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Aviation History
1920
1920 - 0931.PDF
AUGUST 26, 1920 DURALUMIN BY E. UNGER AND E. SCHMIDT (Translated'from Teckmsche Benchte, VolTHE use of duralumin in the construction of aircraft makes an account of the properties of this material desirable,especially with reference to its working qualities as developed by experience. Composition, Specific Gravity and Melting PointDuralumin is made in various compositions, and has, with the exception of small quantities of impurities, thefollowing composition:— •• 95 ' 5 to 93 '2 per cent. 0-5 3-5 to 5-5 O'5 to o-8 ,, AluminiumMagnesium CopperManganese . Lead, tin and zinc, which, as is well-known, have an unfavourable influence upon the permanence of aluminum alloys, are not found in duralumin. , The specific gravity of duralumin varies according to com- position and hardness from 2.75 to 2.84. The melting point is about 6500 C. ! 7 e S ? 3~ 2Thickness of P/ate. -mm 75 70 65 GO S5 so to 12 16 20 24 28 3236^,, s Lenyfh of Ape/ny -hrs I n\ £ 4O0 420 44O -f€O 4W) SOO SZO Quench/nor 7e/n/3eraft"e.-°C 30 25 ZO 15 10 s 0 . Ill—Section 6, by STARR TRUSCOTT) Duralumin is made under this name by the Diirener Metallwerke, Duren (Rhld.), and under the name of Berg- metall by Carl Berg, Eveking (Westf.). Working of DuraluminLike other metals, duralumin can be rolled into plates and shapes and behaves in a similar manner, in that the elongationdecreases as the hardness of rolling increases. Tube blanks, however, can be made only by pressing, and not by theoblique rolling method. Fig. 1 shows the increase in tensile strength and decreasein elongation of a duralumin plate as its thickness is reduced by cold rolling from 7 mm. to 2 mm. The strength increasesfrom 41 kg. to about 54 kg. per sq. mm., while the elongation falls from 22.7 to 2.3 per cent. The curve shows that theelongation decreases very rapidly with the very first reduction in thickness. However, duralumin can be worked hot at a temperatureof about 4000 C. very well. TemperingDuralumin can be tempered, like steel, by heating and sudden cooling. For this purpose plates, tubes, and shapesare heated to between 480° and 510° and quenched, then aged ; that is, the treated material is simply set aside.The original strength characteristics are very nearly restored after the quenching, but the tensilestrength continues to grow with the time of ageing, from 35 to50 kgs. per sq. mm. The elongation does not decrease, but remains at mm 13 \ • 1 i .,i [\ \ \\ * •19 tet \ \ /re Bt / •\ varp t—— „ 7X. n / Ml 10 i'.I- $ s 0 O,S / i / / f\ v| \ / / > /I / / un 1 f -5 toe,/ r/v>r /T 7/0 en. SJ 7' mi j V ! ! *—. Thickness offi/erfes/nm o QS / 2 3Thickness ofjo/otes least the same, and usually increases slightly. In practicethe greatest strength is reached after about five days of ageing.When heated to over 5300 C. duralumin becomes unusable. Consequently the treating is carried on in a bath of nitrates,whose temperature can be carefully regulated and watched. During the ageing of the metal, work cannot be done on itwhich would change the section, as in that case the strength will not increase any more. After the completion of ageing,the material can be re-rolled in order to obtain smooth 933
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