The hypereutectic Al-17Si alloys containing 2%

3%

4%

5%Fe（Wt.%） were treated by direct ultrasonic vibration（USV） treatment.The microstructures of the alloys which were produced by conventional casting process and semi-solid forming with USV treatment were investigated by OM（optical microscope）

XRD（x-ray diffraction）

and EDS（energy dispersive spectrometer）.The results reveal that a large amount of long needle-like β-Al5FeSi phase with a little plate-like δ-Al4FeSi2 phase can be observed in the as-cast Al-17Si alloy containing 2%Fe without USV treatment.With the increase of Fe content

the amount of long needle-like β-Al5FeSi phase is decreased gradually

and the plate-like δ-Al4FeSi2 phase is increased in the Al-17Si alloys.The coarse plate-like δ-Al4FeSi2 phase is dominant in Fe-rich phases in the Al-17Si alloy containing 5%Fe.The alloy melt with different Fe content was treated by USV near the liquidus temperature for a certain time

and then was poured into a permanent mold.The results indicate that blocky and short-rod δ-Al4FeSi2 phase is dominant in Fe-rich phases

and the average grain size of δ-Al4FeSi2 phase is refined to 18

4

6μm

and a little needle-like β-Al5FeSi phase is remained.The mechanism of USV refining Fe-rich phase in the Al-17Si alloys was discussed.