Additively Manufactured Al-Mg-Ca-Sc Alloy with Hierarchical Microstructure: Strong and Ductile at Both Room and Elevated Temperatures

Abstract

An Al-Mg-Ca-Sc alloy with low hot cracking susceptibility was designed and fabricated by selective laser melting technology. A hierarchical microstructure, i.e., solute Mg, dispersed nanoscale Al3(Sc, Zr) precipitates in the grains and a semi-network of Al4Ca eutectic phases along grain boundaries, was built. The mechanical properties of the additively manufactured alloy showed superior strength and ductility at room temperature compared with the cast alloy arisen from the fine microstructure and a high fraction of the strength was retained at elevated temperatures due to the high thermal stability of nano-precipitates and grain boundaries when compared with the additively manufactured AlSi10Mg and Scalmalloy® alloys and the cast Al-Mg-Ca-Sc alloy. An analysis of strengthening mechanisms revealed that the grain boundary strengthening contributes most to the yield strength, followed by particle strengthening and solid solution strengthening. Ab initio calculations revealed a strong grain boundary segregation tendency for Ca, whereas the segregation tendency was weak for other elements, unraveling the origin of the hierarchical microstructure. Moreover, the evaluation of embrittlement potency showed that the segregation of Ca at grain boundaries does not cause grain boundary embrittlement, consistent with the measured high ductility.

Keywords: Additive Manufacturing, Aluminum alloys, Hierarchical microstructure, Mechanical properties, Ab initio calculations