Aluminium-silicon alloys are widely used for automotive and aerospace applications due to their high strength to weight ratio. a356 (al-7si-0.3mg) this alloy is commonly used for automotive application because this alloy can achieve the optimum strength and ductility. cylinder head is one of the most critical component which is supposed to be brain of the engine. the higher strength and life of the cylinder head can improve the efficiency of the engine. jaya hind industries pvt. ltd. is one of the pioneer organization in manufacturing of cylinder head. this project work was carried out under the development of a356 cylinder head. so in this thesis we have studied about the effect of precipitation hardening heat treatment of t6 temper on microstructural behaviour and mechanical properties of a356 alloy. basically t6 heat treatment consist of solutionization at 540 °c for 5 hrs followed by water quenching at 70 °c for 30 minutes followed by artificial ageing at higher temperature of 200 °c for 5 hrs. in this thesis we have also studied about the effect of various ageing time and temperature combinations on microstructural behaviour and mechanical properties of a356 alloy to find out the optimum ageing parameter. after comparing the effect of various ageing parameter 230 °c/3hrs has been found out as an optimum parameter which can replace the present ageing parameter i.e. 200 °c /5 hrs. this optimum ageing parameter not only saves the energy but also increases the productivity.