Micromechanisms of short fatigue crack growth in an Al-Si piston alloy

The short fatigue crack growth behaviour of a model cast aluminium piston alloy has been investigated. This has been achieved using a combination of fatigue crack replication methods at various intervals during fatigue testing and post-mortem analysis of the crack profiles. Crack-microstructure interactions have been clearly delineated using a combination of optical microscopy and scanning electron microscopy. Results show that intermetallic particles and eutectic Al-Si regions play a significant role in determining the crack path and growth rate of short fatigue cracks. It is observed that the growth of short cracks is often retarded or even arrested at intermetallic particles and Al-Si eutectic regions. Crack deflection at intermetallics and eutectic Si is also frequently observed. These results have been compared with the long crack growth behaviour of the alloy.