Nanoscale Al precipitation in the Si phase in AlSi10Mg alloy during electron beam powder bed fusion

Additive manufacturing of Al alloys has garnered attention in the aerospace and automobile industries. This is the first study on the formation of nanoscale Al precipitates in the Si phase of an AlSi10Mg alloy during electron beam powder bed fusion (EB-PBF). Spherical Si particles were homogeneously dispersed in the Al matrix, highlighting the difference from the laser beam PBF (LB-PBF) microstructures. Nanoscale Al phase was formed with a crystallographic orientation relationship with the surrounding Si phase: (111)_Si//(111)_Al and [1$\overline{1}$0]_Si//[1$\overline{1}$0]_Al. The formation of Al nanoprecipitates was attributed to an interplay between non-equilibrium solidification, wherein excess Al was dissolved in the Si particles, and the subsequent decomposition of the supersaturated Si phase during high-temperature exposure owing to the preheating procedure. To the best of our knowledge, such formation of Al nanoparticles has not been reported in AlSi10Mg produced through conventional processing or LB-PBF. Thus, the unique thermal history of EB-PBF provides novel opportunities for microstructural evolution, which may be beneficial for the development of novel Al-based alloys.