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.