Mechanical Anisotropy Investigated in the Complex SLM‐Processed Sc‐ and Zr‐Modified Al–Mg Alloy Microstructure

Abstract

Additive manufactured Sc-modified aluminum alloys hold great promise for aerospace components under high and/or complex loads. While the thermal patterns formed in the melt pool during selective laser melting (SLM) of the powdered material result in a complex microstructure featuring a bimodal grain size distribution, such alloys show an isotropic mechanical response during mm-scale testing. To understand the role of microstructure on the mechanical response, nanoindentation is performed on SLM-processed Scalmalloy 1 for both the untreated and precipitate-hardened alloy, studied both parallel and orthogonal to the build direction. The elastic modulus of the coarse and fine grained regions is significantly greater than the macro-scale modulus of the material, suggesting macroscopic control over the elastic performance. With negligible influence over the elastic properties, there is a significant correlation between the grain size distribution and the nanoindentation hardness. This weak but significant grain boundary strengthening is lost when applying load orthogonal to the build direction for the precipitate-hardened material. Hardness anisotropy is moreover observed in fine-grained regions for the as-processed sample. In contrast to the isotropy reported from larger-scale mechanical tests, the discrete microstructural zones deviate from ideal isotropic behavior, and this may have consequences for simulation and design of this alloy.

An Investigation of the Influence of Changing Energy Volume Densities to Produce a Complete Process Parameter Window for Selective Laser Melting of Scalmalloy

“…To investigate a complete SLM processing window for relative densities exceeding 99%, a second build job will be performed with differing energy volume densities and respective scan speeds of 30, 45, 60, 80, 100 J/mm3 and 2962, 1975, 1481, 1111, 889 For each of the five sets of SLM process parameters, one cube sample on 3mm high support structures were built (figure 1), whereby 5 cube samples were built in one build job. Anisotropy is not investigated in this paper as both Schmidtke et al (2011) and Best et al, (2018) have indicated that anisotropy is very low for Scalmalloy, therefore all samples were built in a line parallel to x-direction with 20mm distances in between each cube and centered on the build platform.…”

“…Lastly, a hyper eutectic Al-Sc composition was attained. Best et al (2018) studied the mechanical anisotropy for the bi-modal microstructure of Scalmalloy. Anisotropy was low on a macroscopic scale, and although some microscopic discrepancies were found, these could be improved with annealing further supporting 1 st ICESET 2020 23 Schmidtke et al (2011) findings.…”

Microstructure Evolution and Mechanical Property Response of 3D-Printed Scalmalloy with Different Heat-Treatment Times at 325 °C

“…For example, compared with the samples fabricated by the casting process, the Al-0.5% Sc alloy fabricated by SLM exhibits a finer grain size and better mechanical properties, and with the average grain size decreased from 25 to 7 µm, the yield stress has been increased from 131 to 323 MPa, and the elongation has been increased from 3.7 to 10.5%, respectively [22]. Moreover, the grain size and microstructure feature could be altered by changing the 3D printing parameter and thus the mechanical properties of the 3D-printed materials could be affected [20,[23][24][25][26][27]. In our previous study, we showed that the grain size can be reduced and the columnar grain can be limited by adjusting parameters and thus significantly improve the yield stress and elongation of the 3D-printed Scalmalloy [19].…”