Environmental Friendly Corrosion Inhibitors for Magnesium Alloys

Abstract

Magnesium is an important engineering material because of its light weight and excellent properties. Its density is 1.74 g⋅cm-3, only 2/3 that of aluminum and 1/4 that of iron. Moreover, it also has many advantageous properties such as good castability, hot formability, excellent machinability, good electromagnetic shielding characteristics, good biocompatibility, and recyclability (Cao et al, 2006; Staiger et al, 2006). Therefore, magnesium and its alloys have the potential to replace steel and aluminum in many applications. They have already been used in aerospace, aircraft, automotive, mobile electronics, biomaterials and other fields (Zhang & Zhang, 2004). However, there are some challenges for applications of magnesium and its alloys in a larger scale. The most important one is improving their poor corrosion resistance. Magnesium is a very active metal, and the standard potential of Mg2+/Mg is -2.356V (vs. N.H.E. at 25°C) (Bard & Faulkner, 2001). Therefore, magnesium and its alloys are extremely susceptible to corrosion, which can cause the decreased mechanical stability and unattractive appearance (Gray & Luan, 2002). To protect magnesium and its alloys from being corroded, the following techniques are frequently used (Zhang & Zhang, 2004): Conversion surface treatments, as chromating, phosphating, etc., Anodizing, Electroplating and electroless plating, Adding corrosion inhibitors. A great number of scientific studies have been devoted to the subjects of the first 3 techniques above (Song, 2005). But the last one, adding corrosion inhibitors has been seldom involved. Inhibitors are chemicals that react with a metallic surface, or the environment this surface is exposed to, giving the surface a certain level of protection (Roberge, 2000). For the metals widely employed in the industry such as iron, copper, zinc and aluminum, adding corrosion inhibitors is an effective and convenient method to decrease the corrosion rate. For magnesium and its alloys, there are very few publications on their corrosion inhibitors and only few inhibitors such as the salts of F(Song, 2005), Cr2O72(Song, 2006), 8hydroxyquinoline (Galio et al, 2010), and so on, are involved. Since Fand Cr2O72pollute the environment seriously, it is quite necessary to pay more attention to develop the environmental friendly corrosion inhibitors for magnesium and its alloys.