An aluminum alloy and a process for treating the aluminum alloy. The alloy contains 0.5 to 2.5% by weight of an alloying mixture of magnesium and silicon, in which the molar ratio of Mg/Si is 0.70 to 1.25, the alloy optionally containing an additional amount of silicon up to about 1/3 of any iron, manganese and chromium in the alloy, as expressed by weight percent, the balance of the alloy being aluminum, optional alloying elements and unavoidable impurities. The process entails an ageing technique that includes a first stage in which an extrusion of the aluminum alloy is heated at a rate above 100.degree. C./hour to 100-170.degree. C., a second stage in which the extrusion is heated at a rate of 5 to 50.degree. C./hour to a final hold temperature, wherein the total ageing operation is performed in 3 to 24 hours.