Microstructural and mechanical analysis of 6063-T6 aluminum alloy joints bonded by friction stir welding

For improving the comprehensive mechanical properties of aluminum alloys (AAs) joint, the 6063-T6 AAs with thickness of 10 mm were bonded via the double-sided (DS) friction stir welding technique. Compared with the single-sided (SS) AAs joint, the grains in various regions of DS joints were refined in various degrees. In addition, the high-angle grain boundaries frequency of nugget zone reached to approximately 55%, which could hinder crack growth. Fatigue test result indicated that fracture positions of DS joints were either at thermo-mechanically affected zone or heat-affected zone near advancing side, resulting in the fatigue strength of 92 MPa. However, the fatigue strength of SS joints those mainly fractured on welding root was 76 MPa. The approximately 20% higher fatigue strength of DS joint than that of SS joint was mainly attributed to the elimination of the weak bonding at welding root as well as the grain refinement.