Microstructure and mechanical properties of rheo-diecast hypereutectic Al–Si alloy with 2%Fe assisted with ultrasonic vibration process

• The δ-Al4(Fe,Mn)Si2 phase is refined in the alloy produced by rheo-diecasting (RDC).
• The mechanical properties of the RDC samples are increased obviously.
• The optimum temperature range of USV treatment is 665–645 °C.
• The α phase keeps invariant in both morphology and composition after T6 treatment.

The microstructure and mechanical properties of Al–17Si–2Fe–2Cu–1Ni–0.8Mn alloy produced by rheo-diecasting (RDC) were studied. The semisolid slurry used in the RDC process was prepared by ultrasonic vibration (USV). The results show that the microstructure of the alloy produced by conventional die casting (DC) contains a large amount of coarse plate-like δ-Al4(Fe, Mn)Si2 phase with average length of about 100 μm and polygonal α-Al15(Fe, Mn)3Si2 phase. The δ-Al4(Fe, Mn)Si2 phase is refined into fine block-like particles with average grain size of about 17 μm in the alloy produced by RDC assisted with USV treatment in the temperature range of 665–645 °C. In T6 condition, the ultimate tensile strength (UTS), elongation and hardness of the RDC tensile sample at room temperature are 309 MPa, 0.8% and 141HB, respectively. Compared with the DC sample, the UTS, elongation and hardness of the RDC sample at room temperature are increased by 34.9%, 40.4% and 17.5%, respectively. The UTS at 350 °C of the RDC sample is also increased obviously and reaches 135 MPa. It is considered that USV can effectively refine the δ-Al4(Fe, Mn)Si2 phase. The refinement of δ-Al4(Fe, Mn)Si2 phase and elimination of the porosities are the main reasons for the increase of the mechanical properties of the RDC sample.