Studying the anti-corrosive properties of a polyurethane coating on the AZ31 magnesium alloy via surface chemical modification by nano-conversion coatings based on praseodymium

This study is an investigation on the effects of chemical modification of magnesium alloy AZ31 surface by conversion coating e based on praseodymium on anti-corrosion performance of polyurethane coating. First, the results confirmed the forming of conversion coating on magnesium alloy. Then, different effective corrosion variables are analyzed by Electrochemical Impedance Spectroscopy (EIS) and the optimum data was achieved. Moreover, anti-corrosion performance of polyurethane coating was investigated via Electrochemical Impedance Spectroscopy (EIS), pull-off, and salt spray tests.
Thereupon PrCC is performed appropriate roughness on magnesium by formed oxide species Pr2O3, PrO2, Pr(OH)3 on magnesium substrate that is causing to enhanced roughness of substrate and caused of increased adhesion Polyurethane coatings. Its results in EIS analysis showed the increase of impedance  100000 Ω cm2 and phase angle of 80 degree in 6 even more 24 hour even though untreated  magnesium is impedance  150000 Ω cm2 and phase angle of 70 degree, and demonstrated that PrCC by creating barrier properties causing to impede and hindrance of corrosion electrolyte such as OH-, Cl- and other corrosion ingredients; however, gradually prolong time dipping in electrolyte, penetration of corrosion ingredients into interface of magnesium treated by PrCC and PU leading to blistering and completely delamination of coating after 240 hour. According to the results of the tests, an improvement in the corrosion resistance and increase in adhesion can be observed.