A Mg-Al alloy was treated with gaseous carbon dioxide (CO2) and a refining process, and the grain refinement at each stage was investigated. The results indicated that CO2 and the subsequent refining process affect the grain refinement in the Mg-Al alloy. Moreover, the average grain size decreased from 254 to 89 µm, and the microhardness increased from 59.7 to 66.0 HV upon the addition of 9 litres of CO2. Increasing the time of the subsequent refining process to 30 min further decreased the grain size and increased the microhardness. Based on scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction analyses, the observed Al4C3 particles, which are attributed to the inoculation of CO2, are responsible for the grain refinement.
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