Effects of volumetric energy density on the microstructure of additively manufactured Scalmalloy

The parameters chosen in a laser powder bed fusion (LPBF) alloy build can drastically affect the resulting build microstructure. Aspects such as grain structure, precipitation, and porosity depend on the local thermal history during the build process and any post-build heat treatment the alloys may undergo. Scalmalloy is one such alloy produced via LPBF which displays the typical bimodal grain structure, with a mixture of primary and secondary precipitation, and multiple types of porosity. In the present study, three Scalmalloy samples produced with different values of volumetric energy density (VED) were investigated to gain further insight into build parameter and microstructure property relationships. Grain structures, elemental composition, texture, precipitation, and porosity were investigated. Key characteristics of the microstructure were studied at higher resolution and over larger areas than previously reported on, with the culmination of results intended to give a holistic view of the Scalmalloy LPBF microstructure. Results show an increase in fine grain proportion with increased volumetric energy density, with weak texture in coarse grains and no texture in fine grains. Samples were compositionally very homogeneous, with thermally stable microstructure, and contained multiple types of precipitates. When comparing between samples, those with the lowest value of volumetric energy density displayed the greatest porosity. LaserbeamFoam thermal-fluid-dynamics modelling showed the evolution of the melt pools with increasing VED, and supplements discussion on the increasing fraction of fine grains and the role of primary Al 3 (Sc,Zr) on fine grain nucleation.