6063-T5 aluminum alloy finned radiator products with a thickness of 17.6 mm were successfully fabricated by friction stir welding. Optical microscope and scanning electron microscope were used to analysis the microstructures and fracture of the joint, and the tensile properties were tested. The results show that the lamellar tearing defects in the surface of the weld is caused by the oxide aggregation distribution. The chemical composition of the oxide layer is mainly Al2 O3 and Mg O. In terms of mechanical properties,the tensile strength of the joint is 170 MPa after 180 ℃,10 h aging treatment,which is 106% of the base metal,the tensile fracture location occurred at the heat affected zone of advanced side with a ductile fracture mode.