Improving density and strength-to-ductility ratio of a 3D-printed Al–Si alloy by high-pressure torsion

Abstract

Good combination of strength and ductility in metallic materials is always desired. To this end, this study assesses the combination of two modern manufacturing processes, namely additive manufacturing (AM) and severe plastic deformation, for an AlSi11Cu alloy. Laser powder bed fusion (L-PBF) produced an alloy with spherical pores with an average size of 42 μm, representing a volume fraction lower than 0.15%. At the mesoscale, the alloy showed a cellular microstructure made up of Al cells and Si-rich boundaries with an average size of 0.69 µm, which were broken down by the high-pressure torsion (HPT) process into ultrafine particles smaller than 0.41 µm. The HPT process transformed the columnar grains of the as-built material into ultrafine-grained grains around the disk edges, while the central zone conserved the as-built characteristics for a number of HPT turns smaller than ¼. HPT processing at room and warm temperatures gave rise to strength–ductility improvements with yield strengths and elongations larger than 400 MPa and 10%, respectively. The good strength–ductility trade-off was related to the porosity decrease, the breakdown of the interconnected network into particles of ultrafine size, the grain size reduction due to the dislocation density increase, and the formation of precipitates and Si-rich particles of different sizes. Thus, AM and HPT improved the grain boundary and precipitation strengthening, giving rise to an Al–Si alloy with superior mechanical properties.Graphical abstract