Refinement mechanism of in-situ Al^sub 4^C^sub 3^ particles on AZ91 magnesium alloys

The effects of SrCO3 on the microstructure of AZ91 magnesium alloy were investigated by OM, SEM, EDS, XRD and DTA analyses. The results show that AZ91 magnesium alloy with 1.0% SrCO3 addition has the best refining effect at 730 ° for 20 min, the average size of the [alpha]-Mg grain in AZ91 matrix alloy is reduced from about 91 [mu]m to 58 [mu]m, with reduction of about 36%. Based on the analysis results of EDS, binding energy, and Gibbs free energy, it is evident that the grain is refined because of the generation of A1^sub 4^C^sub 3^ particles which can be used as the crystal nucleus of the magnesium alloy when SrCO3 is added. Owing to the generation of A1^sub 4^C^sub 3^ in AZ91 magnesium alloy, the grain boundary is pined and the grain growth is inhibited. In the accession to the Al^sub 4^C^sub 3^, small subcooling temperature difference leads to the formation of fine grain microstructure in alloy melt. Fine grain microstructure in AZ91 alloy melt with the addition of SrCO3 can be obtained on the condition of lower undercooling temperature according to the DTA analysis results.[PUBLICATION ABSTRACT]