Improvement of microstructure and fatigue performance of wire-arc additive manufactured 4043 aluminum alloy assisted by interlayer friction stir processing

Abstract

• This is the first time to report the application of interlayer FSP to assist the WAAM Al-Si alloy, and effectively eliminate the porosity and coarse dendrite in the WAAM as-deposited material. • The WAAM + interlayer FSP hybrid additive manufacturing significantly improves the ductility and fatigue performance of WAAM components. • The mechanism of the improved fatigue performance correlated with microstructure developed during WAAM + interlayer FSP process is discussed and clarified. To expand the application of wire-arc additive manufacturing (WAAM) in aluminum alloy forming components, it is vitally important to reduce the porosity, refine microstructure, and thereby improve the mechanical properties of the components. In this study, the interlayer friction stir processing (FSP) technique was employed to assist the WAAM of 4043 Al–Si alloy, and the related effects on the microstructure evolutions and mechanical properties of the fabricated builds were systematacially investigated. As compared to the conventional WAAM processing of Al–Si alloy, it was found that the introduction of interlayer FSP can effectively eliminate the pores, and both the α-Al dendrites and Si-rich eutectic network were severely broken up, leading to a remarkable enhancement in ductility and fatigue performance. The average yield strength (YS) and ultimate tensile strength (UTS) of the Al-based components produced by the combination of WAAM and interlayer FSP methods were 88 and 148 MPa, respectively. Meanwhile, the elongation (EL) of 37.5% and 28.8% can be achieved in the horizontal and vertical directions, respectively. Such anisotropy of EL was attributed to the inhomogeneous microstructure in the stir zone (SZ). Notably, the stress concentration can be effectively reduced by the elimination of porosity and Si-rich eutectic network fragmentation by the interlayer FSP, and thus the fatigue behaviour was improved with the fatigue strength and elongation increased by ∼28% and ∼108.7%, respectively. It is anticipated that this study will provide a powerful strategy and theoretical guidance for the WAAM fabrication of Al-based alloy components with high ductility and fatigue performance.