Influence of contouring on the microstructure and micromechanical properties of Laser Powder Bed Fusion (LPBF) processed Al6061 enhanced with reactive particles.

Age-hardenable aluminum alloys are of interest for powder bed fusion (PBF) additive manufacturing to produce lightweight, high-performance custom components. The successful processing of these alloys depends on specific alloying and print techniques to overcome defects that significantly degrade mechanical properties of PBF aluminum. The Reactive Additive Manufacturing (RAM) process modifieds alloy feedstock with reactive precursors which inoculate equiaxed microstructures during solidification, resulting in a reduction of columnar grain growth and shrinkage cracks. Additionally, surface quality is addressed by contouring, which retraces the perimeters of printed layers to produce smooth, fully fused surfaces. However, the combination of RAM and contouring methods has not been previously described in the literature, raising questions about the extent of refinement which is achieved when RAM particles are remelted by contouring laser sweeps. In this research, X-ray microcomputed tomography (XCT) was used to provide a complete characterization of RAM particles and defects in an AA6061-RAM alloy in 3D. The non-destructive XCT technique was used to quantify pore and particle distributions in the contoured alloy volumes and compared directly to hatched regions. The resulting three-dimensional analysis was correlated to traditional 2D microstructure quantification and nanoindentation experiments, providing a multimodal quantitative description of sub-micron grains, reaction products, and micromechanical properties. The study reveals that RAM particles inhibit cracking while simultaneously reducing the variance in mechanical properties between hatched and contoured regions of the build volume. • RAM particles and defects in an AA6061-RAM alloy were characterized in 3D. • Pore and particle distributions in the contoured and hatched regions were quantified. • RAM particles inhibit hot cracking while homogenizing mechanical properties in hatched and contoured regions. [ABSTRACT FROM AUTHOR]