Temperature Field and Microstructural Formation of Semi-Solid AlSi₇Mg Alloy

The microstructural formation of the semi-solid AlSi₇Mg alloy stirred by electromagnetic field is investigated together with the tempeatre field of the stirred melt at continuously cooling. A important kinetic factor for primary α-Al nucleation is proposed. It is found that a low temperature gradient exists in the electromagnetic stirred melt. This is why the first dendritic arms and secondary dendritic arms are refined. Experimental results also show that the root remelting of secondary dendritic arms is an important mechanism for the primary α-Al refmement. Strong electromagnetic stirring greatly reduces the composition supercooling in the melt and eliminates preferring growth of the first dendritic arms. Therefore, many rosettes or spherical Primary α-Al phase particles form finally.