Microstructure of weld interface between 6063 and S45C by means of friction stirring was observed by TEM. The reaction layer was formed along welding direction and depth direction of tool insert. The layers were composed of various intermetallic compounds such as Fe2Al5 and FeAl. The constitution differed with welding conditions. At 500 mm/min of welding speed, the interface had a thin reaction layer. At 1000 mm/min of welding speed, the interface had layered structure. However, both of the weld interfaces had a reaction layer under 1 μm and achieved high tensile strength of weld joint.
