Magnesium alloys in ethylene glycol

E. Slavcheva, G. Petkova, P. Andreev, Inhibition of corrosion of AZ91 magnesium alloy in ethylene glycol solution in presence of chloride anions . Materials and Corrosion 56 (2005) 83-87. 

Alkali metals themselves also produce this reduction. The earliest system used was sodium in liquid ammonia 206,208,215), with which Kraus prepared trimethyltinsodium from hexamethylditin 206). Sodium-potassium alloy in ethylene glycol dimethyl ether also cleaves the same ditin J8). Most recently, lithium in tetrahydrofuran has been shown to cleave hexaphenyl-ditin 218,219) and hexa-n-butylditin 220). Also, hexaphenylditin may be cleaved by magnesium in tetrahydrofuran when the reaction is initiated by ethyl bromide 286). In an interesting variation, a catalytic amount of sodium in liquid ammonia causes the addition of vinylacetylene to hexaethylditin 287). 

Although the corrosion of pure magnesium in commercial coolants has been reported [9,31], in practice, an engine block cannot be made of pure magnesium, and the coolant cannot be pure ethylene glycol solution only. Therefore, it is important to understand the corrosion behaviour of magnesium alloys in commercial coolants. 

Magnesium alloys should have a similar corrosion behaviour to that of pure magnesium in an ethylene glycol solution. This has been eonfirmed by Fekry and Fatayerji s systematic study [30], which is briefly deseribed as follows. 

The inhibition effect of fluorides has also recently been observed on AZ91 in an ethylene glycol solution [30]. However, the effect is not as evident as on pure magnesium. This could be due to the content of alnminium in the alloy. Fluorides cannot inhibit the dissolution of aluminium. 

The likely mechanism of the inhibitive effect of KF on AM-SCl is similar to that for pure magnesium and AZ91D in a fluoride-containing ethylene glycol solution, i.e. fluorides react with magnesium in the matrix of AM-SCl alloy, forming a low-solubility magnesium fluoride product which deposits on the alloy surface and prevents further corrosion attack to the alloy. 

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