MICROSTRUCTURAL INVESTIGATIONS OF MG-AL ALLOYS CONTAINING SMALL AMOUNT OF SIC NUCLEANTS

摘要

Previous investigations indicated that addition of SiC particles produces a fine microstructure in Mg-Al alloys. This work investigates the microstructure of Mg-Al alloys containing small amount of SiC particles, with an emphasis on the interactions among Mg, Al and SiC. It was found that the amount of SiC particles largely decreases after casting. It is very difficultly to detect these SiC particles under SEM and XRD due to their small sizes and amount. SEM and XRD experiments further show the existence of Mg_(17)Al_(12) and Mg_2Si phases. These Chinese script-like Mg_2Si particles are surrounded by the Mg_(17)Al_(12) particles which normally locate at the dendritic boundaries. Composition analysis shows carbon enrichment at the grain boundaries. In addition, some micro-cracks were observed close to the dendritic and grain boundaries. All these phenomena illustrate the occurrence of interactions among Mg, Al and SiC. Based on these results, the effects of these interactions on the grain refinement are discussed.