Effect of initial temperature on actual elemental evaporation rate in Al-Si-Cu mixture during free cooling in near-vacuum conditions

Freezing aluminum alloys in vacuum conditions could be an effective method to improve its chemical composition. Aluminum has a lower vapour pressure than most unwanted elements while values for major alloying elements are significantly below the corresponding aluminum vapour pressure curve. Here we formalize and calculate parameters for the elemental evaporation rate constants in the freezing Al-Si-Cu system. The highest evaporations were measured for Hg, Zn and Pb while no elemental losses for Si, Cu or Ni were recorded for temperatures below 760 °C. Notwithstanding the known positive effect on mechanical properties, freezing aluminum based mixtures from 760 °C in near-vacuum conditions can significantly reduce concentrations of most unwanted elements without affecting established procedures and capacities.