Development of Ignition Resistant Mg: The Effect of Heating Rate on the Ignition-Resistance of Mg-Sr Alloys

It is found that the ignition resistance of magnesium-alkaline earth alloys is influenced by heating rate to the ignition temperature. In this study, a series of Mg-Sr alloys (Mg-1.1Sr, Mg-1.5Sr, Mg-2.14Sr, and Mg-2.4Sr) is tested using two different heating rates. The results indicate that Mg-Sr alloys exhibit different ignition behavior and ignition temperature that are determined by the heating rate. Samples heated using a high heating rate ignite close to the melting temperature of each alloy. When a low heating rate is used, the ignition temperature increases by 100 - 150 °C. The low heating rate extends the semi-solid state, where the Sr-rich molten pools promote the development of a thin and protective oxide scale, thanks to the surface-active behavior of Sr. During high-rate heating, the semi-solid-state formation of the liquid pools is limited, and the oxide scale grows laterally from the solid interdendritic region, becoming thicker and generating internal stresses. When the liquid state is reached, and the oxide scale fails; molten Mg is exposed to the atmosphere with consequential ignition.