Effect of the Surface Film Formed by Hydrogen Charging on the Corrosion Behavior of an As-Cast Mg–8%Li (in wt. %) Alloy

Abstract

In this study, the effect of electrochemical hydrogen charging on the corrosion behavior of an as-cast Mg–8%Li alloy was investigated. It was revealed that after being cathodically hydrogen charged in a 0.1 M NaCl solution at a constant current density of 50 mA/cm2 for 3 h, a product film with an average thickness of 20 μm was formed in the α-Mg phase, whilst the average thickness of the product film being formed in the β-Li phase was 6 μm. When the charging time was prolonged to 18 h, the thicknesses of the product films being formed on the α-Mg and β-Li phases were increased to 75 and 20 μm, respectively. The results of the grazing incidence X-ray diffraction (GIXRD) testing showed that the product films of the differently charged samples mainly consisted of Mg(OH)2, LiOH and Li2CO3. The formed product films on the two matrix phases were dense and could hinder the erosion of Cl− in a solution, and hence improved the corrosion resistance of the alloy. After being hydrogen charged for 3 h, the charge-transfer resistance (Rct) value of the alloy was increased from 527 to 1219 Ω·cm2. However, when the hydrogen charging time was prolonged to 18 h, the Rct was slightly reduced to 1039 Ω·cm2 due to the cracking of the surface product films and the interfacial cracking of the film/substrate matrix.