Effect of Mechanical Vibration Frequency on Cast A357 Aluminum Alloy

The mechanical vibration was applied to the casting solidification process of A357 aluminum alloy by a constructed mechanical vibration table with a mechanical vibration frequency range of 1000-4000 Hz and an amplitude of 10μm. The differences in the microstructure and properties were analyzed by observing the metallographic microstructures,scanning electron microscope（SEM） images of the specimens prepared under the different mechanical vibration conditions.The results show that mechanical vibration can effectively improve the microstructure of A357 castings. As the increase of mechanical vibration frequency, the grain size of the solidified microstructure becomes more uniform and finer, and the eutectic silicon in the grains gradually changes from needle-like to fiber-like. The mechanical properties of A357 alloy gradually improves with the increase of mechanical vibration frequency. The fracture mode of A357 alloy under the mechanical vibration condition is a mixed type, with the appearance of both dimples and cleavage steps on the fracture surface. As the increase of mechanical vibration frequency, the number of dimples on the fracture surface gradually increases,indicating that the increase of the alloy toughness. Under four mechanical vibration frequencies of 1000 Hz, 2000 Hz, 3000 Hz and 4000 Hz, the tensile strength of A357 alloy is 275.4 MPa, 281.3 MPa, 292.7 MPa and 311.3 MPa, the yield strength is 235.6 MPa, 241.1 MPa, 249.7 MPa and 264.6 MPa, and the elongation is 2.57%, 2.73%, 3.37% and 4.10%, respectively.