Fracture behaviors of A390 aluminum cylinder liner alloys under static loading

A390 aluminum cylinder liner alloys were fabricated by gravity-casting and squeeze-casting, and their fracture behaviors under static loading were investigated by in situ SEM observation in this study. The two alloy samples exhibit different morphologies and sizes of eutectic and primary Si particles, which results in diverse fracture behaviors. For the gravity-casting alloy, microcracks firstly initiate at the primary Si particles but are restricted from propagating to the matrix, and the dominant crack primarily propagates through the fracturing or debonding of eutectic Si particles. By contrast, for the squeeze-casting alloy, microcracks also firstly initiate at the primary Si particles and then propagate into matrix and link with other microcracks to form a dominant crack. In addition, the microcracks are barely observed to initiate at the eutectic Si particles in squeeze-casting alloy. All results show that the eutectic Si and primary Si act as a bridging role in gravity-casting alloy and squeeze-casting alloy, respectively. It indicates that eutectic Si particles and primary Si particles are in competition in the propagation of dominant crack. Moreover, the fractures of eutectic Si particles could release elastic strain energy, by which the strain energy at crack tips is decreased, so the propagation of the microcracks at the primary Si particles could be retarded.

► Primary Si is easier to act as the microcracks initiation sites than eutectic Si or matrix.
► Eutectic Si is in competition with primary Si in propagating the dominant crack.
► The fracture of eutectic Si particles affects the propagation of microcracks.