Evaluation of Microstructures and Hardness of Al-10Si-0.45Mg-0.4Sc Alloy Powders

There is continuing interest to develop lightweight and strong alloys for the aerospace sector. The advent of 3D printing has spurred a search for alloys developed for these processes. One such alloy of interest is the Al–10 wt%Si–0.45 wt%Mg–0.4 wt%Sc that has been developed and used in laser powder bed 3D printing. This study is focused on characterizing the microstructures of the atomized Al-10 wt%Si–0.45 wt%Mg–0.4 wt%Sc alloy to provide a basis for understanding the microstructural evolution of this alloy during processing. The atomized powders were separated into four size ranges. Each range was quantitatively characterized by determining its dendritic length scale and hardness. Mean spacing values from 1.5 μm to 5.5 μm could be associated with hardnesses from 105 HV to 120 HV, with higher hardness related to lower spacing. The 3D Si growth morphologies were found to fall into two distinct groupings. The first was a mixture of skeletal Si plates and in-plane Si rods for the largest particle sizes. The second grouping was related more specifically to powders with <125 μm in size. A prevalence of Si fibers was noted for this specific group. These observations were compared to those of previous works performed on eutectic morphologies of Al–Si and Al–Si–Mg alloys.