Characteristics of potential sources - vertical force, torque and current on penetration depth for quality assessment in friction stir welding of AA 6061 pipes

Friction stir welding of the pipes or curved bodies in aerospace components is tedious due to complex geometry, and hence, research articles related to it are rare. Primarily, this research has investigated the nature of vertical welding force, torque and current on the weld quality during the friction stir welding of Aluminium 6061 (AA 6061) pipe at different penetration depths – 1.4 mm, 1.54 mm, 1.66 mm, 1.7 mm, 1.9 mm and 2 mm. The feed rate and rotational speed have been set at 1 mm/s and 1800 rpm respectively. The weld quality has been evaluated using visual inspection and tensile test. From the results, penetration depths from 1.7 mm to 2 mm have been suitable for producing quality welds on a specimen with 2 mm thickness, which resulted in fewer shoulder marks, and percentage reduction of strength lower than 25.61% compared to the base metal. Friction stir welding using penetration depth of 1.4 mm has resulted in a weld, with excess shoulder marks and 43.84% of reduction in strength, which is not acceptable. In addition, the range of penetration depths (1.7 mm to 2 mm) for which the force remains constant is recommended for producing quality welds. While torque and power have increased linearly with the penetration depth, the distribution of the current has remained the same for different penetration depths. However, the current consumption has varied significantly in each one of the friction stir welding stages clearly distinguishing the tool penetration, the dwell time, the traverse tool movement and the tool pull out. The experimentation has been successful in laying the foundation for the process parameters signifying the importance of penetration depth.