The Organizational Structure Of The Cold Spraying Al Composite Coating And Corrosion Behavior Research

With the rapid development of China's economy,and the mass construction of offshore steel structures such as port terminals and cross-sea bridges,a large number of metal materials have been put into use.The steel structures,being in contact with corrosive medium in the marine environment,are seriously eroded.Therefore,the service life is significantly decreased.In this paper,five Al composite coatings are prepared with cold spraying technology.In addition,this paper analyzes the mechanical properties and organizational structures of coatings,conducts research on corrosion behavior of coatings with electrochemical method,studies the corrosion mechanism of coatings,and analyzes mechanical properties and corrosion resistance of coatings.After studying the mechanical properties and organizational structures of five cold spraying coatings,the paper finds out that there are no obvious defects in both the surface and interface of coatings,and the compactness is good.The hardness of Al-25%Al₂O₃ coatings can reach more than 980 microns while the hardness of other four coatings can reach more than 290 microns.The hardness of five coatings are all above 59.6 HV,with the hardness of Al-25%Zn-25%Al₂O₃ coating reaching over 100 HV.The porosity of five coatings are lower than 2.44%,and the porosity of Al-50%Zn coating is only 1.64%.The porosity of Al-50%Zn-25%Al₂O₃ coating,after adding alumina powder,reduces significantly to just 1.13%,the lowest among the five.The porosity of Al-50%Zn and Al-50%Zn-25%Al₂O₃ coatings are significantly lower than that of Al-25%Zn and Al-25%Zn-25%Al₂O₃ coatings,showing that raising the proportion of zinc powder can reduce the porosity of coatings.This paper studies the corrosion resistance of five cold spraying coatings and finds that the ecorr of Al-25%Zn-25%Al₂O₃ and Al-50%Zn-25%Al₂O₃ coatings at the late stage of soaking tends to stabilize at-0.98 V,and the corrosion resistance is better than other AI composite coatings.After 336 h of soaking,the corrosion current density of Al-25%Al₂O₃,Al-25%Zn-25%Al₂O₃ and Al-50%Zn-25%Al₂O₃ coatings are 0.35?A/cm2,26.41?A/cm2 and 15.29?A/cm2 respectively.Generally speaking,the current density of five coatings at the late stage of soaking basically tend to stabilize,the corrosion resistance is good,and the protective ability is strengthening gradually.The capacity reactance arc in impedance spectrum of Al-25%Al₂O₃ coating presents a trend of first increase and then decrease.In the early stage of soaking,there is a high frequency capacity reactance arc and a low frequency line.After 336 h of soaking,there is an obvious low frequency line.In the soaking process of Al-25%Zn and Al-50%Zn coatings,there is only one capacity reactance arc,and then the radius of capacity reactance arc shows a rising tendency.In the early stage of soaking of Al-25%Zn-25%Al₂O₃ coating,there is a high frequency capacity reactance arc and a low frequency line,and the radius of the capacity reactance arc presents a rising tendency.After 168 h,there is a low frequency line.As for Al-50%Zn-25%Al₂O₃ coating,there is an obvious low frequency diffusion phenomenon after 528 h.Over all,the corrosion resistance of five coatings in the late stage is gradually increasing,the radius of capacity reactance arc of Al-25%Al₂O₃ is the biggest,and the corrosion resistance is the best.After 24 h of soaking,there is conspicuous passive region in Al-25%Al₂O₃ coating.After 528 h,the polarizability presents a rising tendency,the changing trend of coating's polarization curve is relatively stable,and the protective ability in the late stage of soaking gradually increases.There is no conspicuous passive region in the anode region of Al-25%Zn and Al-50%Zn,the change law of polarization curve is relatively stable,and the polarizability in the late stage of soaking presents a risng tendency.In the whole soaking process,the ecorr of Al-25%Zn-25%Al₂O₃ coating and Al-50%Zn-25%Al₂O₃ coating stabilizes at-0.95 V to-1.0V.After 96 h of soaking,there is passive region.The ecorr increases as electric current increases,and the polarizability is gradually presenting a rising tendency.In the late stage of soaking,the corrosion resistance of two coatings gradually increases,and the anti-corrosion effect is good.Comparing two sets of coatings as Al-25%Zn and Al-25%Zn-25%Al₂O₃,Al-50%Zn and Al-50%Zn-25%Al₂O₃,the paper finds that adding Al₂O₃ power doesn't have much influence on the polarization curve of soaking process of each coating.