Phase transformation and thermal analysis during combustion synthesis of Mg₁₇Al₁₂ alloy

The Mg-Al hydrogen storage alloy was successfully prepared by combustion synthesis (CS) method. The formation of alloy phases during the CS process was studied using X-ray diffraction (XRD), scanning electron microscope (SEM), and differential scanning calorimetry (DSC). When the time increases from 0, 0.5, 1.0 to 2.0 h at 733 K, the products are Mg and Al; Mg₂Al₃, Mg and Al; Mg₁₇Al₁₂, Mg₂Al₃; and Mg; and eventually only Mg₁₇Al₁₂, respectively. Combined with three peaks in the DSC traces, it is concluded that the formation of Mg₁₇Al₁₂ during the CS includes three processes, namely, the formation of Mg₂Al₃ first; then the unsaturated solid solution, Mg₁₇Al₁₂; and finally the complete Mg ₁₇Al₁₂ alloy. The formation of Mg₂Al ₃ prior to Mg₁₇Al₁₂ in this work is different from those prepared by mechanical alloying. This is thought to be related to the instant high temperature during the thermal explosion of CS.