Thermodynamic and kinetics investigation of elemental evaporation from molten Al7Si4Cu alloy

Abstract

Treatment of liquid aluminum alloys in low vacuum conditions is often applied for parts production in the automotive and aerospace industry because of its effectiveness in removing dissolved gases. Because of the low vapour pressure of aluminum, concentrations of the most unwanted elements can be significantly reduced at lower pressures. Presented work analyzing kinetics parameters for elemental evaporation from liquid Al7Si4Cu alloy. The pressure inside mullite refractory material was below 2.1 kPa for melt temperatures between 760 and 910 °C. The alloy’s chemical composition was characterized by the Inductively Coupled Plasma Mass Spectrometry method. Lead, Zinc, and Mercury were reduced at the highest rate while the lowest evaporation occurred for key alloying elements such as Silicon and Copper. Higher evaporation rates were achieved at higher temperatures. The evaporation ratios, volatility coefficients, reaction rate constants, mass transfer coefficients, and elemental evaporation susceptibility on temperature increase were deduced for 16 elements. The obtained results confirmed that keeping molten aluminum alloys in low vacuum conditions for one hour is an efficient method in removing unwanted elements with great potential for further improvement in industrial conditions.