Magnesium and its alloys have found a variety of industrial applications. They are emerging to be one of the most basic types of choice for light structural and constructional materials. With a density of 1.7 g/cm3, it is easy to see why magnesium is attractive in automotive and aerospace industries. Unfortunately, bare magnesium alloys corrode rapidly when subjected to industrial atmosphere exposure and other severe corrosion environment, unless the alloy surface is properly treated and protected. Tables 1 and 2 indicate that magnesium has the lowest density among the light metal materials but the most active electrochemical property as compared with other typical structural alloys. Therefore, the competitiveness of magnesium alloys in industrial applications much relies on the surface treatment technologies to improve the resistance against oxidation or corrosion. Now the application of magnesium alloys is expanding, and they have been ranked the third most commonly used structural metals, following steel and aluminum alloys. This should be attributed to the development of effective and reliable surface treatment technologies, as well as a comprehensive understanding on the protection scheme of selecting appropriate surface treatment methods (Gray and Luan 2002; Chen et al. 2011a; Avedesian and Baker 1999; Kainer and Kaiser 2003; Friedrich and Mordike 2006; Hawkins 1993; Hillis 2005).

An optimal protection scheme provides magnesium alloys with reasonable and adequate resistance against corrosion and avoids unnecessary cost. Standard practices for preparation of magnesium alloy surfaces for moderate to severe environment cover two classes of treatment, as shown below (ASTM D1732 2007).

Recommended standard for moderate environment
Cleaning – chemical conversion coating – primer – top paint
Recommended standard for severe environment
Cleaning – anodizing – sealing – primer – top paint

The chart in Fig. 1 demonstrates a protection scheme of surface treatment sequences for magnesium alloys according to different classes of surface treatment. Generally, chemical conversion coating is adequate for moderate protection scheme, while anodizing and sealing are recommended for severely corrosive environment. Details of each step will be discussed in the next sections.