Structure-property correlation of eutectic Al-12.4 Si alloys with and without Zirconium (Zr) addition

The effect of Zr (0.1, 0.3, 0.5 wt. %) addition on microstructural morphology, hardness, mechanical properties and fracture behaviour of gravity cast Al-12.4Si alloy has been studied. The unmodified Al-12.4Si alloy consists of non-uniformly distributed coarse and irregular shape primary and eutectic silicon particles with sharp corners in Al phase. However, the Zr added Al-12.4Si alloys have uniformly distributed fine eutectic and primary Si particles with blunt corners due to formation of Al3Zr, which acts as heterogeneous nucleation site for Si. The bulk hardness of the modified alloy is slightly increased, but ultimate tensile strength (UTS), yield strength (YS) and elongation (%El) are increased significantly as an effect of microstructural morphology modification. Further, fractographs reveal that the brittle mode of fracture and cleavage fracture of Si particles decreased and ductile fracture with dimples formation increased in the modified alloy.