Feasibility study on air-exposed debinding and sintering of aluminum parts fabricated by material extrusion (MEX) additive manufacturing

Metal additive manufacturing (MAM) enables cost-effective, sustainable production of complex components. Among its techniques, metal material extrusion (MEX) is attractive due to its simplicity, safety, and lower cost than laser-based or vacuum-assisted methods. However, sintering MEX-fabricated aluminum is challenging because rapid alumina formation hinders particle bonding and densification. This study investigates how heating rate, thermal-debinding soaking time, sintering temperature, and sintering time affect microstructure, EDS oxygen signal, porosity, apparent (Archimedes) density, and hardness of pure aluminum parts processed in air. A design of experiments (DOE) framework was used as a screening study to evaluate main effects; interaction effects are not fully decoupled and results are interpreted within this limitation. Heating rate and sintering temperature showed the strongest contributions to the EDS oxygen signal, while sintering time mainly affected hardness and densification. Soaking time had the highest contribution to porosity, though only slightly higher than the other factors. A moderate heating rate (5 °C/min) and intermediate sintering temperature (930 °C) yielded the lowest mean porosity (∼38%) and a more uniform microstructure. A higher sintering temperature (1030 °C) increased the temperature-level mean hardness (24.6 HV) along with a higher EDS oxygen signal. Overall, the results suggest that thermal management can partially mitigate oxide pinning via diffusion-controlled neck growth and Kirkendall-type pore evolution, enabling controllable porosity and improved bonding even in air. These findings clarify process-structure-property relationships in MEX aluminum and support practical, low-cost sintering protocols for sustainable metal AM.