Abstract: The material flow and micro-structural evolution in the friction stir welding of L2-Al to itself, L2-Al to T2-Cu, T2-Cu to itself and LF6-Al alloy to LDI0-Al alloy were studied under different welding conditions. The experinentel results show that the repeated dynamic recrystal is the reason for metal keeping flowing. Two main factors affecting metal plases flowing are deformation speed and welding temperature. The stir tool makes the material with high strain, and heat it quickly, which lead to aluminum recrystal, and flowing steady. A properly elevated welding temperature is good for metal softening, and can promote flowing,then achieve welding.