Effect of heat treatment patterns on porosity, microstructure, and mechanical properties of selective laser melted TiB2/Al–Si–Mg composite

Abstract

Selective laser melted (SLM-ed) pre-alloyed TiB2/Al–Si–Mg composite reports tremendous engineering application potential. However, systematic research on its heat treatment (HT) patterns is scarce. This paper utilizes direct aging (DA), annealing treatment (AT), and solution-aging treatment (SAT) to investigate porosity, microstructure, and mechanical properties. The porosities of as-deposited (AD), DA, and AT samples remained at <1.1%, while the nanopores at the molten pool boundary of AD sample expanded into the molten pool inner of DA and AT samples. For the condition SAT, the porosity exceeded 4.8% accompanied by large-sized micropores. Porosity development resulted from the entrapped hydrogen diffusion along the eutectic Si interface. The HT had little effect on the TiB2 particles and near-equiaxed grains. The eutectic networks of AD and DA samples broke into separate particles after the AT and transformed into coarser particles in the SAT sample. The nanoscale (Si + β′′) and β′ precipitates were exhibited for the DA and SAT samples, respectively, while there are also a few composite precipitates. The evolution of eutectic and precipitates was related to the diffusion of supersaturated solutes. Due to the significant contribution of Orowan strengthening (∼213.1 MPa), a superior combination of the ultimate tensile strength (∼521.6 MPa) and yield strength (∼389.9 MPa) was realized after the DA. The excellent elongation (∼19.3%) of AT sample was attributed to the eutectic spheroidization. However, the high porosity of SAT sample severely compromised mechanical properties. This work provides essential guidance for HT selection of SLM-ed particle-reinforced Al–Si–Mg composites.