Plasma electrolytic oxidation(PEO)is commonly employed to enhance the corrosion resistance of magnesium and its alloys.However,the formation of pores during this process can compromise the corrosion resistance of the ...Plasma electrolytic oxidation(PEO)is commonly employed to enhance the corrosion resistance of magnesium and its alloys.However,the formation of pores during this process can compromise the corrosion resistance of the PEO coating.In this study,the PEO coating on an AZ91D magnesium alloy was subjected to post-treatment in Cr_(2)(SO_(4))_(3)solutions to further improve its corrosion resistance.The structural characteristics and corrosion resistance(evaluated in a 3.5%NaCl solution)after Cr_(2)(SO_(4))_(3)sealing treatment were investigated.The results revealed that,in the acidic sealing solution,oxides such as MgO and Mg_(2)SiO_(4)in the PEO coating were dissolved,resulting in a local increase in pH.This pH increase promoted the precipitation of Cr2O_(3)and Cr(OH)_(3),which filled the micropores of the PEO coating.As the sealing time progressed,an outer layer containing Cr2O_(3)and Cr(OH)_(3)formed on the coating surface,enhancing the compactness of the PEO coating.The resistance of the PEO coating increased from 5.13×10^(5)Ωcm^(2)to 1.56×10^(6)Ωcm^(2)after sealing for 60 min.The average hydrogen evolution volume decreased from 21.77 ml/cm^(2) to 0.2 ml/cm^(2)(after immersion in 3.5%NaCl solution for 7 days);and no visible corrosion products were detected on the surface of the sealed samples after immersion for 100 h.These findings suggest that trivalent chromium sealing is a promising method that can effectively enhance the corrosion resistance of PEO coatings on magnesium alloys.展开更多
Trivalent chromium process(TCP)conversion coating has been widely used on aluminum alloys due to its high corrosion resistance and relatively low toxicity.Much work has indicated that the corrosion resistance of TCP c...Trivalent chromium process(TCP)conversion coating has been widely used on aluminum alloys due to its high corrosion resistance and relatively low toxicity.Much work has indicated that the corrosion resistance of TCP conversion coating is highly dependent of aluminum alloy type,but the associated mechanism is still not clear.In this paper,based on a Cr-Zr-Ti conversion solution,the structure and corrosion resistance of the TCP coating on four typical aluminum alloys,namely 2024-T351,7050-T7451,6061-T6 and 5056-H18,have been investigated.It was found that the TCP coatings formed on 5056 and 6061 alloys showed higher corrosion resistance than those formed on 2024 and 7050 alloys,and the corrosion resistance was negatively related to the amount of Cu in the coating.Mg and Zn were present as oxides and hydroxides in the coating,beneficial to the compactness of the TCP coating.Compared with Cu,Mg and Zn,Si had less effect on the structure and corrosion resistance of the coating.It is suggested that the incorporation of the alloying elements from the alloy substrate into the TCP coating have contributed greatly to different structure and corrosion resistance of the TCP coatings formed on different aluminum alloys.展开更多
基金supported by the Chongqing Natural Science Foundation(CSTB2022NSCQ-MSX0326)Chongqing Talent Plan:Leading Talents in Innovation and Entrepreneurship(CQYC201903051)+1 种基金Science and Technology Research Program of Chongqing Municipal Education Commission,China(Grant No.KJQN202301138)the Scientific Research Foundation of Chongqing University of Technology,China(Grant No.2023ZDZ004).
文摘Plasma electrolytic oxidation(PEO)is commonly employed to enhance the corrosion resistance of magnesium and its alloys.However,the formation of pores during this process can compromise the corrosion resistance of the PEO coating.In this study,the PEO coating on an AZ91D magnesium alloy was subjected to post-treatment in Cr_(2)(SO_(4))_(3)solutions to further improve its corrosion resistance.The structural characteristics and corrosion resistance(evaluated in a 3.5%NaCl solution)after Cr_(2)(SO_(4))_(3)sealing treatment were investigated.The results revealed that,in the acidic sealing solution,oxides such as MgO and Mg_(2)SiO_(4)in the PEO coating were dissolved,resulting in a local increase in pH.This pH increase promoted the precipitation of Cr2O_(3)and Cr(OH)_(3),which filled the micropores of the PEO coating.As the sealing time progressed,an outer layer containing Cr2O_(3)and Cr(OH)_(3)formed on the coating surface,enhancing the compactness of the PEO coating.The resistance of the PEO coating increased from 5.13×10^(5)Ωcm^(2)to 1.56×10^(6)Ωcm^(2)after sealing for 60 min.The average hydrogen evolution volume decreased from 21.77 ml/cm^(2) to 0.2 ml/cm^(2)(after immersion in 3.5%NaCl solution for 7 days);and no visible corrosion products were detected on the surface of the sealed samples after immersion for 100 h.These findings suggest that trivalent chromium sealing is a promising method that can effectively enhance the corrosion resistance of PEO coatings on magnesium alloys.
基金Chongqing Natural Science Foundation(CSTB2022NSCQ-MSX0326)Chongqing Talent Plan:Leading Talents in Innovation and Entrepreneurship(CQYC201903051)University Innovation Research Group of Chongqing(CXQT20023).
文摘Trivalent chromium process(TCP)conversion coating has been widely used on aluminum alloys due to its high corrosion resistance and relatively low toxicity.Much work has indicated that the corrosion resistance of TCP conversion coating is highly dependent of aluminum alloy type,but the associated mechanism is still not clear.In this paper,based on a Cr-Zr-Ti conversion solution,the structure and corrosion resistance of the TCP coating on four typical aluminum alloys,namely 2024-T351,7050-T7451,6061-T6 and 5056-H18,have been investigated.It was found that the TCP coatings formed on 5056 and 6061 alloys showed higher corrosion resistance than those formed on 2024 and 7050 alloys,and the corrosion resistance was negatively related to the amount of Cu in the coating.Mg and Zn were present as oxides and hydroxides in the coating,beneficial to the compactness of the TCP coating.Compared with Cu,Mg and Zn,Si had less effect on the structure and corrosion resistance of the coating.It is suggested that the incorporation of the alloying elements from the alloy substrate into the TCP coating have contributed greatly to different structure and corrosion resistance of the TCP coatings formed on different aluminum alloys.
