The influence of different temperatures and time on the precipitation and coarsening behavior of secondary Al3Sc in the Al-Sc alloy and the role of the secondary Al3Sc in properties of Al-Sc alloy were investigated.It is concluded that the coarsening behavior follows the kinetic law of the Lifshitz-Slyozov-Wagner（LSW） theory with the alloys aged at 350 ℃

400 ℃ or 450 ℃

and it is predicted approximately by the LSW theory at 500 ℃ within 1 hour

however

departed from the LSW theory with a lower coarsening speed at 500 ℃ with aged more than 1 hour.The hardness of Al-Sc alloys is decreased with the particles radius increasing in the range of 4

4

0 nm.When the radius of Al3Sc is in range of 4

7

.5 nm

the alloy hardness reaches its peak value of about 750

8

50 MPa

nearly 3.75

4

.25 times of the value before heat treatment

exhibiting significantly precipitating strengthening effects.When the particle radius reaches 40 nm

the alloy hardness reduces to 300 MPa.