Age Hardening of Aluminium

Aluminium alloy development began when the properties of the unalloyed metal were insufficient to meet the needs of potential customers. In 1906 a German metallurgist, Alfred Wilm, was investigating the effects of adding copper and other metals to aluminium in the hope of finding a stronger replacement for brass in cartridge cases. One such alloy, AI-3.5%Cu-0.5%Mg, was heated and quenched into water to see if it would harden like steel given a similar treatment. Initial results were disappointing but, to his surprise, tests made by chance some days later revealed that the alloy had become significantly harder and stronger. The phenomenon was called "age hardening" and it represented the only new method of hardening alloys by heat treatment since the effects of quenching of steel were discovered in the second millennium BC In 1909, Wilm gave to the Durener Metallwerke in Duren sole rights to his patents and this firm produced the first sheet in the famous composition known as "Duralumin". This alloy was quickly adopted in 1911 for structural members of the Zeppelin airships and then for the first all metal aircraft, the Junkers F 13, that first flew in 1919. Age hardened aluminium alloys have continued to be the principal materials for aircraft construction which, in turn, has provided continuing stimulus for new alloy development.