The effect of welding speeds and tool pin profiles on microstructure and mechanical properties of semi-solid metal 356 joints produced by friction stir welding was investigated. In this work, the joints were made by using a fixed rotating speed of 1750 rpm with varying welding speed of 80, 120 and 160 mm/min. In addition, two different types of tool pins, cylindrical and square pin, were applied. The Scanning Electron Microscope (SEM) reveals fine microstructure and uniform dispersion of Si (Silicon) particles obtained from cylindrical pin than that of square pin. Transverse and longitudinal tensile strengths obtained from cylindrical pin are greater than square pin. Furthermore, the joint made from 1750 rpm, 160 mm/min with cylindrical pin shows highest strength.