Explain age Hardening process used to strengthen an aluminium alloy diving cylinder Solution Precipitation hardening, or age hardening, provides one of the most widely used mechanisms for the strengthening of metal alloys. The fundamental understanding and basis for this technique was established in early work at the U. S. Bureau of Standards on Duralumin. The strength and hardness of some metal alloys may be enhanced by the formation of extremely small uniformly dispersed second-phase particles within the original phase matrix in a process known as precipitation or age hardening. The precipitate particles act as obstacles to dislocation movement and thereby strengthen the heat-treated alloys. Many aluminum based alloys, copper- tin, certain steels, nickel based super-alloys and titanium alloys can be strengthened by age hardening processes. The precipitation-hardening process involves three basic steps: 1).