Effects of gravity on the capillary flow of a molten metal

Repair and construction in space by means of brazing requires understanding of the effect of gravity on the capillary flow of a molten metal. We perform two sets of experiments: (1) spreading of a sessile drop of liquid aluminum-silicon-flux (Al-Si-KxAlyFz) composite braze on a horizontal alumina (Al2O3) substrate (a non-wetting surface), and (2) capillary flow of the same braze alloy on an inclined aluminum-manganese (AA3003) substrate (a wetting surface). We vary the mass of the brazing liquid and the inclination of the substrate (i.e., the relative direction of gravity).In the composite metal/flux sessile drop experiments, we observe a secondary liquid flux meniscus forming at the contact line between the liquid Al-Si and the alumina substrate. We demonstrate that the equilibrium contact angle appears to be close to 180 degrees, while the apparent contact angle depends on the mass of the braze. In the second set of experiments, we study the molten braze alloy on different inclinations of AA3003 in a wedge-T wetting/non-wetting assembly. As the inclination angle decreases, the wetting distance increases and the sur-face profile changes from a non-symmetric bag-like shape to a more symmetric pancake shape. With the mass decreasing, the surface profile on the vertical substrate approaches a symmetric shape when the wetting distance is equal or smaller than the capillary length. While the non-homogeneous melting and hence, the non -homogeneous microstructure of the melt, may prevent a full symmetry. Computational predictions of equilib-rium shapes are in good agreement with experimental results.

Automated summary

Understanding the effect of gravity on the capillary flow of molten metal is crucial for repair and construction in space through brazing. Our experiments demonstrate the formation of a secondary liquid flux meniscus in contact between liquid Al-Si and an alumina substrate. The equilibrium contact angle is close to 180 degrees, while the apparent contact angle depends on the brazing liquid mass. Additionally, the surface profile of the molten braze alloy on inclined AA3003 changes from a non-symmetric shape to a more symmetric shape as the inclination angle decreases.