Corrosion of magnesium Mg alloys during field exposure

6 Corrosion of magnesium (Mg) alloys during field exposure 

Some corrosion rates of Mg alloys at different field exposure sites given in the literature (25-27) are displayed in Table 7.2. The highest corrosion rate, 8.8 (J,m/year, is shown for the AM50 alloy exposed in marine environment for one year, i.e. 2005-05-31 to 2006-05-23. The corrosion rate of AZ91D, measured in J,m/year, is after 12 months of exposure 4.2, 2.2 and 1.8 for the marine, rural and nrban exposures, respectively. The weight loss of the Mg alloys is linear with time (25). This was also seen in the laboratory (22) and has been reported in the literature (26). The weight of the field-exposed 

Magnesium alloy AZ91A-T6 Magnesium alloy AZ61X. 

1 A matrix of corrosion panels exposed under a truck in Dubai. 

The reaction sequence of the formation of corrosion products on NaCl-contaminated AZ91 under laboratory conditions was studied by the authors of this chapter (22). As seen from reaction 4.4 above, MgOH2 is the overall corrosion product and is also the main corrosion product in bulk solution (31). However, brucite is stable only at low CO2 partial pressures (32). At the levels of CO2 found in ordinary atmosphere, bmcite will react directly with CO2 to form magnesite. The reaction then becomes  

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