The Surface Tension of Molten Aluminum and AI-Si-Mg Alloy under Vacuum and Hydrogen Atmospheres

The surface tensions of pure molten aluminum, A356 alloy (Al-7 pct Si-0.3 pct Mg), and strontiummodified A356 alloy have been measured under vacuum and hydrogen atmospheres using the sessile drop technique. The values obtained for pure aluminum at 680 °C and for A356 alloy and modified A356 alloy at 630 °C are 1.007, 0.889, and 0.844 N/m, respectively, when measured under vacuum. The addition of hydrogen gas to the atmosphere of the liquid droplet has no significant effect on the surface tension of the unmodified A356 alloy, while it lowers the surface tension of the modified alloy to 0.801 N/m. This effect is possibly due to the formation of SrH(2).