Material extrusion-based additive manufacturing of aluminum feedstocks with a focus on the debinding process

This study investigates the printability, debinding, and sinterability of aluminum-based (AA6061) feedstocks prepared with three different commercial thermoplastic binder compositions, with focus on the effect of the post-processing on microstructure and densification during sintering. Two debinding approaches were studied: (i) solvent debinding followed by thermal debinding, and (ii) single-step wick debinding, in which the green parts were embedded in a powder bed. Debinding is the most challenging stage for Al-containing feedstocks. The strong tendency of aluminum to oxidize significantly restricts the choice of solvent and limits debinding in an oxygen-containing atmosphere. To avoid oxidation of aluminum powder, the solvent type and debinding temperature in air must be restricted. This limitation can leave residues of carbon in the structure during sintering in a nitrogen atmosphere. Based on simultaneous thermal gravimetric analysis, the onset oxidation temperature for the 6061 aluminum powder used in this study was determined to be approximately 400 °C; therefore, the thermal debinding temperature under air was selected below this limit. The results showed that with both debinding methods, binder removal of ≥ 96% could be achieved. However, optical microscopy and density measurements after sintering indicated that even high-purity acetone as a solvent medium resulted in slight oxidation, particularly at the printed sample surfaces. Interestingly, wick debinding without previous solvent debinding resulted in samples with higher post-sintering density. The effect of sintering dwell time was also examined. Increasing the holding time from 2 h to 10 h improved the relative density from ~ 97% to ~ 98%.