EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Laser Powder-Bed Fusion (L-PBF) is an advanced additive manufacturing technique, which involves a complex multilayer micro welding process. Depending on the alloy selection and the welding mode, the results in printing high-density material could be significantly different, as the spatter formation and welding plume are interacting during the welding process that cause defects like gas pores, process pores, lack of fusion and so on. Previous studies inferred that the thermophysical properties might play an essential role in control of the manufacturing process, where melts with lower surface tension are easier to accelerate and form spatters (Felsing et al., J. Manuf. Mater. Process, 2019).
Thus, of particular importance is the understanding whether or how the surface tension will affect melt puddle dynamics and manipulate the printing results. Based on the tests among a batch of aluminum alloys for L-PBF, the Airbus new developed Zicromal® (Al-Cr-Zr-Mn) and Scancromal® (Al-Cr-Sc-Zr) are preferentially robust compared to the incumbent Scalmalloy® (Al-Mg-Sc-Zr) which includes low boiling point elements like Mg and is known to be also prone to oxidation.
The surface tension measurements of these three aluminum alloys melts were performed by oscillating droplet method using the electromagnetic levitation facility at DLR, to investigate the potential correlation between the surface tension of the melts and the performance of L-PBF. The results showed that the Al-Mg based alloy presents a slightly lower surface tension than the Al-Cr based alloys, which is less than 4% near to the melting point Tm ≈ 800 °C, and about 3% - 10% at higher temperature range near Tm+500 ≈ 1300 °C. However, because the difference of the measured surface tensions may not be significant enough to explain the observed alloy behaviors, obviously it still needs further investigations to conclude the role that the surface tension plays during the L-PBF process.