Effect of heat treatment on SLM-fabricated TiN/AlSi10Mg composites: Microstructural evolution and mechanical properties

This paper systematically investigates the effect of artificial aging (AA), solution (SHT), and T6-like (solution followed by artificial aging (SHA)) heat treatments on the microstructural evolution and mechanical properties of selective laser melted TiN/AlSi10Mg composites. Results show that the microstructure and mechanical properties reveal inconspicuous changes after AA where the eutectic fibrous Si networks remain. However, SHT vanishes the Si networks, precipitates and coarsens Si particles, and eventually softens the Al matrix, leading to a significant decrease in tensile strength and hardness of heat-treated composites and an increase in ductility. The addition of TiN nanoparticles plays a significant role in microstructural evolution during heat treatment. By increasing solution temperature from 460 °C to 540 °C, Mg2Si phase precipitates out of the Al matrix, followed by AlFeSi intermetallic at 500 °C and AlSiTi intermetallic at 540 °C, respectively. Interestingly, unexpected enhancements of hardness (from 91.5 ± 2.3 HV to 105.9 ± 2.1 HV) and tensile strength (from 268.7 ± 2.5 MPa to 336.8 ± 1.5 MPa) are achieved as the solution temperature increases. This abnormal phenomenon is attributed to the precipitation hardening by the Mg2Si precipitate and needle-like intermetallics, which overcomes the effects of microstructural coarsening and matrix softening. This paper sheds light on how the mechanical properties of as-built TiN/AlSi10Mg composites can be tailored using different heat treatment techniques. •TiN/AlSi10Mg composites are fabricated by SLM and then heat treated.•The AlFeSi and AlSiTi intermetallics are formed at different solution temperatures.•The unexpected increase of hardness and strength is attributed to precipitate hardening.•The mechanical properties are found to be highly microstructural-dependent.