Effect of powder-feeding process on metal transfer mode and microstructural evolution of wire–powder–arc directed energy deposition-manufactured aluminum alloys

Wire–powder–arc directed energy deposition (WPA-DED) technology offers significant potential for alloy development and the production of large, complex-graded material parts due to its capability for in situ deposit composition adjustment. However, the effect of the powder-feeding process on formation stability and microstructure development remains unclear. In this study, ER2024 wire and Al-4.44Cu-1.53Mg and Al-4.50Mg-0.65Sc-0.29Zr powders were used to form thin-wall samples. Quasi-static analysis of forces on molten droplets revealed that increased gas flow induced the formation of larger droplets. Infrared thermography identified changes in solidification conditions at different heights and gas flow rates, showing that lateral powder-feeding gas increased the horizontal temperature gradient at the molten pool’s top. This promoted horizontal columnar grain growth while suppressing vertical growth at the base, resulting in a bimodal microstructure. Applying columnar-to-equiaxed transition (CET) theory further showed that powders with heterogeneous nucleation elements refined the grain structure, yielding a uniform, fully equiaxed structure. These findings provide a basis for optimising WPA-DED processes and improving microstructural control and mechanical property.