Corrosion resistance of in-situ Mg-Al hydrotalcite conversion film on AZ31 magnesium alloy by one-step formation

In situ growth of nano-sized layered double hydroxides (LDH) conversion film on AZ31 alloy was synthesized by a urea hydrolysis method. The formation mechanism of the film was proposed. Firstly, the dissolved Mg2+ ions deposited into a precursor film consisted of MgCO3 and Mg-5(CO3)(4)(OH)(2)center dot 4H(2)O; secondly, the precursor translated into the crystalline Mg(OH)(2) in alkaline conditions; finally, the Mg2+ ions in Mg(OH)(2) were replaced by Al3+ ions, Mg(OH)(2) translated into the more stable LDH structure, simultaneously, the OH-ions in the interlayer were exchanged by 2CO(3), thus led to the formation of the LDH (Mg6Al2(OH)(16)CO3 center dot 4H(2)O) film. The results indicated that the LDH film characterized by interlocking plate-like nanostructures and ion-exchange ability significantly improved the corrosion resistance of the AZ31 Mg alloy.