A NEW TECHNIQUE TO MEASURE DYNAMICALLY THE SURFACE TENSION, VISCOSITY AND DENSITY OF MOLTEN METALS

摘要

A formulation is presented that enables the physical properties of melts to be measured using a new dynamic measuring technique. The surface tension, viscosity, and density are inherently part of an energy balance that characterizes flow rate through an orifice, subjected to the influence of gravity. The properties are determined from this relationship, which requires flow rate and head data, as well as knowledge of the frictional characteristics of the orifice. Experiments with molten aluminum in both argon and nitrogen atmospheres are presented at various temperatures and compared with literature. Results from AZ91D-alloy in argon are presented for the purpose of expanding the current knowledge of properties of magnesium-based systems. Experimental density measurements for aluminum and AZ91D agree well with relations established in the literature. The viscosity of aluminum varies little with temperature, which ranges between 4.89e~(-4)Ns/m~2 and 4.32e~(-4)Ns/m~2 at 700 deg C and 900 deg C respectively. For AZ91D, viscosity decreases sharply from the liquidus temperature and levels to approximately 3.0e~(-4)Ns/m~2 at temperatures greater than 700 deg C. The surface tension of AZ91D has been calculated to be approximately 10 percent higher than the case of pure magnesium. For aluminum, the outcome of the nitrogen trials indicates that surface tension is considerably higher than it is under argon atmospheres. The reasoning behind this is under investigation, however, it is strongly suspected that the difference is attributed to the formation of AlN at the melt-gas interface instead of Al_2O_3.