Effects of isothermal treatment process and injection speed on microstructure and mechanical properties of thixo-forming Al-30Si alloy with 1% P modification were investigated by SEM（scanning electron microscope）

XRD（X-ray diffraction） and tensile testing.The results show that the morphology of primary Si phase exhibits more spherical with disappearance of acicular eutectic Si phase compared with as-cast microstructure

while α-Al phase is dispersedly distributed in the matrix as a result of broking into.A part of α-Al phase is retained in the slurry with the higher solid fraction.Ambient tensile strength of the alloy with holding at 620℃ for 100 min and 120 min firstly increases and then decreases with increasing in injection velocity

while for the 100 min

the maximum value of tensile strength is 226MPa at 6 m/s

and for 120 min

it is 230 MPa at 4 m/s.However

with holding at 630℃ for 120 min

tensile strength of the alloy is gradually decreased with the increase of the injection velocity.