Corrosion inhibition of rapidly solidified Mg-3% Zn-15% Al magnesium alloy with sodium carboxylates

The ability of sodium linear-saturated carboxylates to protect magnesium alloys against aqueous corrosion was characterized. Electrochemical measurements of polarization resistance (R-p) and corrosion current I-corr showed the inhibition efficiency of these compounds is a function of their concentration and of the length of the aliphatic chain In every case studied, the efficiency increased with immersion time. At pH 8, the best inhibiting behavior was observed with 0.05 M sodium undecanoate. The potential-pH diagram of magnesium in an aqueous solution containing undecanoate anions was generated based upon the solubility determined for magnesium undecanoate (Mg[CH3(CH2)(9)COO](2)). According to this diagram, the very low corrosion rate was suspected to result from formation of Mg(CH3[CH2](9)COO)(2). Infrared spectrometry carried out on both the synthesized magnesium carboxylate and the product from the magnesium alloy surface after inhibitive treatment confirmed this hypothesis.