Improvement of grain refining efficiency for Mg–Al alloy modified by the combination of carbon and calcium

The effects of carbon and/or Ca on the grain refinement of the Mg–3Al alloy have been investigated in the present study. The grain size of the Mg–3Al alloy decreased steeply with increasing the Ca content when it was lower than 0.2%. And then, the grain size decreased slightly when the Ca content was increased to 0.5%. A remarkable grain refining efficiency could be obtained for the Mg–3Al alloy treated with only carbon. Further high grain refining efficiency could be obtained by the combination of 0.2%C and the optimal content (0.2%) of Ca. Therefore, Ca is an effective element to improve the grain refining efficiency for the Mg–Al alloys refined by carbon. The AlCO particles were observed in the samples refined whether by only 0.2%C or by the combination of 0.2%C and a little (less than 0.2%) Ca addition. These AlCO particles should be the potent nuclei for the Mg grains. However, the AlCOCa intermetallic particles were observed when Ca content was increased to 0.5%. Peculiar particles with duplex phases were found in this sample in such a state that AlCO coating film was formed on the surface of Al–Ca compounds. These particles should also be the potent nuclei for the Mg grains.