Microstructural modification and enhanced mechanical properties of wire-arc additive manufactured 6061 aluminum alloy via interlayer friction stir processing

•6061 aluminum alloy was fabricated via hybrid WAAM and interlayer FSP technique.•WAAM + interlayer FSP specimen without porosity defects and grain boundary liquation.•The interlayer FSP can refine the grains and enhance the performances. In this study, an innovative hybrid additive manufacturing technology that combines wire arc additive manufacturing (WAAM) and interlayer friction stir processing (FSP) is designed to overcome the hot cracking and other solidification issues observed in WAAM of 6061 aluminum alloy. The grain boundary liquation and porosity defects are effectively eliminated by the interlayer FSP technique, and the coarse Si-rich phases are broken up and redistributed, and the coarse columnar grains are transformed into fine equiaxed grains, resulting in superior mechanical properties to the initial WAAM alloy. Furthermore, the anisotropy in strength of the WAAM sample can be eliminated by the WAAM + interlayer FSP technique. It demonstrates that the WAAM + interlayer FSP technique has great potential for use in the fabrication of aluminum alloys susceptible to hot cracking with high performance.