Fatigue crack propagation in ultrafine grained Al–Mg alloy

The fatigue crack growth rates in ultrafine grained (UFG) Al–7.5Mg were investigated and were compared to those observed in powder-metallurgy (P/M) Al–7Mg and ingot-metallurgy (I/M) Al–7Mg. Fatigue crack growth rates in UFG Al–7.5Mg are significantly higher than those of P/M Al–7Mg, which, in turn, are significantly higher than those of I/M Al–7Mg. The fatigue crack growth threshold is the lowest in the UFG Al–7.5Mg, followed by P/M Al–7Mg, and is the highest in I/M Al–7Mg. The higher fatigue crack growth rates and lower thresholds in UFG Al–7.5Mg may be attributed to the much smoother fracture surface morphology and lower roughness-induced crack closure and crack deflection.