Significance of plate position on the coupled thermal and material flow behavior in friction stir welding of dissimilar aluminum alloys

Abstract

The optimal plate position of dissimilar AA6061 and AA2024 alloys during friction stir welding (FSW) is one of the most critical parameters, which affects the mechanical properties of the joints. Although extensive experimental research has been conducted on this issue, the underlying mechanism remains unclear so far. In the present study, numerical simulation is employed to predict temperature distribution and material flow between different plate positions by proposing a 3D model based on computational fluid dynamics (CFD) method. Numerical results, including heat generation, temperature, horizontal and transverse material flow during welding between different plate positions, are quantitatively analyzed, and validated with corresponding experimental observations. It is revealed that both total heat generation and peak temperature with 6A/2R condition are lower than those with 2A/6R condition. However, material evolution in both horizontal and transverse sections indicates more effective material mixing and stronger mechanical locking of the joint with 6A/2R condition than that with 2A/6R condition. Consequently, tunnel defects are more prone to appear at joint bottom with 2A/6R condition, thus higher joint tensile strength is achieved with 6A/2R condition. By integrating numerical results with experimental observations, the superiority of 6A/2R over 2A/6R plate position during dissimilar FSW is demonstrated.