Modification of the Structural, Microstructural, and Elastoplastic Properties of Aluminum Wires after Operation

The health of the components that make up the cables of power lines, and hence their service life, is governed at the micro level by changes in their structure and microstructure. In this paper, the structure and microstructure of aluminum wires of overhead power transmission lines (without a steel core) of different service life from 0 to 62 years have been investigated by quantitative techniques of X-ray diffraction, diffraction of back-scattered electrons, and the densitometric method. Elastoplastic properties of the wires have been tested by the acoustic-resonance method. A decrease in the Al material density & UDelta;rho/rho & SIM;-0.165% was found in the near-surface layer of & SIM;36 mu m depth and in the bulk of the wires with an increase in the service life from 0 to 18 years. The density decrease is associated with the accumulation of microcracks. The following density increase (& UDelta;rho/rho & SIM;-0.06%) in wires with a service life of 62 years is attributed to the formation of & SIM;0.7 vol.% of crystalline Al oxides in the near-surface layers of the wires. The nature of the change in the elastic modulus, microplastic flow stress, and decrement indicates complex structural changes correlating with the results obtained by diffraction methods.