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), ob tained at a temperature of 623 K, are reported and discussed. The propertie s studied include cyclic stress response, fatigue life and nature of fractu re as a function of applied strain amplitude. The alloy exhibits moderate c yclic softening from the very first cycle till failure at all the strain am plitudes tested. The variation of high strain, low cycle fatigue life (meas ured in terms of number of reversals to failure, 2N(f)) with plastic strain amplitude (Delta epsilon(p)/2) is seen to follow a single-slope Coffin-Man son power-law relationship. The alloy is seen to fail during fatigue loadin g by a mixture of quasi-cleavage fracture and microdimples of high spatial density. Finally, a comparison of the fatigue life of the aluminium alloy i n 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 reve als that the effect of ageing on the low cycle fatigue resistance depends o n the damage parameter considered, viz. Delta epsilon(p)/2 or Delta W-p, th e average plastic strain energy per cycle. (C) 2000 Elsevier Science S.A. A ll rights reserved.