Rule of Alloy Design for Fire-Proof Mg Alloys

Fire-proof, fire-resistant or ignition-resistant Mg alloys require 2 important characteristics of no burning before the certain required period and self-extinguishment in the case of burning after the required time. This paper will discuss the nature of the surface oxide layer of Mg alloys to explain why conventional Mg alloys have no resistance of ignition and oxidize and burn so easily. The basic rule of alloy design for fire-proof Mg alloys will be addresses to form thin and stable surface oxide layer in terms of the following four categories – (1) lower oxide formation energy than MgO, (2) higher surface segregated tendency (larger Wigner-Seitz radius) than Mg, (3) PBR (Pilling-Bedworth) of oxides, and (4) melting points of unary and binary oxides. This paper will also discuss the invalidity of furnace chip test and the importance of DTA (Differential Thermal Analysis) as an academic and research tool to evaluate quantitatively the ignition temperatures of Mg alloys.

As one of potential fire-proof Mg alloys, the well-known ECO-Mg alloys will be presented, the results of which will be addressed by (1) artificial oxidation test, (2) DTA (Differential Thermal Analysis) of globular specimen, and (3) part fire test by LPG (Liquefied Petroleum Gas) and also (4) FAA standard fire test.

Besides of the improved fire resistance, ECO-Mg alloys are expected to reduce or eliminate SF₆ and SO₂ protective gases; eliminate Be addition; and improve melt cleanliness. Special attention is also paid to the improved melt cleanliness of ECO-Mg alloys not only for improved mechanical properties but also for enhanced castability and formability.