Super long life fatigue properties of Al-Si eutectic alloy by rotating-bending and tension-compression fatigue tests

摘要

To investigate the effect of the Si-phase on fatigue properties of Al-Si eutectic alloys in a long life fatigue range (N≤10{sup}7) and super long life fatigue range (N>10{sup}8), rotating-bending and tension-compression fatigue tests and FEManalysis were carried out. Fatigue test specimens were prepared from two materials produced by two processes: continuous casting and extrusion. The results obtained are as follows. (1) In the case of continuous casting, all fatigue fractures were causedby shear-type cracks, resulting in shorter fatigue life. (2) In the case of extrusion, the fatigue fracture origin in the long life fatigue range was in the Si-phase, while in the super long fatigue range it was in the matrix. (3) The fatigue limitdefined by the cycle N = 10{sup}7 can be predicted using the square root of (area) parameter model, i.e. with two parameters, the maximum size of Si-phase square root of (area){sub}(max) and the Vickers hardness Hv of Al-marix, without the influence ofthe Si-phase. (4) In the case of Al-Si alloy, a crack leading to fracture initiates even after 10{sup}8 cycles under very low stress. Thus, super long life fatigue behavior must be taken into account to both material and structural designs.