Experimental and Numerical Investigation of an Overheated Aluminum Droplet Wetting a Zinc-Coated Steel Surface

Abstract

Wetting steel surfaces with liquid aluminum without the use of flux can be enabled by the presence of a zinc-coating. The mechanisms behind this effect are not yet fully understood. Research results on single aluminum droplets falling on commercial galvanized steel substrates revealed the good wetting capability of zinc coatings independently from the coating type. The final wetting angle and length are apparently linked to the time where zinc is liquefied during its contact with the overheated aluminum melt. This led to the assumption that the interaction is basically a fluid dynamic effect of liquid aluminum getting locally alloyed by zinc. A numerical model was developed to describe the transient behavior of droplet movement and mixing with the liquefied zinc layer to understand the spreading dynamics. The simulations reveal a displacement of the molten zinc after the impact of the droplet, which ultimately leads to an accumulation of zinc in the outer weld toe after solidification. The simulation approach neglects the effect of evaporating zinc, resulting in a slight overestimation of the final droplet width. However, in terms of spreading initiation during the first milliseconds, the simulation is in good correlation with experimental observations and demonstrates the reason for the good wetting in the presence of zinc coatings.

Numerical Study of the Effect of Workpiece Thickness on the Interfacial Behavior of a Molten Aluminum Droplet on a Zinc-coated Steel Sheet

“…Similar results were also expected based on numerical simulation [14]. Computational fluid dynamics (CFD) simulation results showed that molten zinc was laterally pushed as the molten metal propagated to the side.…”

“…Fig. 3 Comparison of the experimental (according to [14]) and simulation results (workpiece thickness: 0.8 mm).…”

“…Fig. 4 Molten droplet behavior on the workpiece (thickness: 0.8 mm, high speed video frames according to [14]).…”

Recent Advances in Study of Solid-Liquid Interfaces and Solidification of Metals

“…In the second article in this issue, Gatzen et al [2] utilized both experimental and numerical techniques to investigate the wetting process of an aluminum droplet on a zinc-coated steel surface. The final wetting angle and length were linked to the time where zinc was liquefied during its contact with the overheated aluminum melt, leading to the assumption that the interaction was basically a fluid dynamic effect of liquid aluminum getting locally alloyed by zinc.…”

“…The final wetting angle and length were linked to the time where zinc was liquefied during its contact with the overheated aluminum melt, leading to the assumption that the interaction was basically a fluid dynamic effect of liquid aluminum getting locally alloyed by zinc. To further investigate this process, Gatzen et al [2] developed a numerical model to describe the transient behavior of droplet movement and mixing with the liquefied zinc layer to understand the spreading dynamics. Their simulations revealed a displacement of the molten zinc after the impact of the droplet, which ultimately led to an accumulation of zinc in the outer weld toe after solidification.…”