Magnesium alloys, solubility

Chromates are very effective inhibitors of the corrosion of magnesium alloys by saline and other waters, and many treatments have been developed by means of which substantial hlms containing slightly soluble chromate are formed in the metal surface. Except on parts which are to be exposed only to a rural atmosphere, chromate treatment must be supplemented by paint, for which it provides a good base. 

SAFETY PROFILE A poison by ingestion, subcutaneous, parenteral, and intravenous routes. An irritant to skin and eyes. When heated to decomposition it emits vety toxic fumes of NO. An oxidizer. Mixtures with finely divided aluminum-magnesium alloys are easily ignitable and extremely sensitive to friction or impact. Such mixtures are used in chemical photoflash applications. Incompatible with (Mg + Ba02 + Zn), Al, and Mg alloys. When heated to decomposition it emits toxic fumes of NOx. See also BARIUM COMPOUNDS (soluble) and NITRATES. 

Uranium/Plutonium/Thorium Partition. After the reduction step, the metals partition according to their solubility in the magnesium alloy. Magnesium is used as the focus metal because it provides a means of separating uranium from plutonium. 

Modifications. It should be noted that both of the solvent elements, copper and silver, are monovalent, i.e. they both have atoms in which there is only one outer-layer or valency electron, while the solute elements, zinc, magnesium, cadmium and berylium, are all divalent, i.e. they all have atoms with two outer-layer or valency electrons. We shall soon be in a position to show how important in alloy structures these valency electrons can be we must content ourselves for the moment, however, by stating that Hume-Bothery has examined the solid solubility of various metals in the divalent solvent magnesium, and has shown that the favourable size-factor principle may be equally well applied to magnesium alloys, typical of... 

Table 3.1-2 Solubility data and intermetaUic phases in binary magnesium alloys [1.4]...

The mechanism which fixes the tolerance limit could be related to the solubility of the impurities in the magnesium alloy matrix. When the concentrations of Fe, Ni, and Cu exceed their tolerance limits, they could segregate and serve as active catalysts for electrochemical attack (Mercer and Hillis, 1992). However, in their study of tolerance limits, Hanawalt et al. (Hillis, 1983) failed to find any correspondence between the magnitude of the tolerance limit and the solubility of the added element in solid or liquid magnesium. They found only that corrosion began at discrete centers, and they supposed that the elements showing tolerance-limit phenomena were dispersed in the alloy as fine particles (Hanawalt et al.. 

Kol] Kolpachev, A.A., Medvedeva, N.D., Samoilov, Yu.A., Titova, LA., Effect of Iron on Titanium Solubility in Aluminium and Aluminium-Magnesium Alloys (in Russian), Tekh-nol. Legk Splavov, Nauchno-Tekh. Byull, Vses. Inst. Splavov, 8, 15-17 (1973) (Experimental, 3)... 

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