Effect of silicon content on densification, mechanical and thermal properties of Al-xSi binary alloys fabricated using selective laser melting

The effect of the silicon content on the densification of Al-xSi binary alloys (x=0, 1, 4, 7, 10, 12, and 20 mass%) fabricated using selective laser melting (SLM) were systematically studied. By optimizing laser scanning parameters for each Al-xSi powder, almost fully dense SLM samples (more than 99.5% relative density) could be achieved for the Al-0Si (pure aluminum), and Al-4-20Si alloys. The Al-1Si SLM sample, on the other hand, contained many microcracks, considered to be solidification cracks. The Al-1Si SLM sample, in the solid-liquid coexisting state, was brittle and no healing of the cracks by the infiltration of the liquid phase occurred. Therefore, the cracks were easily generated due to thermally induced tensile stresses during solidification. The microstructures and the mechanical and thermal properties of the Al-xSi SLM samples fabricated using the optimal laser scanning parameters were examined. As the silicon content increased, the ultimate tensile strength and proof stress increased, whereas the elongation and thermal conductivity decreased. These mechanical properties were attributed to larger amounts of the crystalized phases of silicon (obstacles for the movement of dislocations) with increasing silicon content. The crystalized phases can also scatter conduction electrons, thereby decreasing the thermal conductivity.