Development of high strength and toughness nano-SiCp/A356 composites with ultrasonic vibration and squeeze casting

The nano-SiCp/A356 Al-matrix composites containing 2 wt.% nano-SiCp were synthesized with solid-liquid mixed casting method. The effects of ultrasonic vibration (UV) treatment and squeeze casting on refinement were studied and the role of nano-SiCp distribution on refinement was focused. Results show that both of the secondary dendritic arm spacing (SDAS) of alpha-Al grains and the size of eutectic Si phase decrease with the increase of the UV time and the applied pressure of squeeze casting. When UV is applied for 3 min, the SDAS of alpha-Al in composites is 8.1 mu m, which is reduced by 49% than that of A356 matrix alloy. The mean diameter and aspect ratio of eutectic Si phase in composites are 0.92 mu m and 2.33, and they are reduced by 42% and 32% respectively than those of A356 matrix alloy. When the applied pressure of squeeze casting is 400 MPa, SDAS of alpha-Al in composites is 6.9 mu m, which is reduced by 55% than that of A356 matrix alloy. Both the processes of UV and squeeze casting can affect the refining effects by regulating the distribution of nano-SiCp. The better the dispersion of nano-SiCp is, the better the refinement of alpha-Al and eutectic Si phase can be achieved. The mechanical properties of 2 wt.% AMNCs are improved with the increase of UV time and applied pressure, which is consistent with the refinement of the composites' microstructure.