In this research, a new application of friction stir processing (FSP) in producing surface composite on circular billets was introduced. Al/Cu composite was fabricated by FSP on the surface of a 1050 aluminium cylinder with the diameter of 60 mm. Then this cylinder with surface composite was extruded with the extrusion ratio of 1.7. Finally, microstructure and microhardness were investigated before and after the extrusion. H13 hot work steel was used as the material of the tool whose pin diameter and length were 6 mm and shoulder diameter was 18 mm. The rotation and traverse speed of the tool were 1000 rpm and 25 mm/min respectively. The microstructural investigations show that the thickness of the composite layer decreases and a uniform layer of the composite remains on the surface after the extrusion. Also the microhardness measurements demonstrated that the hardness of the composite layer was higher than the base metal and the microhardness of all zones increased after the extrusion.

Friction stir processing (FSP) was used to fabricate Al/Cu metal matrix composite (MMC). The effects of two different tool pin profiles (straight cylindrical and square) and the number of FSP passes on microstructure, tensile properties and microhardness were studied. The results indicated that good dispersion of micro-sized Cu particles, finer grains, higher tensile properties and higher microhardness, can be achieved by the square tool pin profile compared to the samples produced by the other tool. Also it was observed that the ultimate tensile strength of the samples produced by two FSP passes, as a result of Cu particles shattering, increased intensively compared to the samples fabricated with first FSP pass. Further FSP passes increased the elongation of the composites without any considerable changes in yield and ultimate tensile strength.