Microstructural investigation and mechanical behavior of a two-material component fabricated through selective laser melting of AlSi10Mg on an Al-Cu-Ni-Fe-Mg cast alloy substrate

Abstract

A hybrid-part made of two materials was fabricated by selective laser melting (SLM) of AlSi10Mg on an Al-Cu-Ni-Fe-Mg cast alloy substrate. The microstructure of the two-material component and the interface is investigated using multi-scale characterization techniques including optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). The microstructure of SLM-AlSi10Mg consists of fine cellular dendrites and columnar grains, developed along the building direction, where the substrate cast alloy is featured by large equiaxed grains. OM and SEM studies of the interface show a sound metallurgical bonding as a result of the melting of AlSi10Mg powder and partial melting of the cast substrate assisted by the circulate flows and Marangoni convection. The circulate flows cause complex phenomena at the interface, which lead to the dilution of alloying elements and a variation in the microstructure of the first consolidated layer of SLM-AlSi10Mg (as a result of variation in thermal gradient and solidification rate). TEM investigations of the interface reveal segregation of alloying elements at the interdendritic regions after solidification. Moreover, no precipitate is formed on top of the interface, due to the rapid solidification and dilution of the alloying elements. EBSD analysis of the interface shows substantial differences in the grain structure of SLM-AlSi10Mg and the cast substrate, in terms of size and morphology. Mechanical properties of the hybrid material are studied afterwards using Vickers microhardness measurements, nanoindentation and quasi-static uniaxial tensile tests. The SLM-AlSi10Mg side of the hybrid-part possesses better performance, mainly due to its finer and hierarchical microstructure.