Influence of SLM scan-speed on microstructure, precipitation of Al3Sc particles and mechanical properties in Sc- and Zr-modified Al-Mg alloys

Additive processing via Selective Laser Melting (SLM) of Sc- and Zr-modified Al-Mg alloys (commercially known as Scalmalloy®) provides significant advantages over traditional 4xxx casting alloys. This is due to the high strength and ductility at very low mechanical anisotropy, which is a result of the alloys' very fine-grained microstructure combined with weak texture in the build-up direction. Next to their advantageous mechanical properties, the reliability of alloys processed by additive manufacturing is of great importance. Variations in microstructural features due to the use of different in processing parameters (e.g. laser scan speed) are well known for traditional alloys. This study analyses the influence of varying laser scan speeds on the static mechanical properties of SLM-processed Scalmalloy®, and discusses the evolving microstructure and precipitation of nm-sized Al3Sc particles at the correspondingly different energy inputs. It is found that by about doubling the laser scan speed the peak grain sizes in the fine-grained regions decrease from 1.1 μm to 600 nm, whereas in the coarse grained region almost no influence is observed. Al3Sc particles are only precipitated during processing at low scan speeds due to the corresponding high laser energy input, or by the intrinsic heat treatment from subsequent layers being built.