Microstructure of Additively Manufactured Al Alloys Effects the as-Built Mechanical Properties

Isotropic mechanical properties of Al alloys remain a challenge of L-PBF due to the effects of epitaxial growth, rapid cooling, and reheating cycles on the microstructure. In this study the microstructure and mechanical properties of two different Al alloys are investigated. AlSi10Mg, known to produce columnar grains, is compared directly with a high Scandium Al-Mg alloy, which produces an equiaxed microstructure. The microstructure of the as-built samples were characterised using X-ray diffraction (XRD), electron back scattered diffraction (EBSD), tensile testing and Vickers hardness testing. The study showed that the maximum tensile strength of the fine equiaxed grain structure produced by the high Scandium Al-Mg alloy was lower when compared to that of the columnar grained AlSi10Mg, indicating that the equiaxed grain structure does not produce enhanced mechanical properties in the as-built condition. This indicates that post processing heat treatments are necessary in order to achieve the highest mechanical properties not just a fine grain structure alone. It was confirmed that the equiaxed grain structure does prevent isotropic mechanical properties as the Scandium Al-Mg alloy had similar tensile strengths regardless of the print orientation compared to the columnar AlSi10Mg having a lower tensile strength in the case where the parts were printed perpendicular to the build plate.