Unforeseen precipitation sequences in ex-situ/in-situ TiB2-reinforced Al2618 Composites Manufactured by Laser-based powder bed fusion

This study explores an innovative hybrid approach for the fabrication of metal matrix composite powder feedstock consisting of Al2618 alloy reinforced with TiB 2 . The approach combines pre-alloyed Al2618 powder containing Ti and B to form in-situ TiB 2 with high-energy mechanical mixing to disperse ex-situ TiB 2 on particle surfaces. The feedstock was processed via powder bed fusion - laser beam of metals and subjected to T5 and T6 heat treatments. Microstructural investigations revealed deviations from the typical precipitation and dissolution sequences of conventional Al2618 alloys, attributed to the excess Ti in the pre-alloyed powder, which largely influence the mechanical and physical properties of the material. T5 promoted Al 3 Ti and S/S′ precipitates near cell boundaries, leading to UTS and YS of 459 and 433 MPa. T6 produced Ti–Si–rich needle-like phases and Al–Mg–Ti particles that suppressed S′ precipitation. T6 showed the lowest thermal expansion and highest thermal conductivity, attributed to coarser Al 9 FeNi precipitates and dissolution of the cellular microstructure. The elastic modulus reached 84.7 GPa (T5) and 82.2 GPa (T6), about 13 % higher than standard Al2618. • Hybrid method enables high TiB 2 loading in Al2618 via powder surface functionalization. • Nanometric TiB 2 suppresses columnar grain growth in PBF-LB/M processed material. • Excess in Ti leads to unforeseen precipitation sequences in 2618 Al alloy. • T5 heat treatment yields highest tensile and yield strength via Al 3 Ti, S′ precipitates. • T6 treatment improves thermal stability through Ti–Si-rich needle-like phase formation.