Microstructure modeling of dynamic recrystallization in joining dissimilar Al to Cu sheets by high-speed friction stir butt welding

Abstract

High strength and mechanical properties were achieved in dissimilar joining of AA6061-T6 to Cu by high-speed friction stir butt welding (HSFSBW). Identifying the best parameters to achieve appropriate strength and hardness in experimental tests is a significant challenge. To solve this challenge, welding simulation was performed with various rotational and traverse speeds based on Lagrangian analysis. Microstructural evolution was examined using the Cellular Automata (CA) and Laasraoui Jonas (LJ) methods, considering thermomechanical conditions resulting from dynamic recrystallization (DRX). The best welding parameters were obtained with a rotational speed of 2000 rpm and a traverse speed of 120 mm/min with a ultimate grain refinement and tensile strength of 177 MPa, equivalent to 80% of the strength of the Cu base material. The results indicate that higher parameters compared to the best parameter lead to the creation of unsuitable surface morphology and defects in the weld. The rain size at 1500 rpm and 50 mm/min increased by 2.3-fold on the Aluminum side and 2.7-fold on the Cu side compared to the best parameter. Furthermore, initiation of grain refinement begins at 1800 rpm and 80 mm/min, with a 1.8-fold times difference in grain size compared to 1500 rpm and 50 mm/min. The results indicate that the grain size variation in the tests was reported to be between 1% to 12%, with the most significant impact of grain refinement observed in the stir zone (SZ). The grain size in this zone for dissimilar sheets varies between 9.5 and 11.5 micrometers.