Magnesium-based alloys

In the nuclear engineering field special magnesium-base alloys are extensively used as canning materials for uranium in gas-cooled reactors. 

The unequal attack which occurs in tap water, condensate and other mild electrolytes may lead to perforations of thin-gauge sheet and even to deep pitting of castings. In stronger electrolytes the effect is variable. In chloride solutions such as sea-water, attack on the metal usually results in the pitting of some areas only, but where the metal surface has been rendered reactive, as by shot blasting, attack may be so rapid that uniform dissolution over the whole surface may occur. In either case magnesium-base alloys are not usually suitable for use in aqueous liquids since they are not intrinsically resistant to these electrolytes. 

Fig. 4.17 Samples of high-purity AZ31 (upper photographs) and ZW3 (lower photographs) magnesium-base alloys, fitted with mild-steel nuts and bolts and exposed to a variety of corrosion conditions, (a) 4-S hours immersion in 37 salt soln., (b) 180 days immersion in distilled water, (c) 4 days immersion in borehole water, (d) 180 days in humidity cabinet sea-water spray and (e) 180 days atmospheric exposure...

The proneness or otherwise to corrosion is essentially the same in all the magnesium-base alloys and it is important to note that the requirements of protection therefore do not vary for the magnesium alloy under consideration. If conditions are such that any one of the alloys can be used satisfactorily without protection, then any other of the alloys can be so used. On the other hand, if a given protective scheme is found necessary for a particular alloy, then the same protective scheme will be found necessary (and will be equally effective) with any other magnesium-base alloy. 

Table 4.20 The more usual cleaning and chromating processes for magnesium-base alloys ...

The objective is to achieve a balance between using materials that can have drugs within them, elute the drugs, and have a surface material that can potentially coat the stent and make it more biocompatible. Another approach is making the stent itself disappear. These might be made of a magnesium-based alloy that essentially disappears over about six months. 

The reduction proceeds via the addition of calcium to a magnesium based alloy which is covered with a fused salt... 

B. A. Shaw and R. C. Wolfe, Corrosion of magnesium and magnesium-base alloys, in ASM Handbook, Vol. 13B, Corrosion Materials, ASM International, Materials Park, OH, 2003, p. 205. 

An experimental magnesium-base alloy sheet containing 14 % lithium and 2 % aluminum was reported to have experienced intergranular layer attack similar to the exfoliation of 2duminum-copper alloys [8],... 

Logan, H. L. and Hessing, H., Stress Corrosion of Wrought Magnesium Base Alloys," Journal of Research of the National Bureau of Standards, Vol. 44, 1950, pp. 233-243. 

Microstructural properties such as grain size and phase distribution also play a role in determining corrosion behavior (Albright, 1988). Recent studies (Aune, 1983 Lunder et al., 1987) have found that fine, uniformly dispersed, cathodic phases were the most detrimental to the corrosion resistance of magnesium-based alloys (Albright, 1988). 

Mitsuo A, Aizawa T, (2003), Cold coating of magnesium base alloy films by ion beam sputtering , Materials Science Forum, 419-422, 927-930. 

Schippman D, Weisheit A, Mordike BL, (1999), Short pulse irradiation of magnesium based alloys to improve surface properties . Surface Engineering, 15, 23-26. 

RS Busk, Magnesium Products Design Marcel Dekker, New York, 1986, 256. DK Priest, FH Beck, MG Fontana, Stress corrosion mechanism in a magnesium-base alloy. Transactions of the American Society for Metals, 1955, 47, 473-492. 

More than 200 years after the first production of elemental magnesium (Mg) by Sir Humphrey Davy, the attention to magnesium-based alloys as biomaterials has increased during the past decade with biomaterial scientists and medical device developers (Mantovani and Witte, 2010). Surprisingly,... 

Barton, T F (1998), Anodization of magnesium and magnesium based alloys. US Patent 5792335. 

Kobayashi, W Takahata, S 9 S), Aqueous onodiTing solution and process for colouring article of magnesium or magnesium-base alloy. US Patent 4551211. 

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