The rupture zone in AlSi10Mg tensile specimen processed by selective laser melting is investigated. The microstructures at the melt pool boundary are analyzed. The Si phase fraction and the Si precipitate spacing are measured by image analysis and MEB-EDS analysis. Hardness tests are performed by nanoindentation. Fracture features are observed on broken samples. The Heat Affected Zone (HAZ) exhibits low hardness due to coarse non-coherent Si precipitates. This low hardness indicates that the HAZ is the preferential region where fracture is likely to occur. This is confirmed by Si precipitate spacing within the HAZ matching with dimple spacing observed in fracture surfaces. The amount of heat input can by controlled by tuning the process parameters so as to reduce the size of the HAZ and potentially improve the mechanical properties of the AlSi10Mg SLM parts.