Effect of Initial Relative Density on Liquid-Phase Sintering Behaviors of Al Powder Using Al–Cu Eutectic Alloy Aid: In Situ Observations Using Tomography and Microscopy

Aluminum (Al) powder with low sinterability is difficult to use in binder jetting (BJT) additive manufacturing, which involves sintering a metal powder after forming a green body. A liquid-phase sintering process for Al powder using Al-Cu eutectic alloy powder as a sintering aid has recently been developed. In this study, to clarify the applicability of liquid-phase sintering to BJT additive manufacturing, the effect of the initial relative density of green bodies (<i>ρ</i>_rel,0 = 50-90%) on the final relative density was investigated. The final relative density was not significantly affected by <i>ρ</i>_rel,0 and achieved 96-97% after sintering at 630 °C for 1800 s. However, pores are likely to remain in the sintered body with a high <i>ρ</i>_rel,0 of 90%. In situ observations using synchrotron radiation X-ray computed tomography revealed that large pores were formed at the early sintering stage of the green body with <i>ρ</i>_rel,0 of 90% and partially retained after sintering. By contrast, the green body with <i>ρ</i>_rel,0 of 50% exhibited a significant rearrangement at the early sintering stage, promoting the densification. This study provides a deep understanding of liquid-phase sintering of Al powder, which is considered a suitable post-processing method for BJT additive manufacturing.