Effect of TiB₂ Addition on Microstructure and Mechanical Properties of AA8009 Alloy Fabricated by Laser Additive Manufacturing

The research involves the addition of 5 vol.% TiB₂ particles into AA8009 alloy powder to synthesize TiB₂/AA8009 composite parts produced via laser powder bed fusion (LPBF). The addition of the TiB₂ particles causes the TiB₂/AA8009 composites with and without annealing have lower compressive strength than AA8009 alloy due to the change of the strengthening mechanism. The results further indicated that solid solution strengthening was the main strengthening mechanism of the LPBF AA8009 alloy at room temperature whereas Orowan strengthening became the primary strengthening factor after annealing at 673 K. In contrast, Orowan strengthening always remained the main strengthening mechanism for the TiB₂/AA8009 composite, irrespective of the annealing temperature. In addition, after annealing of the LPBF parts at 673 K, the compressive yield strength (CYS) of the unblended AA8009 alloy specimens had a ~ 2.5 times greater reduction (from 705 ± 16 to 459 ± 30 MPa) compared to that of the composite TiB₂/AA8009 samples (from 466 ± 23 to 368 ± 3 MPa). Therefore, TiB₂ particles can suppress the drop in yield strength of LPBF AA8009 alloy below 673 K, providing a theoretical and experimental basis for the applications of both LPBF AA8009 and TiB₂/AA8009 alloys at low and medium temperatures.