The A390 aluminum alloy cylinder liners were prepared by gravity-casting and squeeze-casting

and their fracture behaviors under static loading were investigated by in situ SEM observation.For the gravity-casting alloy

microcracks firstly initiated at the primary Si particles however were restricted from propagating to the matrix.Meanwhile

the eutectic Si particles with a high aspect ratio played a bridging role in the dominant crack propagation

which suggested that the eutectic Si particles are more advantageous to crack propagation than primary Si particles in the gravity-casting alloy.By contrast

for the squeeze-casting alloy

microcracks also were observed to initiate firstly at the primary Si particles but then propagate to matrix and link with other microcracks to form a dominant crack.In addition

microcracks barely initiated at the spherical eutectic Si particles

and the primary Si particles were preferentially sought out by the dominant crack.The results indicate that the eutectic Si particles are in competition with primary Si particles in propagating the dominant crack.Moreover

the fracture of eutectic Si particles affect the propagation of microcracks at the primary Si particles due to the function of the eutectic Si particles to release stress.It also suggested that the primary Si particles and eutectic Si particles should be coordinated to achieve excellent mechanical properties of hypereutectic aluminum-silicon alloys.