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 TiB2. The approach combines pre-alloyed Al2618 powder containing Ti and B to form in-situ TiB2 with high-energy mechanical mixing to disperse ex-situ TiB2 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 Al3Ti 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 Al9FeNi 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.