Corrosion behavior of flame-resistant Calcium-added Magnesium alloy in NaCl aqueous solution containing various anion species

Flame-resistant Ca-added Mg alloys are highly desirable as the materials for transport industry from viewpoints of the safety and lightweight. Recently, exposure tests of the Ca-added Mg alloys demonstrated that the anion species other than chloride ion, such as nitrate and sulfate ions, were present in the corrosion products formed on the Mg alloys. However, details of the corrosion behavior of the Ca-added Mg alloys have been not yet clarified. In this study, we aimed to investigate the corrosion behavior of the flame-resistant Ca-added Mg alloy in NaCl aqueous solution with and without sulfate ions by immersion testing. XRD and FT-IR measurements demonstrated that the corrosion products formed on the Ca-added Mg alloy AZX612 were composed of Mg(OH)₂, MgCO₃, and Mg-Al layered double hydroxide (LDH). Immersion tests in the corrosive solution revealed that the addition of SO₄^2- to NaCl promoted the formation of the of Mg(OH)₂. The dense layer of Mg(OH)₂ served as an protective film towards corrosive NaCl solution, thus resulted in decreasing the corrosion rate of the flame-resistant Ca-added Mg alloy.