Pieces of AZ61A cakes were heated and combusted by the flame of a torch. The progressive development of heated cake was recorded and described. The product of Mg(OH)2 covers on the surface of heated AZ61A cake and protects it from oxidation. Reactions of Mg(OH)2→MgO+H2O, and 2Mg+CO2→2MgO+C occurred during heating by flame and after AZ61A melted. The continuously oozed out molten metal produced MgO and released a great amount of heat to react with carbon film. This led to the reaction of MgO+C→Mg+CO and the product of Mg carried out oxidation and formed MgO. The residual showed that all AZ61A completely burned out and became a mess of white powder. Pieces of AZ61A cakes were also set on the specimen holder in the designed containers. The difference of responded temperatures from specimen holders (one was with AZ61A cake; another was without AZ61A cake) was recorded and analyzed. Mechanisms for illustrating the reaction of Mg with different gases (air, CO2 and different ratios of CO2/Ar) were schematically illustrated. Possible reactions of Mg and O2, CO2 and CO were also discussed in this study.