The phosphated zinc layer was post-sealed with molybdate to obtain the composite coating without pores.The composition of the formed coating was investigated. The corrosion behavior of the coated samples was studied.T...The phosphated zinc layer was post-sealed with molybdate to obtain the composite coating without pores.The composition of the formed coating was investigated. The corrosion behavior of the coated samples was studied.The coated samples were first scratched and subsequently corroded in a neutral salt spray( NSS) chamber for 2-72 h; the microstructure of the corrosion products was analyzed via SEM and EDS; and the self-healing performance was discussed. The coating obtained contains Zn_3( PO_4)_2· 4H_2 O,Mo_2O_3 and MoO_4^(2-). The electrochemical impedance first increases and then decreases with the immersion time. However,after immersion for 6 days,it remains at about 10 kΩ·cm^2,much higher than the value for the single-treated samples without corrosion. Micro structural observations show that the corrosion products in scratch increase in size and finally cover the whole scratch completely. The initial corrosion products have high P,Mo and O contents but almost no Cl,while in later stages the first three components decrease and Cl increases. The corrosion products form a compact mass of needle-like crystals,effectively inhibiting zinc corrosion. The composite coating exhibits good self-healing.展开更多
基金Sponsored by the National Natural Science Foundation of China(Grant Nos.51408517 and 51578255)the Natural Science Foundation of Fujian Province(Grant No.2017J01489)
文摘The phosphated zinc layer was post-sealed with molybdate to obtain the composite coating without pores.The composition of the formed coating was investigated. The corrosion behavior of the coated samples was studied.The coated samples were first scratched and subsequently corroded in a neutral salt spray( NSS) chamber for 2-72 h; the microstructure of the corrosion products was analyzed via SEM and EDS; and the self-healing performance was discussed. The coating obtained contains Zn_3( PO_4)_2· 4H_2 O,Mo_2O_3 and MoO_4^(2-). The electrochemical impedance first increases and then decreases with the immersion time. However,after immersion for 6 days,it remains at about 10 kΩ·cm^2,much higher than the value for the single-treated samples without corrosion. Micro structural observations show that the corrosion products in scratch increase in size and finally cover the whole scratch completely. The initial corrosion products have high P,Mo and O contents but almost no Cl,while in later stages the first three components decrease and Cl increases. The corrosion products form a compact mass of needle-like crystals,effectively inhibiting zinc corrosion. The composite coating exhibits good self-healing.
