In this research casted Aluminum alloy A356 and Al2O3 powder were used as matrix and reinforcement, respectively. 5wt. % of Al2O3 with Al powder in the ratio of Al/Al2O3=1 for increasing the wettability were milled and injected to melt. Three different argon flow gas rate (2.5, 5, 10 liter/min) were selected for injection Al2O3(p) within molten Al and investigated the effects of that on microstructure and mechanical properties. Results showed, with increasing powder gas flow rate from 2.5 to 5 liter/min, mechanical properties such as hardness and compression strength are enhanced from 62.28 HB and 230.2 MPa to 78.7 HB and 539.1 MPa, respectively. While wear test represents decreasing of around 26 percent in coefficient of friction. But, with further enhancement in gas flow rate to 10 liter/min due to porosity increasing and agglomeration of Al2O3 particles, hardness and compression strength in comparison of composite with 5 liter/min flow rate reduced 21 and 37 percent, respectively. In this way, coefficient of moderate friction increased from 0.42 in composite with 5 liter/min flow rate to 0.56 in metal matrix composite with 10 liter/min flow rate.