Effect of forced melt flow on microstructure evolution in AlSi7Mg0.6 alloy during directional solidification

The AlSi7Mg0.6 alloy is commonly used in foundry industry to produce high stressed automotive components like motor frames and cylinder heads. The properties of the material correspond directly to their microstructure which is given by the parameters of the solidification process. The effect of forced melt flow on the microstructure evolution in AlSi7Mg0.6 alloy during directional solidification is investigated experimentally. For that purpose a Bridgman-type gradient furnace is equipped with a rotating magnetic field to induce flow in the melt. As a result the forced melt flow substantially changes the dendritic solidification microstructure. Increasing intensity of the melt flow leads to axial macrosegregation and enrichment of silicon in the centre part of a sample. Here, this yields to a transition to mixed columnar-equiaxed or even to equiaxed growth, whereas in the out-of-centre region columnar dendritic growth persists.