Magnesium binary alloys

FIG. 1—Corrosion rates of magnesium binary alloys determined in alternate immersion testing in 3 % sodium chloride [7]. 

New combined (or binary) alloy sacrificial anodes have been developed . An aluminium anode, for example, might have attached to it a short-life supplementary magnesium anode, or anodes, for quick polarisation of the structure. The overall reduction in structure current requirements is claimed to result in an anode weight saving of 35-50% . 

Magnesium Committee, 1987, Magnesium Manual 87 (Japan Light Metal Association, Tokyo) p. 58. Massalski, T.B., 1986, Binary Alloy Phase Diagrams (American Society for Metals, Ohio). 

The standard method to quantify element release is titration. There are standard procedures for most commonly used elements. Therefore titration can be recommended for pure magnesium or binary alloys with alloying elements for which established titration methods are available. The advantage is the relative low cost of the instrumentation (beaker and burette). The disadvantages are the use of special chemicals and the time-consuming procedure. For the titration of Mg ions calcium ions must be excluded. If calcium ions are present a further titration step has to be included. 

Figure 4.17. The binary phase diagrams of the magnesium alloy systems with the divalent metals ytterbium and calcium (Ca is a typical alkaline earth metal and Yb one of the divalent lanthanides). Notice, for this pair of metals, the close similarity of their alloy systems with Mg. The compounds YbMg2 and CaMg2 are isostructural, hexagonal hP12-MgZn2 type.

Charcoal and sulfur were the earliest pyrotechnic fuels. The choice of fuels is very wide, ranging from metallic to non-metallic elements and binary compounds to various types of carbonaceous materials, both natural and synthetic. The main fuels are aluminum and magnesium powders, their alloy, sulfur, lactose, carbon and carbonaceous fuels etc. The fuels listed below are usually powdered materials, which when oxidized provide heat energy. 

Other common anode materials for thermal batteries are lithium alloys, such as Li/Al and Li/B, lithium metal in a porous nickel or iron matrix, magnesium and calcium. Alternative cathode constituents include CaCr04 and the oxides of copper, iron or vanadium. Other electrolytes used are binary KBr-LiBr mixtures, ternary LiF-LiCl-LiBr mixtures and, more generally, all lithium halide systems, which are used particularly to prevent electrolyte composition changes and freezing out at high rates when lithium-based anodes are employed. 

Unlike most metals, the strength of aluminum improves upon alloying, which extends its range of applications (Table 3.5). One of the most popular alloys is the binary Mg/Al type, which is sometimes referred to as magnelium. Only a maximum of 5 wt% of Mg may be dissolved in A1 to provide solid-state strengthening. However, only 1.5 wt% of magnesium may be dissolved at room temperature, implying that... 

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

Hanawalt et al. (1942) studied the influence of 14 elements in binary magnesium alloys on the rate of corrosion in salt water. The results are summarized in Fig. 4-15. They found that four (Fe, Ni, Cu, and Co) had a very profound accelerating influence on the rate of corrosion in salt water at concentrations of less than 0.2% three (Ag, Ca, Zn) had a more modest influence at concentrations of 0.5 to 5%, and the remainder (Al, Sn, Cd, Mn, Si, and Na) had little, if any, influence at concentrations up to 5%. 

The presence of zinc in binary or ternary alloys has a decisive effect on film characteristics. Zinc can increase the tolerance limits and reduce the effect of impurities when the tolerance limit has been exceeded (Hillis, 1983). Addition of 1% Zn to pure magnesium increases the tolerance limit for nickel, but to lesser extent than addition of 1% Mn (Loose, 1946). Zinc is believed to improve the tolerance of Mg-Al alloys for all three contaminants (Fe, Cu, Ni), but its amount is limited to 1-3% (Froats et al.,... 

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