Microstructural effects on short fatigue crack propagation in cast Al-Si alloys

The role of microstructure on the short fatigue crack behaviour of cast Al-Si alloy under high cycle loading conditions is investigated by tracking the progress of cracks through fine, medium and coarse microstructured samples. Generally, in the early stage of crack growth, short cracks mainly grow transgranularly, with cracks growth close to low index crystallographic planes (mainly {1 0 0}) in some grains and frequently inhibited at grain boundaries. In the late stage, the crack growth mode gradually shifts from crystallographic stage-I to non-crystallographic stage-II. The short cracks grow faster and fluctuate significantly according to local microstructure. Our results show that finer microstructures offer greater crack nucleation and propagation resistance.