Effects of Al, Zn, and rare earth elements on flammability of magnesium alloys subjected to sonic burner–generated flame by Federal Aviation Administration standards

Abstract

Mg alloys are promising structural materials in aerospace industry due to high strength to weight ratio. However, most Mg alloys are limited in aircraft cabins due to their susceptibility to ignition and burning. To improve fire resistance, adding alloying elements is a strategy. Thus, the goal of this study is to explore the effects of alloying elements Al, Zn, and rare earths on Mg-alloy flammability by experiment, using the system and procedures in compliance with the Federal Aviation Administration (FAA) standards for Mg-alloy flammability test. Six commercial Mg alloys with different alloying elements (AZ91E, ZK61A, ZE63A, EZ33A, WE43B, and EV31A) were tested. Results indicate that Mg alloys with Al or Zn elements were of short ignition time and high weight loss. With rare earths, Mg-alloy flammability was suppressed obviously. It appears that this suppression effect with rare earth addition was attributed to the formation of protective oxide film on the surface of molten alloy. Further, a heat transfer model was established to analyze the temperature evolution of the test specimen subjected to the sonic burner–generated flame by FAA standards, and ignition temperatures of all testing Mg alloys were predicted based on the experimental ignition time. The predicted results confirm that with rare earths addition, ignition was delayed after melting by the protective oxide film formed on the surface of the molten alloy.