Abstract
The Al–9Si–0.3Fe–0.15Mn alloy was chosen as the base alloy, 0.2Mo and 0.2Zr were added in combination (0.2Mo+0.2Zr) to the base alloy to maintain the ductility and improve the strength in tensile properties. The 0.2Mo+0.2Zr addition alloy showed improvement in both ultimate tensile strength (σUTS) (160 MPa) and fracture strain (εf) (7.1%) at the as-cast conditions, compared with those (145 MPa, 6.1%) of the base alloy. The increment in the σUTS and εf by 8% and 14%, respectively, was obtained by 0.2Mo+0.2Zr addition. The eutectic α-Al with the smallest minimum nanoindentation hardness (HIT, min), showing high Al or low ΔMkeα due to heavy micro-segregation existed as a continuous phase in the 0.2Mo+0.2Zr addition alloy led to improvement in ductility. The size of the cell structure caused by the dense tangles of dislocations was about 250 nm, which corresponded to a similar size to the high Al or low ΔMkeα regions in the 0.2Mo+0.2Zr addition alloy. It was found on the basis of improvement in tensile properties that both usage of the gravity casting method and the addition of Mo and Zr, suggested the possibility for the as-cast application because the eutectic Si particles were refined, and the eutectic α-Al phase was characterized by high Al content or low ΔMkeα region caused by micro-segregation of the Mo and Zr atoms. The inhomogeneity eutectic grains including IMCs acted as the harmonic structure for the improvement in both strength and ductility.
