Influence of Si precipitates on fracture mechanisms of AlSi10Mg parts processed by Selective Laser Melting

Al alloy AlSi10Mg processed by Selective Laser Melting displays a very fine cellular eutetic microstructure (melt pool fine, MP fine) due to fast cooling rate from the melt. Such microstructural refinement results in high tensile strength and hardness. Studies have shown that a coarser cells region (melt pool coarse, MP coarse) as well as a heat affected zone (HAZ) can be observed at the melt pool boundary caused by a change of thermal history [1]. Those microstructural inhomogeneities act like a weak zone as demonstrated by the laser tracks observed on fracture features after tensile test [2]. This study aims at investigating in which zone fracture occurs. To do so, MP fine, MP coarse and HAZ were analyzed. Si precipitates spacing was compared with dimples size observed on fracture features. The Si precipitates fraction were quantified by image analysis. Hardness tests were performed in the 3 different zones by nanoindentation.

[1] Thijs et al., Acta Mater. 61 (2013) pp. 1809-1819
[2] Tang et al., JOM 69 (2017) pp. 516-522