الفهرس 
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Abstract
In the present investigation, A390/Graphite and A390/Al2O3 as well as A390/Al2O3/Graphite surface composites were fabricated using Friction Stir Processing (FSP). The surface composite were fabricated using different tool rotational and traverse speeds. The effect of these speeds on the microstructural, mechanical and tribological characteristics of the developed surface composites was studied.The results revealed that the FSP is an effective technique for developing surface composites. However, the microstructural, mechanical and tribological characteristics of the developed composites depend significantly on the FSP parameters such as the tool rotational and welding speeds. The FSP significantly improved the structure of the as-cast A390 Al-Si alloy. The both coarse eutectic structure and coarse primary silicon particles was broken into a fine eutectic structure and small Si particulates. Moreover, the large voids near the surface were eliminated. The distribution of primary si particulates dispersed into the A390 matrix was found to be significantly dependant on the tool rotational and traverse speeds.The hardness of the surface composite layer depends on the FSP processing parameters, typically, the tool rotational and traverse speeds. At constant traverse speed, increasing the tool rotational speed increases hardness of the surface composites. The traverse speed has less significant influence on the hardness of the surface composites than the tool rotational speed. The A390/Al2O3 surface composites exhibited higher hardness when compared with the hardness of both A390/Graphite and A390/Al2O3/Graphite surface composites. It has been found that, for A390/Al2O3 and A390/Graphite surface composites, increasing the tool rotational speed within the studied range reduces the wear rate of such surface composites. In contrast, it has been found that, for A390/Al2O3/Graphite surface composites, increasing the tool rotational speed within the studied range increases the wear rate. The A390/Al2O3/Graphite surface composites exhibited the maximum wear resistance when compared with the both A390/Al2O3 and A390/Graphite surface composites.