DURALUMIN

Evening Post, Volume CIV, Issue 68, 17 September 1927, Page 24

DURALUMIN

Until about forty years ago alumiuium was produced in only nogligiblo quantities, and was exhibited as a curiosity—in very small pieces, it should bo montioned, as it was priced at about t" por ouncol Tho introduction of tho electrolytic method of production rosultcd in a rapid increase in output and an enormous reduction in cost, and made possiblo tho commercial utilisation of tho metal. It was not, however until an urgont demand was mado lor lighter metals for airship and aeropiano construction that serious attention was given to tho production of aluminium alloys suitable for industrial requirements. There wore, of course many of those light metals in uso beforo the war, and although tho early oxamplcs had no great fcensilo strength they woro fairly easily cast; they woro employed for such details of car construction as crankcases, gearboxes, radiator tops, and other parts whoro lightness and oase of manufacture wero of moro importance than great strength. Tho metals used to alloy with aluminium woro chiefly, coppor and zinc, either alono or togothcr, and in various proportions.

While thoso alloys proved to bo suitable for tho particular purposes to which they wore put, they had uot Kufiiciont strength to replace steel for constructional work. The maximum teusilo strength, or breaking stress, of tho alloys used for castings such as gearboxos was only about nine tons per squaro inch, compared with 25 to 30 tons for mild stool. Thus, to obtain tho samo strongth in a part made from this alloy instead of from stool, tho cross-section in tho formor cuso would havo to bo nearly throo timos that in tho latter. This would, therefore, negative tho advantage of using the lighter metal on theso grounds alone A big stop, forward in tho development of theso light alloys was made when duralumin whs introduced. This is tho trado name givon to nn alloy which in ono form, has tho following composition:—Copper, 3 por cent.; manganese, J. per cent; magnesium, 0.5 por cont • aluminium, 05.5 per cent. This metal has excollenf, mechanical properties and is amcnablo to hoat treatment. In tho soft .annealed condition it can be forced and worked" into aiiy dosired shapo. and then, by quenching in water or oil from a temperature of approximately 000 dogreea Oontigrado, and "aging" for several days, an internal structure is developed which results ia a tonsile in rr S%? f searly5 early 28 ttms P« "I"*™ inch. The frames of Zeppelins were ""truetea of thia light alloy, wWch, since the war, has beon used auceess' fully for industrial purposes in many dxrectxons. In Germany a motor-cycle has rpcontly boon markoted with a wldc^T- tTr°> forkB ' t™C*t e , tno world for its power.