Influence of Al and Y on the ignition and flammability of Mg alloys

The influence of alloying on the ignition and flammability was studied. One end of a cylindrical specimen was exposed to a free diffusion flame. Ignition required at least partial melting. Burning extinguished once the flame was withdrawn. Specimen tips of pure Mg, AZ61, and AZ91 ignited upon prolonged flame exposure. There was smouldering and delayed ignition for Mg-1Y. There was no ignition for Mg-5Y specimen tips, attributed to a protective surface oxide containing Y. The results indicate that (i) vigorous burning requires a continued supply of Mg vapour, and (ii) a critical alloy concentration is required to change ignition behaviour.

► Ignition occurred only after melting for high purity (HP) Mg, AZ61 and AZ91.
► Burning of specimen tips extinguishing for HP Mg, AZ61 and AZ91.
► Small molten blobs of HP Mg, AZ61 and AZ91 continued to burn.
► There was no ignition for Mg-5Y specimens.
► The higher ignition resistance of Mg-5Y is attributed to a more protective oxide.