Aluminium-magnesium-silicon alloys

If Ihe main incoming male contacts are made ol aluminium alloy, which is normally a eompnsilioii of aluminium-magnesium and silicon, they must be provided wiili a coat of bron/e. copper and tin to give it an adequate mechanical hardness and resistance to corrosion. For more details refer to Section 27.2..5. 

Almond shell Aluminium, atomized Aluminium, flake Aluminium-cobalt alloy Aluminium-copper alloy Aluminium-iron alloy Aluminium-lithium alloy Aluminium—magnesium alloy Aluminium-nickel alloy Aluminium-silicon alloy Aluminium acetate... 

Individually indexed alloys or intermetallic compounds are Aluminium amalgam, 0051 Aluminium-copper-zinc alloy, 0050 Aluminium-lanthanum-nickel alloy, 0080 Aluminium-lithium alloy, 0052 Aluminium-magnesium alloy, 0053 Aluminium-nickel alloys, 0055 Aluminium-titanium alloys, 0056 Copper-zinc alloys, 4268 Ferromanganese, 4389 Ferrotitanium, 4391 Lanthanum-nickel alloy, 4678 Lead-tin alloys, 4883 Lead-zirconium alloys, 4884 Lithium-magnesium alloy, 4681 Lithium-tin alloys, 4682 Plutonium bismuthide, 0231 Potassium antimonide, 4673 Potassium-sodium alloy, 4646 Silicon-zirconium alloys, 4910... 

Magnesium and zinc are readily oxidized, and are liable to undergo oxidation during the storage of mixtures containing them, hence they have not been utilized for military purposes. Apart from this, magnesium is a valuable component of various pyrotechnic mixtures such as those used in signals or for illumination, for which it is hard to find a substitute. With the exception of calcium silicide the silicon alloys burn with more difficulty and are less efficient. For this reason aluminium and calcium silicides are the most widely used. 

The ignition point of metallic cerium is 160 C, which is quite low. However simple cerium is too soft to use and it is easily oxidized in the air. Therefore it is mixed with iron to form an alloy. This alloy of cerium and iron in v/eight ratio 65 35 is called Auer s metal. Nickel and cobalt-etc. can also be used instead of iron. Other kinds of alloys consisting of aluminium, magnesium and silicon are also used. 

Aluminium yields many valuable alloys. Magnalium consists of aluminium with 1 to 2 per cent of magnesium duralumin contains up to 5 per cent of copper with small amounts of Mg, Mn, Fe, and Si it has a low coefficient of expansion with rise of temperature, and plates of duralumin are only one-third the weight of equally strong steel ones. There is a growing interest in aluminium bronzes, alloys of aluminium and copper which are resistant to seawater and certain concentrations of sulphuric acid. Alloys of aluminium and silicon are also becoming important. 

Phosphorus is technologically and economically important in aluminium-silicon alloys. On one hand it regulates the mechanism of solidification of eutectic (12.5 % Si) and nearly eutectic alloys, on the other hand it grain refines the primary silicon in the hypereutectic system (15-25 % Si) When the eutectic or nearly eutectic aluminium-silicon alloys contain less than 5 Mg/g of phosphorus, the alloy solidifies into a lamellar structure. When the phosphorus concentration is above 9 Mg/g a globular structure is obtained. In hypoeutectic alloys with about 7 % of silicon, the solidification is only fine lamellarly at phosphorus contents between 2 ig/g and 4 g/g. When magnesium is present, even below 2 ng/g a globular structure is obtained. 

As has been shown by initial comparison tests with activation analysis techniques under the auspices of Eurisotop and BCR Study Groups, good results are obtained with aluminium-silicon alloys - free from magnesium or only containing less than 3000 pg/g of it - if reducing fusion in a stream of carrier gas is employed in the manner suggested by Kraft and Kahles (47) for the analysis of unalloyed aluminium, with the sole difference that the reaction temperature is increased to 1950°C. Like for unalloyed aluminium, the oxygen contents reported are near the detection limit, and only increase to values of a few pg/g at silicon contents of 7 % or more. 

Phi] Phillips, H.W.L., Varley, P.C., Constitution of Alloys of Aluminium with Magnesium, Silicon and Iron , J. Inst. Met., 69, 317-350 (1943) (Phase Diagram, Experimental,, , 11)... 

Alloys of aluminium with magnesium or magnesium and silicon are generally more resistant than other alloys to alkaline media. The corrosion rate in potassium and sodium hydroxide solutions decreases with increasing purity of the metal (Fig. 4.9), but with ammonium hydroxide the reverse occurs. 

Both silicon and aluminium are added to zinc to control the adverse effects of iron. The former forms a ferro-silicon dross (which may be removed during casting). Aluminium forms an intermetallic compound which is less active as a cathode than FeZn,] . Similarly in aluminium and magnesium alloys, manganese is added to control the iron . Thus in aluminium alloys for example, the cathodic activity of, FeAl, is avoided by transformation of FeAlj to (Fe, Mn)Al/. This material is believed to have a corrosion potential close to that of the matrix and is, therefore, unable to produce significant cathodic activity . 

We have seen that the adverse effect of impurities can, within limits, be controlled by alloying additions. Thus silicon and aluminium are added to zinc, and manganese to aluminium and magnesium, to counter the effect of iron. 

Intermediate alloy compositions include a zinc-15%-aluminium alloy for metal spraying (higher aluminium contents are unsuitable for spraying wire) and a zinc-30%-aluminium-0.2%-magnesium-0.2%-silicon coating (Lavegal) for sheet. 

Chlorine has caused numerous accidents with metals. Beryllium becomes incandescent if it is heated in the presence of chlorine. Sodium, aluminium, aluminium/titanium alloy, magnesium (especially if water traces are present) combust in contact with chlorine, if they are in the form of powder. There was an explosion reported with molten aluminium and liquid chlorine. The same is true for boron (when it is heated to 400°C), active carbon and silicon. With white phosphorus there is a detonation even at -34°C (liquid chlorine). 

Heat of combustion, thermal conductivity, surface area and other factors influencing pyrophoricity of aluminium, cobalt, iron, magnesium and nickel powders are discussed [4], The relationship between heat of formation of the metal oxide and particle size of metals in pyrophoric powders is discussed for several metals and alloys including copper [5], Further work on the relationship of surface area and ignition temperature for copper, manganese and silicon [6], and for iron and titanium [7] was reported. The latter also includes a simple calorimetric test to determine ignition temperature. 

Lead—tin alloys, 4877 Lead—zirconium alloys, 4878 Lithium—magnesium alloy, 4676 Lithium—tin alloys, 4677 Plutonium bismuthide, 0231 Potassium antimonide, 4668 Potassium—sodium alloy, 4641 Silicon—zirconium alloys, 4904 Silver—aluminium alloy, 0002 Silvered copper, 0003 Sodium germanide, 4412 Sodium—antimony alloy, 4791 Sodium—zinc alloy, 4792 Titanium—zirconium alloys, 4915... 

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