Composition-dependent solidification cracking of aluminum-silicon alloys during laser powder bed fusion

Consistent manufacturing of volumetrically dense engineering components, free of solidification cracks by laser powder bed fusion (LPBF), has been demonstrated for Al-Si alloys such as AlSi10Mg and Al12Si. The success in LPBF of these alloys is attributed to the near eutectic composition with a small freezing range. To illuminate this observation, cracking susceptibility was examined from Scheil-Gulliver solidification modeling by calculating the hot cracking susceptibility, vertical bar dT/df(S)(1/2)vertical bar. To validate the findings from hot cracking susceptibility calculations, six binary Al-Si alloys, whose compositions were strategically chosen at hypo-, near-, and hyper-eutectic compositions, were gas atomized into alloy powders, and processed by LPBF. Only Al-Si alloys with 1.0 and 2.0 wt.% Si were found to exhibit cracking, which was predicted by relatively large magnitudes of vertical bar dT/df(S)(1/2)vertical bar. Either as particles or with a eutectic structure, Si segregation at the intercellular boundaries was observed to define the sub-grain cellular structure. For selected compositions, measurement of the cellular structure allowed for estimation of the cooling rate to be 10(6) to 10(7) K.s(-1). Excluding the alloys with solidification cracking, an increase in tensile strength and the corresponding decrease in ductility were observed with an increase in Si concentration, which were attributed to the formation of a cellular structure and the amount of Al-Si eutectic found at the intercellular boundaries. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd.

Automated summary

The successful manufacturing of volumetrically dense engineering components free of solidification cracks by laser powder bed fusion (LPBF) has been demonstrated for Al-Si alloys such as AlSi10Mg and Al12Si. The study found cracking susceptibility in Al-Si alloys with 1.0 and 2.0 wt.% Si, attributed to relatively large magnitudes of vertical bar dT/df(S)(1/2)vertical bar. Si segregation at the intercellular boundaries and the formation of a cellular structure were observed, allowing for estimation of the cooling rate.