Magnesium alloy melt protection by high-efficiency phase transition of carbon dioxide

In this study, we developed and evaluated a highly efficient method for protecting magnesium melts by cooling and shielding the magnesium melt with carbon dioxide (CO₂) snow using a newly modified technique to achieve denser CO₂ snow than competing methods. Experiments, using a replicate CO₂ snow nozzle in Bach's study, were conducted for protection of the AZ91D alloy and pure magnesium in a 3-kg furnace to identify the protectiveness. The issue of CO₂ consumption was immediately apparent at the beginning of the phase-two tests using two Bach's nozzles. Hence, the modified denser CO₂ snow nozzle was designed and optimized to generate more dry ice. The optimized trigger mode to improve the efficiency of the dry ice manipulation was also proposed. Finally, a specialized pilot run of the protective system with the proposed denser CO₂ snow technique for a 200-kg melting furnace was developed and tested. This system had an excellent performance with a low CO₂ consumption of 1.2 kg/h for the AM60 magnesium alloy and demonstrated a quite low running cost of 0.55 USD/h compared with a non-denser CO₂ snow system. The proposed modified snow nozzle presents three major advantages: an improved cooling efficiency by almost 10 times, a longer lifetime for the solenoid valve, and a reduced need for furnace maintenance as a result of the sulfur-free operation.