The Effect of Ageing Time on Microstructure and Mechanical Properties of Aluminium Alloy A356

Reduced weight of automobiles for the purpose of fuel economy has encouraged the use of Al alloys in wheels. Alloy A356 (LM25) containing 7% Si & 0.3%Mg is widely used for its favourable properties such as excellent castability, good corrosion resistance, good pressure tightness etc. It is medium strength heat treatable hypoeutectic alloy. During solidification excess Si-Al eutectic appears as second phase. In case of A356, precipitates of Mg2Si are formed which are responsible for hardening. The precipitation sequence observed in A356 is alpha(SS)-> GP Zone ->beta"->beta'->beta (Mg2Si) In present work, A356 alloy is solution treated (550 degrees C) for 5 hours, quenched in water so as to get super saturated solid solution (SSSS) then subjected to ageing at various time intervals of 4,8,12,16,20 hours at fixed temperature (170 degrees C). The purpose is to determine optimum ageing time using different characterizing methods like hardness, microstructural observation & electrical conductivity.