THE LOW-CYCLE FATIGUE AND CYCLIC FRACTURE-BEHAVIOR OF 7150-ALUMINUM ALLOY

A study has been made to understand the low-cycle fatigue properties, the cyclic-stress response characteristics and the cyclic fracture behaviour of the high-purity aluminium alloy 7150. The alloy was cycled over a range of plastic strains giving lives of less than 10(4) cycles. The specimens were cycled using tension-compression loading under total strain control. The alloy in the ageing condition (T77) displayed softening at all plastic strain amplitudes. The presence of shearable matrix precipitates in the alloy, in the ageing condition studied, results in a local decrease in resistance to dislocation movement, leading to progressive loss of any ordering contributions to hardening. The observed softening behaviour is ascribed primarily to interactions between the dislocations and the matrix precipitates. The fracture was predominantly intergranular with tortuous crack paths. The low-cycle fatigue properties and the cyclic fracture behaviour of the alloy are discussed in terms of competing effects involving the plastic strain amplitude, response stress, intrinsic microstructural features and deformation behaviour.