Effect of Erbium on the Microstructure and Mechanical Properties of Semi‐Solid Al–7Si–0.4Mg Alloy

Abstract

In this paper, semi-solid Al-7Si-0.4Mg-x erbium(Er) (x ¼ 0, 0.1, 0.3, 0.5, 0.8 wt%) alloys are fabricated via electromagnetic stirring method. The effects of Er on the microstructures and mechanical properties of semi-solid Al-7Si-0.4Mg alloys are investigated. Results show that the eutectic π-phase is modified to fine sized Er-poor π-phase and primary α-Al is refined in semisolid Al-7Si-0.4Mg alloys with the addition of Er. Meanwhile, the plate-like shape eutectic Si is transformed into fibrous eutectic Si with addition of Er, which has an excellent modification effect on the eutectic Si. Nucleation rate of the Er-poor π-phase is increased with a higher super cooling rate, which causes the refinement of primary α-Al and the modification of eutectic Si phase. With the addition of 0.3 wt% Er, semi-solid Al-7Si-0.4Mg alloys obtain the best tensile properties. The ultimate tensile strength and elongation values are 228 MPa and 10.4%, which is increased by 7% and 50% than Erfree alloy, respectively.Al-7Si-0.4Mg casting alloy is widely used in the auto-motive industry because of the good specific mechanical properties. Semisolid metal processing (SSM) is widely used in Al alloys due to the spherical primary α-Al grain structure. [1][2][3] Zhang et al. [4]

Effect of erbium on the rheocast quality index of A356 semisolid feedstock

“…Another possible mechanism for grain refinement by the addition of erbium has also been reported. The Er-rich phase formed on the solid/liquid interface inhibits the growth of primary α -Al grains [39]. Grain refinement is related to a change in the solidification parameters.…”