The effect of silicon content on long crack fatigue behaviour of aluminium-silicon piston alloys at elevated temperature

Microstructural characterisation using image analysis approaches combined with optical profilometry has been used to assess the fracture surfaces of test samples. The role of primary Si in enhancing crack growth rates at high ΔK levels, whilst affording improvements in crack growth rates at lower ΔK levels due to local crack deflections and shielding, has been confirmed. In the absence of primary Si (lower Si content alloys) the low ΔK level crack growth behaviour is dominated by matrix properties (intra-dendritic crack growth pre-dominates) whilst the high ΔK level crack growth behaviour is inter-dendritic and occurs along the weak path of the eutectic Si and/or intermetallic network.