Alloy magnesium

These are available as (i) cast alloys and (ii) wrought alloys. The two major cast alloy systems are 2-10% A1 with minor amounts of Zn and Mn, and Mg alloyed with rare earths, zinc, thorium, and silver without aluminum. The alloys devoid of zirconium are satisfactory in performance in the temperature range 95-120°C. The alloys containing zirconium have better high-temperature properties. Heat-treatment of the cast alloys results in improved properties. 

Wrought materials are produced by extrusion, rolling and press forging in the temperature range of 300-500°C. Wrought alloys are of two types, namely those containing zirconium and those devoid of zirconium. The typical composition and mechanical properties are noted in Table 4.68. 

Several investigators have obtained evidence that magnesium dissolves anodically to a large extent as Mg+ and that this ion in solution reduces water to form Mg plus H2 (see Section 13.6). 

Magnesium has the lowest density (1.7g/cm ) of all structural metals, having about one-fourth the density of iron and one-third that of aluminum. This very low density makes magnesium and magnesium alloys useful wherever low weight is important, if not required. 

Because unalloyed magnesium is not used extensively for structural applications, it is the corrosion resistance of magnesium alloys that is of primary interest. To enhance strength and resistance to corrosion, magnesium is alloyed with aluminum, lithium, zinc, rhenium, thorium, and silver, with minor additions of cerium, manganese, and zirconium sometimes being used as well. 

Alloys containing 2-10% aluminum with minor additions of zinc and manganese these alloys are used up to 95-120 C (200-250°F), above 

Alloys containing various elements (rare earths, zinc, thorium, and silver), but not aluminum, and containing zirconium, which provides grain refinement and improved mechanical properties these alloys provide improved elevated temperature properties compared to those in the first group. 

The major alloying elements are manganese, aluminium, zinc, zirconium, silicon, thorium, and rare earth metals (E). At present E elements are the most promising candidates for magnesium alloys, with high temperature stability as well as improved corrosion behavior. E metals are forming stable intermetallic compounds at high temperature and therefore they decrease casta-bility. Aluminium and zinc are introduced mainly to 

Solute element Maximum solubility (wt%) i(at%) Adjacent intermetallic phase Melting point of intermetallic phase (°C) Type of equilibrium 

Wrought magnesium alloys are not used widely. The application of AZ31 is most common for forgings, extrusions, as well as for sheetmetal. There is an increasing demand for the use of wrought magnesium alloys, especially in the automotive industries, in the form of sheet 

Improve castability tendency to microporosity increase fluidity of the melt refine weak grain Improve castability reduce microporosity 

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Very small quantities of bismuthine are obtained when a bismuth-magnesium alloy, BijMgj, is dissolved in hydrochloric acid. As would be expected, it is extremely unstable, decomposing at room temperature to bismuth and hydrogen. Alkyl and aryl derivatives, for example trimethylbismuthine, Bi(CHj)3, are more stable. 

Small amounts of yttrium (0.1 to 0.2%) can be used to reduce the grain size in chromium, molybdenum, zirconium, and titanium, and to increase strength of aluminum and magnesium alloys. 

TABLE 11.60 Type N Thermocouples Nickel-14.2% Chromium-1.4% Silicon Alloy vs. Nickel-4.4% Silicon-0.1% Magnesium Alloy... 

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