EFFECT OF ULTRASONIC VIBRATIONS ON THE AGE HARDENING CHARACTERISTICS OF SOME ALUMINUM-BASED ALLOYS.

Two alloys conforming to ASTM 2024 and 7075 were tested. Ultrasonic irradiation accelerated the ageing rate. Under specific conditions of treatment, the ageing time could be reduced by as much as 50%. The peak hardness and strength achieved were higher than those achieved by conventional methods and without any noticeable fall in ductility. Scanning electron microscopy studies of fracture surfaces showed smaller and more numerous voids in specimens aged with ultrasonic pretreatment, probably indicating the formation of a larger number of nucleating centers. Transmission electron microscopy revealed a dislocation substructure in specimens subjected to ultrasonic irradiation prior to ageing. The increased strength is probably atrributable to pinning of dislocations by precipitate particles.