Selective laser melting of AlCu-TiB2 alloy using pulsed wave laser emission mode: processability, microstructure and mechanical properties

Abstract

The present work explores the processability of an advanced aluminum alloy, namely AlCu-TiB2, by selective laser melting (SLM), and the correlation between microstructure and mechanical properties of as built specimens. The principal process parameters of the laser emission in pulsed wave (PW) mode, namely laser power and exposure time, were varied to achieve full density parts starting from prealloyed powders. Detailed analysis of defects in the highest relative density conditions was performed thzrough X-ray computed tomography. It was found that the highest relative density, up to 99.5%, was achieved at a laser energy density of 82 J/mm3. Microstructure of as-built specimens was analyzed through scanning electron microscopy, coupled with EDX and EBSD analyses, and transmission electron microscopy. The as-built microstructure was considerably uniform, and characterized by fine equiaxed grains, decorated with micrometric and nanometric second phases and an even distribution of reinforcing TiB2 particles; no epitaxial grain growth was observed. Finally, tensile behaviour of the as-built specimens indicates a yield and ultimate tensile stress of 325 MPa and 395 MPa, respectively, combined with an elongation of 13%. The low work hardening rate and jerky flow characterizing plastic deformation are analyzed and discussed.