Friction stir welding (FSW) has got much attention as solid-state joining technique and provides an improved way of producing weld joints with ease of production. Aluminum based alloys usually exhibit low weldability on conventional fusion welding techniques. FSW is most suitable for aluminium based materials. This book focused on establishing the influence of inexpensive nano fly ash reinforcement material on the FSW weld joints of aluminium matrix based nano composites. The micro-structural aspects and morphological studies of the joints were discussed. Mechanical behaviour and wear aspects on the FSW joints were also elaborated. The optimisation process of material and FSW parameters were discussed elaborately.