The influence of NaCl and CO2 on the atmospheric corrosion of magnesium alloy AZ91

• The influence of NaCl and CO2 on the atmospheric corrosion of magnesium alloy AZ91 is studied in the laboratory. Samples were exposed under carefully controlled air and flow conditions; the relative humidity was 95%, the temperature was 22.0degreesC and the concentration of CO2 was <1 ppm or 350 ppm. Different amounts of sodium chloride (0-70 μg/cm(2)) were added before exposure. The corrosion products were analyzed by gravimetry, ion chromatography, X-ray diffraction and scanning electron microscopy. Mass gain and metal loss results are reported. The combination of high humidity and NaCl is very corrosive towards AZ91. However, the NaCl-induced corrosion is inhibited by ambient concentrations of CO2. Exposure in the absence of CO2 gives rise to heavy pitting, with brucite, Mg(OH)(2), being the dominant corrosion product. In the presence of CO2 a layer of hydrated magnesium hydroxy carbonate, Mg-5(CO3)(4)(OH)(2) &BULL; 5H(2)O forms. A tentative corrosion mechanism is presented that explains the behavior in the two environments.

Nyckelord

behavior

aluminum

tropics

microstructure

resistance

chloride

vietnam

zinc

mg

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