The Surface Tension of Pure Aluminum and Aluminum Alloys

The surface tension of high purity and commercial purity aluminum in vacuo was determined using the sessile drop method and the results were found to compare favorably with published data. The effects of holding atmosphere, substrate, and “surface fracture” of the sessile drop on the measured surface tension values were investigated together with the effects of different solute elements commonly present in commercial aluminum alloys. The results obtained suggest that the nature of the surface oxide film formed on the droplets (affected by alloy composition and atmosphere) and the rupture of this film are the dominant factors influencing the surface tension values obtained. Changes in surface tension values of up to 60 pct were observed. The possible effect of this variable surface tension on practical casting processes, such as direct chill casting, is suggested.