Production of high strength metal matrix nano composite reinforced by CNT has been the base of many researches in the field of material engineering. In the present work A356-CNT cast nano composites were produced by stir casting and compocasting techniques. CNTs were injected into the melt in two different forms of raw CNT or Al-Ni-P-CNT composite powders. The composite powders were produced by Ni-P electroless plating technique. The effects of CNT addition and casting method on the microstructural, mechanical and electrical properties of the produced nano composites were investigated. Bath temperature of 80°C, bath pH of 5.5, CNT concentration of 1.25g/lit, Al particles to CNT ratio of 6 and stirring speed of 500 rpm were recognized as the optimum Ni-P electroless plating parameters for production of Al-Ni-P-CNT composite powders. The results revealed that addition of CNTs in the form of composite powders decreased the grain size of the matrix alloy. For the composites cast from the fully liquid state, the secondary dendrite arm spacing was decreased by about 60% and for the semi-solid cast samples the average equivalent circle diameter of ? Al particles was decreased by about 27%, when the CNTs were added by injection of Al-Ni-P-CNT composite powders into the melt. As a result, hardness, wear resistance and tensile properties of the composites were increased. Elastic modulus, yield strength and ultimate tensile strength of the composites produced by injection of composite powders was significantly improved compared with the matrix alloy or the composite produced by injection of untreated CNT. While the un-reinforced alloy kept less than 70% of its strength at 300?C, the semi-solid composites samples kept more than 90% of their strength at this temperature. The bending strength of the composite samples was increased by about 30% compared to that of the corresponding monolithic samples. Electrical conductivity of all composite samples was decreased by addition of CNT compared to that of monolithic samples
