Значение термина alloys, aluminium в knolik
alloys, aluminium - Alloys, Aluminium
alloys, aluminium - Some years ago Dr. Ludwig Mach experimented with alloys for the production of metal mirrors. It was considered indispensable that the composition aimed at should be light, hard, tough, and susceptible of polish, and that its gloss should not be easily affected by the air. An equal mixture of magnesium and aluminium proved a very suitable alloy. Following up this discovery, Dr. Mach systematically tried all possible proportions of magnesium and aluminium according to their properties and technical adaptability, giving the most approved one the name of magnalium, on the production of which he obtained patent rights. Before this, various experiments had been made, with a view to the discovery of suitable alloys; but as at that time neither of the two metals could be obtained technically pure, the alloys did not possess the valuable properties which distinguish the new magnalium.
Aluminium, as well as magnesium, is most difficult to work, inasmuch as the former chokes up the file, and is liable to break, while the latter is so tough that neither a file nor the turner's chisel can make any impression. Magnalium, on the other hand, is more suitable than either of its component parts. Alloys containing up to 30 per cent, of magnesium furnish a metal the hardness of which lies about half-way between yellow and red brass, and which may be easily worked with any tool; even the weakest screw-threads can be cut with proper keenness. The chips are like those of yellow brass, the faces of the pieces are smooth and bright, and choking never takes place even with the finest files. Magnalium, moreover, is chemically less assailable than either of its components. Aluminium by itself has a very indifferent exterior, while magnesium by itself is greatly affected by the air, and oxidation will gradually extend far into the interior. Magnalium is silvery white, remains unaffected by exposure to the air, nor can ammonia or acetic or sulphuric acid harm it in any way. It surpasses aluminium in gloss, tractability, firmness, and lightness.
The combinations of aluminium with copper or with zinc can easily be made, but as these two metals are a great deal heavier than aluminium, all the advantages due to the light weight of the latter are lost. While aluminium has a specific weight of 2.7, the alloys referred to range between 3 and 3.5. A notable contrast to this is presented by the specific weight of magnalium, which is less than that of pure aluminium - namely, 2 to 2.5 - according to composition. Magnalium produced in Sweden shows a specific gravity of only 2.4 to 2.7
Magnalium is sold in the form of bars, tubes, sheets, and wire. For melting purposes, crucibles of graphite or of iron are used, the inside of the latter having been lined with clay and magnesia. Molten magnalium can be poured into the thinnest vessels of a diameter of down to two millimetres and of the most intricate forms, and will fill them up thoroughly and faultlessly. It becomes soft at 570°, melts at 600°, and becomes fluid at 630° C. On account of its lightness and its silvery white colour it is in a high degree suitable for metallic mountings on photographic apparatus, optical instruments, and similar articles.
Unfortunately, sea-water is inimical to magnalium, especially when the latter comes in contact with other metals.
In cases in which, for technical purposes, great solidity is of paramount importance, as, for instance, in regard to large castings, an alloy of from 3 to 5 per cent, of magnesium is most suitable. An addition of 10 per cent, of magnesium would render magnalium brittle, while 30 per cent. of magnesium would reduce the solidity of the alloy still more. With only 2.4 per cent, of magnesium added, magnalium can be forged at a temperature of 400° C., and will then act in a similar way to copper at red heat. If containing less than 5 per cent, of magnesium, it may be forged in the cold state, and if perchance the hammering has rendered it too hard, it can be made malleable again by heating to a temperature of 500° C., and chilling it thereupon in cold water. ('Journal' of the Franklin Institute.)
(b) A writer in the 'Aluminium World' gives the constituents of a hard alloy which has been found very useful for the spacing levers of typewriters. The metal now generally used for this purpose by the various typewriter companies is "aluminium silver" or "silver metal," The proportions are given as follows:
This alloy when used on typewriting machines is nickel-plated, for the sake of the first appearance; but so far as corrosion is concerned, nickeling is unnecessary. In regard to its other qualities, they are of a character that recommends the alloy for many purposes. It is stiff and strong and cannot be bent to any extent without breaking, especially if the percentage of aluminum is increased to 3.5 per cent.; it casts free from pinholes and blow-holes. The liquid metal completely fills the mould, giving sharp, clean castings, true to pattern; its cost is not greater than brass; its colour is silver white, and its hardness makes it susceptible of a high polish.
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