Effect Of Lanthanum And Cerium Mischmetal On Corrosion Resistance And Semiconducting Of AM60B Magnesium Alloy

In the modern metarials science,magnesium alloy have a rapid development and wide application due to its many excellent properties.However,magnesium has active chemical character and the magnesium oxide film product in the air is porous,unable to prevent the further oxidation suffciently.Compared with other metals,megnesium has the lowest standard potential,^-2.37V,and will be corroded for the sacrificial anodes corrosion in the sulotion.Poor corrosion resistance has become the main factors restricting the development of magnesium alloy.In this thesis,we study electrochemical behavior of magnesium alloy in NaCl solutions with different pH value and concentration.The corrosion current density of magnesium alloy is minimal 4.436μA·cm^-2 in 0.035%NaCl solution with PH=10.5,and maximal 84.34μA·cm^-2 in 3.5%NaCl with PH = 3.5.With the decrease of PH and the increase of the solution concentration,anode current density is increase and AM60B-MM corrosion potential is shifted to nagtive,and additionally,the capacitive reactance radius is increaseWe coat film in the surface of AM60B-MM magnesium alloy by using electrochemical convension mechanism with permanganate,molybdate and phytic acid,respectively.The coating process with all the three medium reduce the corrosion current density of AM60B-MM magnesium alloy.Among them,the corrosion current density with permanganate is lowest,22.823μA·cm^-2.The decrease of the corrosion current density indicates that the increasing capacitive reactance arc,low-frequency impedance modulus,and phase angle due to the formation of film with high resistance and large capacitance.The electrochemical property of AM60B-MM magnesium alloy is improved after the coating process.The slope of Mott-Schottky curve with the three medium（permanganate,molybdate and phytic acid）increases with the increasing electric potential in the region[^-2.2,-0.9]V under the fixed temperature,NaCl solution concentration and PH.The increase of the slope,corresponding to the decreases of the donor density ND and space charge layer width,as well as the negative shift of flat band potential,indicates the improment of alloy electrochemical property.The measurement on evolution of hydrogen gives the corrosion current density of AM60B-MM magnesium alloy after the coating process,0.953×10-9A/cm² for permanganate,2.034×10-9 A/cm² for molybdate,and 2.879×10-9A/cm² for phytic acid,all of which are drastically suppressed compared with those before the coating process.