THERMOMECHANICAL AGEING FOR 6XXX EXTRUSIONS

The present invention relates to extrusions for structural components, such as bumper, side impact beam, seat sill in vehicles and more particularly to a method for optimizing strength and energy absorption of 6XXX aluminium alloys extrusions by variations in thermomechanical ageing (TMA) consisting ini) an artificial preageing treatment with a duration t1 at a temperature T1 selected to increase the yield strength of said extrusion between 5% and 20%, said temperature T1 being typically between 120° C. and 180° C. and said duration t1 being typically between 1 and 100 hours, to obtain an artificially preaged extrusion,ii) a plastic deformation of said artificially preaged extrusion between 1% and 80% to obtain a deformed extrusion,iii) a final artificial ageing treatment of said deformed extrusion with a duration t2 at a temperature T2, said temperature T2 being typically between 140° C. and 200° C. and said the duration t2 being typically between 1 and 100 hours.