Abstract
A feasibility investigation has been carried out of the formation of surface composite by uniformly distributing SiC particles 1.25 mu m in size into a surface layer of an A 1050-H24 Al plate through friction stir processing (FSP). The SiC particle was filled into a groove cut on the Al plate, covered by an Al sheet 2 mm thick, and a rotating tool was penetrated from the cover sheet so that the probe tip reached a depth beyond the groove bottom. The effects of process parameters (rotation speed and travelling speed) and applying multiple passes on the distribution of SiC particle in the nugget zone were investigated. The effects of groove size and its position relative to the tool probe were also investigated. Applying multiple passes had a great effect on the homogeneity of the SiC particle distribution. At rotation speeds of 2000-3000 rev min(-1), the SiC particles tended to cluster in some places in the nugget zone. By decreasing the rotation speed to 1000 1500 rev min(-1), the SiC particle was distributed in almost all the nugget zone area when the groove was 2-3 mm wide and 1.5 mm deep. On the other hand, the stirring action of FSP was insufficient to distribute homogenously the SiC particles when the groove size was increased to 362 mm. By shifting the groove position towards the advancing side of the tool probe, the distribution of the SiC particles in the nugget zone became better. The defect free nugget zone with homogenously distributed SiC particles was obtained in a sample produced by FSP at rotation speeds of 1500 rev min(-1) for the first pass and 1250 rev min(-1) for the second and third passes. Microhardness of the nugget zone was increased to a level as high as 55 HV when the groove size was 3 x 1.5 mm. The effect of the rotation speed on the particles dispersion was discussed with particular reference to the vertical material flow in the nugget zone.