Influence of Surface Tension and Evaporation on Melt Dynamics of Aluminum Alloys for Laser Powder Bed Fusion

One of the most important factors during Laser Powder Bed Fusion is a robust and stable process to generate reproducibly dense and crack-free components with the same homogenous and fine-grained microstructure. Among other factors, surface tension influences the robustness of this process. Three aluminum alloys were investigated by means of 3D laser printing with respect to their ability to form lightweight and high-performance structures. The alloys include two Al-Cr based alloys (Zicromal®: Al-Cr-Zr-Mn, Scancromal®: Al-Cr-Sc-Zr) and an Al-Mg based alloy (Scalmalloy®: Al-Mg-Sc-Mn-Zr). The surface tensions of their liquid melts were measured by means of the oscillating droplet method in electromagnetic levitation. Scalmalloy® exhibited a surface tension that was by 3-8% smaller than the other two alloys, over a temperature range of 500 K above their liquidus temperature; the evaporation analysis showed that Scancromal® exhibits significantly less evaporation compared to the other two alloys by an order of magnitude. During the Laser Powder Bed Fusion process, Scalmalloy® presented the most unstable melt dynamics, and Scancromal® appeared to be more robust and stable with less weld spatters and negligible dust deposition, as evidence from the high-speed video observations. The results support the idea that surface tension and evaporation are potentially crucial factors influencing the melt dynamics and also demonstrate the capability of additive manufacturing that produces customized aluminum alloys for aerospace applications.