A study of concave shoulder angle on the mechanical properties and fractography of friction stir welded AA6061-T651 joints

Abstract

AA6061-T651 material joints produced by friction stir welding (FSW) were analysed in this study. The analysis was conducted to determine the effect of the concave shoulder angle (CSA) of the tool on mechanical and fractographic properties. The mechanical properties studied included impact strength (IS) and hardness (HS), while the fractography included impact fracture and microstructure. The experiments used a Taguchi L16 (44) orthogonal array and were done thrice. The best parameters were then used four times for confirmation. The research findings confirmed that the change in CSA significantly impacts the IS of welded joints. Combining both artificial neural network (ANN) and genetic algorithm (GA), it was found that 9° is the best CSA for IS. The mechanical properties test results showed an IS of 0.806 J/mm2. The HS of the weld nugget zone (WNZ) decreased by 25.49 % compared to the parent material zone (PMZ). This decrease in HS is due to the phase change of magnesium silicide (Mg2Si), resulting in finer grains in the WNZ than in the PMZ. Meanwhile, the fracture angle of the impact test specimens was 81.7°, indicating moderate toughness characteristics.

Keywords

• Concave shoulder angle
• Friction stir welding
• Fractography
• Microstructure
• ANN-GA
• AA6061-T651