Thermodynamics of Phase Formation in Mg-Al-C Alloys Applied to Grain Refinement

Grain refinement of Mg-Al based alloys is challenging because it is known that Zr, which is extremely effective in many Al-free alloys, cannot be used. The addition of carbon through various routes by using carbon-containing sources is considered as an option. The grain refinement mechanisms are still under debate. The present work is focused on the ternary base system Mg-Al-C, including the potential nucleants Al4C3 and Al2MgC2, presently without consideration of Al2CO. The ternary carbide Al2MgC2 was synthesized and characterized using sealed Ta crucibles. The decomposition of the carbide was measured at 1290 degrees C by Differential Thermal Analysis under a pressure of 8 bar. Practical difficulties, including high vapor pressure of Mg and high affinity of Mg with oxygen, as well as rapid hydrolysis of the Al2MgC2 carbide have been overcome.