Friction is an important factor that causes frictional heat generated in the friction stir welding process and makes the joint between work pieces. The objective of the present work is investigate on the effects of friction stir welding parameters on the mechanical properties and material flow in AA1100 aluminum and A441AISI joint. In this study, tool offset, plunge depth, welding linear speed and tool rotational speed were chosen as variable parameters. Comprehensive analysis using the experimental results showed that the strongest joint obtained at 1.3 mm tool offset and 0.2 mm plunge depth when to the offset tool rotational speed and linear speed were 800rpm and 63mm/min respectively. Fracture locations in tensile test at all samples were in aluminum sides. Internal defects that caused in lower tool rotational speed removed by increasing the revolving and with growing trend in linear speed due to the more forging force, the surface defects abated. The maximum strength of welded joints with selected parameters was 90% aluminum base metal. In this research, microhardness of joint interface ascended with increasing rotational speed. This phenomenon is due to formation of thick intermetallic layers in abutting edges of sheets.