Simultaneous Primary Si Refinement and Eutectic Modification in Hypereutectic Al–Si Alloys

A solid–liquid duplex casting process was applied to achieve simultaneous refinement and modification of silicon phases in hypereutectic Al–Si alloys. In this process P-treated Al-24Si (wt%) solid alloy is mixed with Sr-treated eutectic Al-12.6Si molten alloy to provide an Al-18Si alloy in the Liquid + Primary Si phase field and then cast. By using this process the mean particle size of primary silicon was reduced from 50 μm to less than 15 μm (refinement) and the eutectic structure changed from a plate-like to a fibrous structure (modification) when compared with conventional casting process. The results of mechanical testing showed that the tensile strength increased by about 14 % from 153.5 to 175.1 MPa and the elongation more than doubled from 1.64 to 3.76 %. The improvement of mechanical properties is attributed to the combination of refined primary silicon and the fibrous structure of the modified eutectic Al–Si matrix.