This paper focuses on a rheo-forming of arm parts fabricated by an electromagnetic stirring system (EMS). This forming process takes place under high pressure of high pressure die casting and thin-walled casting is possible. Also, the productivity is higher than for low pressure die casting because of the shorter cycle time. Rheo-forming is advantageous because forming is performed in the semi-solid state with laminar flow and the gas content is low, which makes welding possible. Therefore, this paper examines arm parts with EMS and has investigated the mechanical properties after T6 and T5 heat-treatment.