Effective inhibition of magnesium-lithium-aluminum alloys corrosion by sodium molybdate

Magnesium alloys are widely applied as structural materials in aerospace and automotive industries due to their light weight, excellent formability, high specific strength, and damping characteristics. Lithium has been added to magnesium alloys to improve ductility and reduce weight. On the other hand, the addition of lithium decreases their strength and, often, corrosion resistance. The present work aims to study the effect of Na₂MoO₄ on the corrosion inhibition of magnesium-lithium-aluminum alloys Mg–xLi–3Al (x = 4–15%) in 0.05 M NaCl solutions. The mechanism of corrosion inhibition using aqueous molybdate was characterized by the electrochemical measurements, hydrogen evolution, Raman spectroscopy, and SEM-EDX. Electrochemical measurements showed that the addition of 10 to 150 mM of molybdate inhibitor in 0.05 NaCl solutions results in the inhibition efficiency from 64 to 80 %, respectively. Raman results showed that the addition of Na₂MoO₄ inhibitor leads to the formation of a passive layer on the surface. In turn, the α+β MgLi phases present in the alloys are the centers of the surface passivation through the formation of a passive layer on the surface. The passive layer consists of Mg(OH)₂, crystalline molybdates, and mixed-valence molybdenum oxides. Concluding, molybdate is a highly-effective corrosion inhibitor of magnesium-lithium-aluminum alloys.