Microstructure evolution and grain refinement in 2319 aluminium alloy via wire arc additive manufacturing coupled with multi-pass friction stir processing

The present study investigates the alterations in 2319 aluminium alloy microstructure and properties induced by the WAAM-FSP process, including grain size, microhardness and tensile strength. The effects of multiple stirring friction processing and remelting on the grains were systematically investigated. The results demonstrated that the grains within the stirring zone underwent enlargement due to thermal remelting, while the size of the stirring zone decreased. Furthermore, multiple thermo-mechanical factors significantly intensified grain growth in the bottom of the stirring zone, resulting in an increase of up to 3.4 μm.Upon a second remelting process conducted on the top of the sample, the grain size in the stirring zone can reach 3.7 μm. Additionally, the bottom stirring zone exhibited a higher prevalence of deformed grains (21.7 %) of deformed grains caused by the extrusion during multiple stirring friction processing. The top region was subjected to less thermo-mechanical influence, resulting in a smaller grain size and an ultimate tensile strength of 192.6 MPa and a hardness of 90 HV_0.2. This finding demonstrates highlights the impact of thermomechanical cycling on the grains within the multilayer samples prepared by the WAAM-FSP technique.