Influence of Uric Acid on the Corrosion Behavior of AZ31 Magnesium Alloy in Simulated Body Fluid

The action mechanism of uric acid, C₅H₄N₄O₃ (UA), and the effect of its concentration (0, 100, 416 and 500 μM) on the corrosion behavior of AZ31 Mg alloy in simulated body fluid were unmasked using scanning electron microscopy, x-ray diffraction, Raman, x-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, potentiostatic polarization, potentiodynamic polarization, and hydrogen evolution tests. It was shown that UA was initially dissociated into (C₅H₄N₄O₃)⁻ (UA⁻) and precipitated as (C₅H₄N₄O₃)₂Mg ((UA⁻)₂Mg). With the generation of (UA⁻)₂Mg, hydroxyapatite (HA) was continuously formed, enhancing the corrosion resistance of AZ31 Mg alloy. Subsequently, UA⁻ was transformed into C₅H₂N₄O₃ and chelated with Ca in HA as Ca(C₅H₂N₄O₃), resulting in a loss of HA and undermining the corrosion resistance of AZ31 Mg alloy. UA inhibited the corrosion of AZ31 Mg alloy with an optimal concentration of 416 μM. The inhibition of UA on the corrosion of AZ31 Mg alloy was closely related with the content of (UA^-)₂ Mg, Mg₃(PO₄)₂, and Mg(OH)₂ in the corrosion products.