Infiltration behavior of Al-Mg alloys in SiC_p powder bed using pressureless infiltration technique have been studied. The manufacturing of Al/SiC_p composites by pressureless infiltration was successful when Mg was added over 8% in Al alloy matrix. Processing time and temperature to complete Infiltration through SiC_p bed was decreased with increasing Mg content in Al alloy. When Mg powder was added in SiC_p bed, processing temperature for successful infiltration was decreased. Volume fraction of SiC_p in composites was increased with increasing the mixing ratio of coarse SiC particles.