STEEL SUBSTITUTES.

Press, Volume LXIII, Issue 19150, 5 November 1927, Page 9

STEEL SUBSTITUTES.

ALUMINIUM ALLOYS. Exhaustive research with aluminium alloys has occupied the investigation departments of motor manufacturing linns for many years, and some remarkably strong metals have been produced. Until about forty years ago aluminium was produced in only negligible quantities and was exhibited as a curiosity—in very small pieces, it should be mentioned, as it was priced at about L'l per ounce. The introduction of the electrolytic method of production resulted in a rapid increase in output and an enormous reduction in cost, and made possible the commercial utilisation of the metal. It was not, however, until an urgent demand was made for lighter metals for airship and aeroplane construction that serious attention was given to the production of aluminium alloys suitable for industrial requirements. There wore, of eouise, many of these light metals in use before the war. and although the early examples had no great tensile strength they were fairly easily cast; they were employed for Mich details of car construction as crankreases, gearboxes, radiator tops and othrr parts where lightness and ease of manufacture wore of more importance than groat strength. The metals used to alloy with aluminium were chiefly copper and zinc, either alone or together, and in, various proportions.

While these alloys proved to be suitable for the particular purposes to which they were put', they had not sufficient strength to replace steel for constructional work. The maximum strength, or breaking stress, of the alloys used for castings such as gearboxes was only about nine tons per square inch, compared with 25 to 30 tons for mild steel. . Thus, to obtain , the same strength in a part made from this alloy instead of from steel, the cross-section in the former case would have to lie nearly three times that in the latter. This would, therefore, negative the advantage of 1 using the lighter metal on theso grounds alone. A big step forward in tho development of these light alloys was made when duralumin was introduced. This is the trade name given to an alloy which, in one form, has the following composition : copper, 3 per cent.; manganese. 1 per cent.; magnesium, 0.5 per cent.: aluminium, 05.5 per cent. This metal has excellent mechanical properties and is amenable to heat treatment. In the soft annealed condition it can be forged and "worked" into any desired shape, and then, by quenching* in water or oil from a temperature of approximately oOOdeg. centigrade, and "ageing'"for several days, an internal structure is developed which results in a tensile strength of nearly 28 tons per square inch. The frames of Zeppelins were constructed of this light alloy, which, since the war, has been used successfully for industrial purposes in many directions. In Germany a motorcycle lias recently been marketed with a duralumin frame, fork and tank.