Effects of isothermal heat treatment on microstructure and properties of cast Al-7Si-4Cu alloy have been investigated.It is revealed that isothermal heat treatment

including adjusting time and temperature

can not only refine the microstructure of the alloy

but also improve the mechanical properties of the cast Al-7Si-4Cu alloy.The Si phase in microstructure of the alloy can be spheroidized and refined with extending isothermal time and increasing isothermal temperature in the condition of a given cooling rate.The disperoids in the microstructure can be observed at semi-solid temperature with holding time for 5 min

which becomes more and more with increasing in holding temperature

however

the disperoids would be disappeared with holding time for 10 min.The micro-hardness of the alloy can be improved with increasing in spheroidization and fine and uniform distribution of Si phase.