High temperature, low cycle fatigue behaviour of an aluminium alloy (Al–12Si–CuMgNi)

The low cycle fatigue properties of an aluminium alloy (Al–12Si–CuMgNi), obtained at a temperature of 623 K, are reported and discussed. The properties studied include cyclic stress response, fatigue life and nature of fracture as a function of applied strain amplitude. The alloy exhibits moderate cyclic softening from the very first cycle till failure at all the strain amplitudes tested. The variation of high strain, low cycle fatigue life (measured in terms of number of reversals to failure, 2Nf) with plastic strain amplitude (Δεp/2) is seen to follow a single-slope Coffin–Manson power-law relationship. The alloy is seen to fail during fatigue loading by a mixture of quasi-cleavage fracture and microdimples of high spatial density. Finally, a comparison of the fatigue life of the aluminium alloy in the over-aged (OA) condition (obtained from the present study) with that of the alloy in a highly over-aged (HOA) condition of an earlier study reveals that the effect of ageing on the low cycle fatigue resistance depends on the damage parameter considered, viz. Δεp/2 or ΔWp, the average plastic strain energy per cycle.