| Magnesium alloys have wonderful prospect for application in the automotive,aerospace,communications and portable microelectronics fields due to their high stiffness/weight ratio,good castability,good shock absorption,high heat conductivity and electrical conductivity.However,the magnesium alloys can easily be eroded by chloride ions for their active chemical properties and low corrosion resistances,which has become the bottleneck limiting its application.In recent years,The researchers found that:Layered double hydroxides?LDHs?has a unique layered structure and interlayer anion exchangeability,which can be used on the surface of magnesium alloys to reduce the contact between magnesium alloy and corrosive liquid,thereby effectively improving its corrosion resistance.In LDHs materials,the ZnAl-type LDHs materials are more prone to ion exchange reaction,they can be used as a container for corrosion inhibitors to improve the corrosion resistance of the magnesium alloys.Different anions intercalated into the layers of ZnAl-LDHs to control the LDHs of morphology,interlayer spacing and affect its corrosion resistance.Therefore,The ZnAl-LDHs films intercalated with inorganic anions(NO3-,Cl-,VO43-,PO43-and MoO42-)and organic anions?lauric acid?La?and aspartic acid?ASP??were prepared on magnesium alloy substrate.The effects of different anions on the morphology,structure and corrosion resistance of ZnAl-LDHs films were investigated by means of SEM,EDS,XRD,FTIR and electrochemical workstations.The main conclusions are listed as follows:?1?The ZnAl-NO3--LDHs films were prepared on AZ31 magnesium alloy by hydrothermal method.ZnAl-LDHs films intercalated with different anions(Cl-,VO43-,PO43-and MoO42-)were obtained by anion exchange.A uniform and dense nanoplates structure is formed,and the thickness of films intercalated with from NO3-,Cl-,PO43-,MoO42-and VO43-anion is gradually increased,and the thicker the films,the better it is to block the penetration of Cl-.?2?Polarization curves and EIS results show that the corrosion resistance of ZnAl-LDHs films with different anions is arranged in order as follows:ZnAl-VO43--LDHs>ZnAl-MoO42--LDHs>ZnAl-PO43--LDHs>ZnAl-Cl--LDHs>ZnAl-NO3--LDHs.Among them,The presence of Cl-in the ZnAl-Cl--LDHs films can reduce the penetration of external Cl-,which can effectively reduce the occurrence of corrosion.The ZnAl-LDHs films intercalated with PO43-,MoO42-and VO43-can effectively absorbing aggressive Cl-and releasing interlayer anions to reduce corrosion,it's corrosion resistance is better than ZnAl-Cl--LDHs.The VO43-containing ZnAl-LDHs possessing the largest basal spacing distances d?003?value and strongest ability to release anions and absorb chloride ions,and the corrosion current density(3.026×10-7 A/cm2)is two orders of magnitude lower than that of magnesium alloy substrate(7.482×10-5A/cm2),so ZnAl-VO43--LDHs films has the optimal corrosion resistance.?3?The ZnAl-LDHs films intercalated with ASP/La were situ prepared on magnesium alloy substrates by hydrothermal method.Both films were uniformly and densely grown on the surface of magnesium alloys.ZnAl-ASP-LDHs films possess the nanoplates structure,these nanoplates are perpendicular to magnesium alloy substrate.while the ZnAl-La-LDHs films presents an inclined interlaced nanoplates structure,this is more conducive to blocking the erosion of Cl-.The basal spacing distances of ZnAl-LDHs intercalated with La anion of the d?003?is much larger than that ASP anion containing ZnAl-LDHs,indicating that ZnAl-La-LDHs films have better absorption ability of Cl-.?4?The nanosheets on the surface of the ZnAl-ASP-LDHs films dissolve to form a dense protective layer,while the nanosheets on the surface of the ZnAl-La-LDHs film become more vertical,after etching.The corrosion current density(2.772×10-7 A/cm2)of ZnAl-La-LDHs films is better than that of ZnAl-ASP-LDHs films(3.933×10-7A/cm2),and both of the corrosion current density is higher than that of magnesium alloy substrate(7.482×10-5 A/cm2),indicating that the ZnAl-LDHs films intercalated with organic anions?ASP,La?can improve the corrosion resistance of magnesium alloy,and the corrosion resistance of ZnAl-La-LDHs films is better. |
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