Alloys containing magnesium

AI-Mg, Almost every commercial precipitation strengthened aluminum alloy contains magnesium as an alloying element. The Al—Mg system (Fig. 13) has a eutectic at 35% magnesium [7439-95-4] Mg, and 451°C. Maximum solid solubility is 14.9% Mg, and solubility decreases to about 0.8% Mg at room temperature. Despite this decreased solubihty, precipitation strengthening by the mestable p -phase precursor to the equilibrium p-phase Al Mg2... 

Fig. 14. Effects of iron (—), nickel (-), and copper (...) contaminant levels on the saltwater corrosion performance of magnesium AZ91 alloy containing...

Nickel-iron alloys are more resistant than iron to attack by solutions of various salts. In alternate immersion tests in 5% sodium chloride solution Fink and De Croly determined values of 2-8, 0-25 and 0-5 g m d for alloys containing 37, 80 and 100% nickel compared with 46 g m d for iron. Corrosion rates of about 0.4 g m d are reported by Hatfield for Fe-30Ni alloy exposed to solutions containing respectively 5 Vo magnesium sulphate, 10 Vo magnesium chloride and 10% sodium sulphate the same alloy corroded at a rate of about 1.2 g m d in 5% ammonium chloride. 

In tests lasting for 14 days, Copson found that the susceptibility of steel to stress-corrosion cracking in hot caustic soda solutions increased with increase in nickel content up to at least 8-5%. Alloys containing 28% and more of nickel did not fail in this period. In boiling 42% magnesium chloride the 9% nickel-iron alloy was the most susceptible of those tested to cracking (Table 3.38). Alloys containing 28 and 42% nickel did not fail within 7 days. 

There is a noticeable difference between the appearance of the aluminium-containing magnesium-rich alloys on the one hand and the zinc/zirconium-containing magnesium alloys on the other. In the former the microscopic pits in the surface which has been exposed to the weather tend to be narrow and relatively deep, while in the latter they are wider and tend to overlap, leading to a slightly wavy appearance. 

The special high-purity zinc (99-99%) is used mainly for the production of diecasting alloys containing 4% aluminium and 0 -04% magnesium and some-times I % copper, as shown in Table 4.30, which gives the composition of the two alloys laid down by BS 1004 1972, and of some newer zinc alloys. 

The fracture mode of stress-corrosion cracks in austenitic stainless steels can be transgranular, intergranular or a mixture of both. One of the earliest environments found to cause problems was solutions containing chlorides or other halides and the data due to Copson (Fig. 8.30) is very informative. The test solution for that data was magnesium chloride at 154°C the alloys contained 18-20alloy with a composition of approximately 18Cr-8Ni has the least resistance to cracking in this environment. 

Hydrogen absorption/desorption characteristics of magnesium-nickel alloy containing 23 atomic% Ni. (Reproduced with permission from Schwarz, R.B., Storage of hydrogen in powders with nanosized crystalline domains, Mater. Res. Bull., 24, 40, 1999, available at http //www.wtec.org/loyola/nano/US.Review/04 06.htm, May 2007.)... 

Acetylenic compounds with replaceable acetylenically bound hydrogen atoms must be kept out of contact with copper, silver, magnesium, mercury or alloys containing them, to avoid formation of explosive metal acetylides. 

The alloy used to make pop cans contains about 97% aluminum, by mass. The other elements in the alloy are magnesium, manganese, iron, silicon, and copper. 

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