In the current investigation, friction stir processing (FSP) of aluminium alloy 6061 alloy was carried out under different cooling conditions to determine its influence on the microstructure evolution and properties of the investigated alloy. It was found that the type and distribution of the strengthening precipitates in the friction stir processed Al 6061 alloy significantly depend on the FSP parameters and working temperatures during FSP. The properties of friction stir processed alloy were evaluated using micro-hardness and bulk hardness tests. It was observed that 6061 alloy friction stir processed under rapid cooling conditions exhibited enhanced hardness which was found to vary between nearly 12 to 33% as compared to the alloy processed under ambient cooling conditions. © (2013) Trans Tech Publications, Switzerland.