The role of thermal contribution in the design of AA2024 friction stir welded butt and lap joints: mechanical properties and energy demand

Although in recent times the use of solid-state welding processes as friction stir welding (FSW) has become increasingly widespread, for some joint morphologies, as lap joints, there are still significantly less data available on both process parameters optimization and energy consumption. In the present paper, the authors investigated the possibility of enhancing the joint quality in two different configurations, i.e. lap and butt joints, taking into account specific thermal contribution (STC) conferred to the weld. Strength, micro-hardness and microstructure were evaluated on the produced AA2024 aluminum alloys butt and lap joints. The surface response method (RSM) was used to investigate the effects of the main process parameters and to identify optimal technological parameters in terms of joint resistance, while the specific energy consumption (SEC) of the entire process was acquired with the aim to provide design guidelines taking into account, at the same time, mechanical performance and environmental impact. It was found that the same optimal range of revolutionary pitch can be identified for both the configurations. Additionally, maximizing welding speed, for a given revolutionary pitch, contributes to significantly reduce the environmental impact of the process with no detrimental effect on the joint performance.