Development and validation of a new methodology for determining the rheological behaviour of low melting point alloys

Although liquid metals have long been considered Newtonian fluids, recent studies suggest that their rheological behaviour may be significantly more complex. Under certain conditions, they exhibit non-Newtonian characteristics. Accurate rheological characterisation of these systems is essential given their widespread use in industries such as electronics, energy and advanced manufacturing. A major challenge when studying molten metals is their high reactivity with oxygen, which leads to the rapid formation of oxide films that alter measured viscosity values and obscure intrinsic flow behaviour. In this study, we present a simple, cost-effective and environmentally friendly methodology for characterising the rheological properties of low melting point metal alloys using a standard rotational rheometer with a concentric cylinder geometry. Using technical-grade glycerine as a protective and reducing medium significantly reduces the effects of oxidation during measurement, eliminating the need for expensive inert gas environments. We demonstrate this approach using Bi-Pb-Sn, Bi-Pb, Bi-Sn and Ga-In-Sn alloys and show that the technique can reliably detect apparent viscosity values in the single-digit mPa·s range. The methodology also enables the identification of shear rate plateaus, which is essential for determining whether the system exhibits Newtonian or non-Newtonian behaviour. Our results demonstrate that even minor oxidation can have a significant impact on rheological data, emphasising the importance of effective surface protection. This work provides a practical tool for studying liquid metals and supports a broader re-evaluation of their flow characteristics.