Aluminum alloys are used in various industries but they suffer from several limitations such as low hardness and strength. To overcome these problems several approaches have been suggested including producing a composite of aluminum by adding a hard phase. Further, refinement of the grain size can significantly improve the properties of aluminum. In this research in situ aluminum-titanium nanocomposite was fabricated by a combination of accumulative roll bonding (ARB) and friction stir processing (FSP). ARB continued to 3 cycles and FSP performed for 5 passes with 16 mm.min -1 line speed and 1600 rpm rotation speed. Structure and properties of nanocomposite was investigated by optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD), thermal analysis (DSC, DTA) and hardness test. It was found that with increasing in number of ARB cycles Ti layers were broken to smaller particles. Annealing after ARB causes formation of primary Ti-Al intermetallic particles. FSP of these samples formed a nanostructure consisting of Ti and Ti-Al intermetallic compounds in Al matrix. Ti-Al intermetallic compounds formed in this step because of exothermic reaction between Ti and Al and also heat released during the FSP process. XRD results showed that the type of titanium aluminides that produced during FSP was TiAl 3 . XRD patterns also showed some not-reacted initial Ti particles in the composites. The hardness of ARB sample reduced to 28 BHN remarkably after annealing at 600°C for 180 minutes. Structure of nanocomposite refined and its hardness increased after FSP process. Maximum hardness was 81.4 BHN which was obtained after 3 passes of FSP. Keywords: metal matrix composite, accumulative roll bonding, friction stir processing, aluminum, titanium.
