The effect of iron on the grain refinement of Mg-3Al alloy modified with and without carbon powder has been investigated in the present study. Significant grain refinement could be obtained for Mg-3mass%Al alloy modified with either Fe or carbon. The Al-C-O and Al-Fe particles were observed which should be the potent nuclei for Mg grains. The high segregating power of Fe was also proved as an important factor which determines the grain size of Mg-Al alloys. Refining efficiency could be further obtained by the combination of Fe and carbon. Both Al-C-O-Fe-rich and Al-Fe-rich intermetallic particles were observed in the samples modified by the combination of Fe and carbon. The Al-C-O-Fe-rich intermetallic particles should play a very positive role in grain refining for Mg-Al alloys. The combination of Al-C-O-Fe and Al-Fe intermetallic compounds produced more powerful nuclei for Mg grains, and thus caused grain refinement. [doi:10.2320/matertrans.MRA2007098
The effects of carbon and/or alkaline earth elements Ca and Sr on the grain refinement and tensile properties of the AZ31 alloy have been investigated in the present study. A significant grain refining efficiency could be obtained for the AZ31 alloy modified by carbon inoculation and the grain refining efficiency could be further improved by the combination of 0.2 mass%C and alkaline earth elements of 0.2 mass%Ca or 0.2 mass%Sr. Compared to the AZ31 alloy without any treatment, the tensile properties of the AZ31 alloy were remarkably improved after being modified by the combination of carbon and a little addition of alkaline earth elements. The ultimate tensile strength and elongation to failure were improved by about 20% and 40%, respectively. After being refined either by 0.2 mass%C or by the combination of 0.2 mass%C and a little addition of alkaline earth elements (0.2 mass%Ca or 0.2 mass%Sr), the main fracture mechanism was changed from cleavage mode with large cleavage planes for the unrefined AZ31 alloy to mixed mode of cleavage and quasi-cleavage fracture. The fracture surfaces were almost composed of small cleavage planes with thin river patterns and quasi-cleavage planes with small dimples and severe plastic deformation.
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