism was that after the microcapsule/epoxy composite coating on the surface of the AZ91D magnesium alloy was scratched,the microcapsule-coated corrosion inhibitor 8HQ was released.The corrosion inhibitor 8HQ reacted with magnesium to form a Mg(8HQ)2 film,which realized the anticorrosion effect of corrosion inhibition ability. |
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