Influence of grain structure and slip planarity on fatigue crack growth in low alloying artificially aged 2xxx aluminium alloys

The fatigue crack growth behaviour under constant amplitude loading of three low alloying artificially aged 2xxx aluminium alloys with distinct microstructures is analysed. Fatigue crack growth tests show a correlation between fatigue performance and the occurrence of crack closure. Fractography and fracture surface measurements show that rougher surfaces give higher closure levels suggesting a dominating influence of RICC in these alloys. The relationship between the crack path and the microstructure, i.e. grain structure and slip planarity, is assessed semi-quantitatively. A criterion to evaluate the propensity for slip band formation is derived and reasonable correlation is found between the fatigue fracture behaviour of the three alloys and this criterion.